[patch 0/9] mount ownership and unprivileged mount syscall (v6)

[patch 0/9] mount ownership and unprivileged mount syscall (v6)

[Miklos Szeredi]

After much sitting in -mm, Andrew dropped this patchset due to
conflicts with other stuff.  It would be nice, if it could be reviewed
in time for 2.6.26 (2.6.25 is closed as far as I understand).

v5 -> v6:

 - update to latest -mm
 - preliminary util-linux-ng support (will post right after this series)

Thanks,
Miklos

--

[patch 1/9] unprivileged mounts: add user mounts to the kernel

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-add-user-mounts-to-the-kernel.patch --]
[-- Type: text/plain, Size: 8559 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

This patchset adds support for keeping mount ownership information in the
kernel, and allow unprivileged mount(2) and umount(2) in certain cases.

The mount owner has the following privileges:

  - unmount the owned mount
  - create a submount under the owned mount

The sysadmin can set the owner explicitly on mount and remount.  When an
unprivileged user creates a mount, then the owner is automatically set to the
user.

The following use cases are envisioned:

1) Private namespace, with selected mounts owned by user.  E.g.
   /home/$USER is a good candidate for allowing unpriv mounts and unmounts
   within.

2) Private namespace, with all mounts owned by user and having the "nosuid"
   flag.  User can mount and umount anywhere within the namespace, but suid
   programs will not work.

3) Global namespace, with a designated directory, which is a mount owned by
   the user.  E.g.  /mnt/users/$USER is set up so that it is bind mounted onto
   itself, and set to be owned by $USER.  The user can add/remove mounts only
   under this directory.

The following extra security measures are taken for unprivileged mounts:

 - usermounts are limited by a sysctl tunable
 - force "nosuid,nodev" mount options on the created mount

For testing unprivileged mounts (and for other purposes) simple
mount/umount utilities are available from:

  http://www.kernel.org/pub/linux/kernel/people/mszeredi/mmount/

After this series I'll be posting a preliminary patch for util-linux-ng,
to add the same functionality to mount(8) and umount(8).

This patch:

A new mount flag, MS_SETUSER is used to make a mount owned by a user.  If this
flag is specified, then the owner will be set to the current fsuid and the
mount will be marked with the MNT_USER flag.  On remount don't preserve
previous owner, and treat MS_SETUSER as for a new mount.  The MS_SETUSER flag
is ignored on mount move.

The MNT_USER flag is not copied on any kind of mount cloning: namespace
creation, binding or propagation.  For bind mounts the cloned mount(s) are set
to MNT_USER depending on the MS_SETUSER mount flag.  In all the other cases
MNT_USER is always cleared.

For MNT_USER mounts a "user=UID" option is added to /proc/PID/mounts.  This is
compatible with how mount ownership is stored in /etc/mtab.

The rationale for using MS_SETUSER and MNT_USER, to distinguish "user"
mounts from "non-user" or "legacy" mounts are follows:

  a) Mount(2) and umount(2) on legacy mounts always need CAP_SYS_ADMIN
     capability.  As opposed to user mounts, which will only require,
     that the mount owner matches the current fsuid.  So a process
     with fsuid=0 should not be able to mount/umount legacy mounts
     without the CAP_SYS_ADMIN capability.

  b) Legacy userspace programs may set fsuid to nonzero before calling
     mount(2).  In such an unlikely case, this patchset would cause
     an unintended side effect of making the mount owned by the fsuid.

  c) For legacy mounts, no "user=UID" option should be shown in
     /proc/mounts for backwards compatibility.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-03 22:10:10.000000000 +0100
+++ linux/fs/namespace.c	2008-01-04 13:46:33.000000000 +0100
@@ -477,6 +477,13 @@ static struct vfsmount *skip_mnt_tree(st
 	return p;
 }
 
+static void set_mnt_user(struct vfsmount *mnt)
+{
+	BUG_ON(mnt->mnt_flags & MNT_USER);
+	mnt->mnt_uid = current->fsuid;
+	mnt->mnt_flags |= MNT_USER;
+}
+
 static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
 					int flag)
 {
@@ -491,6 +498,11 @@ static struct vfsmount *clone_mnt(struct
 		mnt->mnt_mountpoint = mnt->mnt_root;
 		mnt->mnt_parent = mnt;
 
+		/* don't copy the MNT_USER flag */
+		mnt->mnt_flags &= ~MNT_USER;
+		if (flag & CL_SETUSER)
+			set_mnt_user(mnt);
+
 		if (flag & CL_SLAVE) {
 			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
 			mnt->mnt_master = old;
@@ -644,6 +656,8 @@ static int show_vfsmnt(struct seq_file *
 		if (mnt->mnt_flags & fs_infop->flag)
 			seq_puts(m, fs_infop->str);
 	}
+	if (mnt->mnt_flags & MNT_USER)
+		seq_printf(m, ",user=%i", mnt->mnt_uid);
 	if (mnt->mnt_sb->s_op->show_options)
 		err = mnt->mnt_sb->s_op->show_options(m, mnt);
 	seq_puts(m, " 0 0\n");
@@ -1181,8 +1195,9 @@ static int do_change_type(struct nameida
 /*
  * do loopback mount.
  */
-static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
+static int do_loopback(struct nameidata *nd, char *old_name, int flags)
 {
+	int clone_fl;
 	struct nameidata old_nd;
 	struct vfsmount *mnt = NULL;
 	int err = mount_is_safe(nd);
@@ -1202,11 +1217,12 @@ static int do_loopback(struct nameidata 
 	if (!check_mnt(nd->path.mnt) || !check_mnt(old_nd.path.mnt))
 		goto out;
 
+	clone_fl = (flags & MS_SETUSER) ? CL_SETUSER : 0;
 	err = -ENOMEM;
-	if (recurse)
-		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, 0);
+	if (flags & MS_REC)
+		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
 	else
-		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, 0);
+		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
 
 	if (!mnt)
 		goto out;
@@ -1268,8 +1284,11 @@ static int do_remount(struct nameidata *
 		err = change_mount_flags(nd->path.mnt, flags);
 	else
 		err = do_remount_sb(sb, flags, data, 0);
-	if (!err)
+	if (!err) {
 		nd->path.mnt->mnt_flags = mnt_flags;
+		if (flags & MS_SETUSER)
+			set_mnt_user(nd->path.mnt);
+	}
 	up_write(&sb->s_umount);
 	if (!err)
 		security_sb_post_remount(nd->path.mnt, flags, data);
@@ -1378,10 +1397,13 @@ static int do_new_mount(struct nameidata
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	mnt = do_kern_mount(type, flags, name, data);
+	mnt = do_kern_mount(type, flags & ~MS_SETUSER, name, data);
 	if (IS_ERR(mnt))
 		return PTR_ERR(mnt);
 
+	if (flags & MS_SETUSER)
+		set_mnt_user(mnt);
+
 	return do_add_mount(mnt, nd, mnt_flags, NULL);
 }
 
@@ -1413,7 +1435,8 @@ int do_add_mount(struct vfsmount *newmnt
 	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
 		goto unlock;
 
-	newmnt->mnt_flags = mnt_flags;
+	/* MNT_USER was set earlier */
+	newmnt->mnt_flags |= mnt_flags;
 	if ((err = graft_tree(newmnt, nd)))
 		goto unlock;
 
@@ -1735,7 +1758,7 @@ long do_mount(char *dev_name, char *dir_
 		retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
 				    data_page);
 	else if (flags & MS_BIND)
-		retval = do_loopback(&nd, dev_name, flags & MS_REC);
+		retval = do_loopback(&nd, dev_name, flags);
 	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
 		retval = do_change_type(&nd, flags);
 	else if (flags & MS_MOVE)
Index: linux/fs/pnode.h
===================================================================
--- linux.orig/fs/pnode.h	2008-01-03 22:10:10.000000000 +0100
+++ linux/fs/pnode.h	2008-01-04 13:45:45.000000000 +0100
@@ -23,6 +23,7 @@
 #define CL_MAKE_SHARED 		0x08
 #define CL_PROPAGATION 		0x10
 #define CL_PRIVATE 		0x20
+#define CL_SETUSER		0x40
 
 static inline void set_mnt_shared(struct vfsmount *mnt)
 {
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h	2008-01-03 22:10:10.000000000 +0100
+++ linux/include/linux/fs.h	2008-01-04 13:45:46.000000000 +0100
@@ -125,6 +125,7 @@ extern int dir_notify_enable;
 #define MS_RELATIME	(1<<21)	/* Update atime relative to mtime/ctime. */
 #define MS_KERNMOUNT	(1<<22) /* this is a kern_mount call */
 #define MS_I_VERSION	(1<<23) /* Update inode I_version field */
+#define MS_SETUSER	(1<<24) /* set mnt_uid to current user */
 #define MS_ACTIVE	(1<<30)
 #define MS_NOUSER	(1<<31)
 
Index: linux/include/linux/mount.h
===================================================================
--- linux.orig/include/linux/mount.h	2008-01-03 22:10:10.000000000 +0100
+++ linux/include/linux/mount.h	2008-01-04 13:45:45.000000000 +0100
@@ -33,6 +33,7 @@ struct mnt_namespace;
 
 #define MNT_SHRINKABLE	0x100
 #define MNT_IMBALANCED_WRITE_COUNT	0x200 /* just for debugging */
+#define MNT_USER	0x400
 
 #define MNT_SHARED	0x1000	/* if the vfsmount is a shared mount */
 #define MNT_UNBINDABLE	0x2000	/* if the vfsmount is a unbindable mount */
@@ -69,6 +70,8 @@ struct vfsmount {
 	 * are held, and all mnt_writer[]s on this mount have 0 as their ->count
 	 */
 	atomic_t __mnt_writers;
+
+	uid_t mnt_uid;			/* owner of the mount */
 };
 
 static inline struct vfsmount *mntget(struct vfsmount *mnt)

--

Re: [patch 1/9] unprivileged mounts: add user mounts to the kernel

[Pavel Machek]

On Tue 2008-01-08 12:35:03, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> This patchset adds support for keeping mount ownership information in the
> kernel, and allow unprivileged mount(2) and umount(2) in certain cases.
> 
> The mount owner has the following privileges:
> 
>   - unmount the owned mount
>   - create a submount under the owned mount

- create unkillable processes
- block suspend/hibernation

?
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [patch 1/9] unprivileged mounts: add user mounts to the kernel

[Pavel Machek]

On Tue 2008-01-08 12:35:03, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> This patchset adds support for keeping mount ownership information in the
> kernel, and allow unprivileged mount(2) and umount(2) in certain cases.
> 
> The mount owner has the following privileges:
> 
>   - unmount the owned mount
>   - create a submount under the owned mount

- create traps for updatedb, etc?

Is there Doc* file somewhere describing dangers of allowing this?
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [patch 1/9] unprivileged mounts: add user mounts to the kernel

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> This patchset adds support for keeping mount ownership information in the
> kernel, and allow unprivileged mount(2) and umount(2) in certain cases.
> 
> The mount owner has the following privileges:
> 
>   - unmount the owned mount
>   - create a submount under the owned mount
> 
> The sysadmin can set the owner explicitly on mount and remount.  When an
> unprivileged user creates a mount, then the owner is automatically set to the
> user.
> 
> The following use cases are envisioned:
> 
> 1) Private namespace, with selected mounts owned by user.  E.g.
>    /home/$USER is a good candidate for allowing unpriv mounts and unmounts
>    within.
> 
> 2) Private namespace, with all mounts owned by user and having the "nosuid"
>    flag.  User can mount and umount anywhere within the namespace, but suid
>    programs will not work.
> 
> 3) Global namespace, with a designated directory, which is a mount owned by
>    the user.  E.g.  /mnt/users/$USER is set up so that it is bind mounted onto
>    itself, and set to be owned by $USER.  The user can add/remove mounts only
>    under this directory.
> 
> The following extra security measures are taken for unprivileged mounts:
> 
>  - usermounts are limited by a sysctl tunable
>  - force "nosuid,nodev" mount options on the created mount
> 
> For testing unprivileged mounts (and for other purposes) simple
> mount/umount utilities are available from:
> 
>   http://www.kernel.org/pub/linux/kernel/people/mszeredi/mmount/
> 
> After this series I'll be posting a preliminary patch for util-linux-ng,
> to add the same functionality to mount(8) and umount(8).
> 
> This patch:
> 
> A new mount flag, MS_SETUSER is used to make a mount owned by a user.  If this
> flag is specified, then the owner will be set to the current fsuid and the
> mount will be marked with the MNT_USER flag.  On remount don't preserve
> previous owner, and treat MS_SETUSER as for a new mount.  The MS_SETUSER flag
> is ignored on mount move.
> 
> The MNT_USER flag is not copied on any kind of mount cloning: namespace
> creation, binding or propagation.  For bind mounts the cloned mount(s) are set
> to MNT_USER depending on the MS_SETUSER mount flag.  In all the other cases
> MNT_USER is always cleared.
> 
> For MNT_USER mounts a "user=UID" option is added to /proc/PID/mounts.  This is
> compatible with how mount ownership is stored in /etc/mtab.
> 
> The rationale for using MS_SETUSER and MNT_USER, to distinguish "user"
> mounts from "non-user" or "legacy" mounts are follows:
> 
>   a) Mount(2) and umount(2) on legacy mounts always need CAP_SYS_ADMIN
>      capability.  As opposed to user mounts, which will only require,
>      that the mount owner matches the current fsuid.  So a process
>      with fsuid=0 should not be able to mount/umount legacy mounts
>      without the CAP_SYS_ADMIN capability.
> 
>   b) Legacy userspace programs may set fsuid to nonzero before calling
>      mount(2).  In such an unlikely case, this patchset would cause
>      an unintended side effect of making the mount owned by the fsuid.
> 
>   c) For legacy mounts, no "user=UID" option should be shown in
>      /proc/mounts for backwards compatibility.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

This looks good to me.

Acked-by: Serge Hallyn <serue@us.ibm.com>

thanks,
-serge

> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-03 22:10:10.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-04 13:46:33.000000000 +0100
> @@ -477,6 +477,13 @@ static struct vfsmount *skip_mnt_tree(st
>  	return p;
>  }
> 
> +static void set_mnt_user(struct vfsmount *mnt)
> +{
> +	BUG_ON(mnt->mnt_flags & MNT_USER);
> +	mnt->mnt_uid = current->fsuid;
> +	mnt->mnt_flags |= MNT_USER;
> +}
> +
>  static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
>  					int flag)
>  {
> @@ -491,6 +498,11 @@ static struct vfsmount *clone_mnt(struct
>  		mnt->mnt_mountpoint = mnt->mnt_root;
>  		mnt->mnt_parent = mnt;
> 
> +		/* don't copy the MNT_USER flag */
> +		mnt->mnt_flags &= ~MNT_USER;
> +		if (flag & CL_SETUSER)
> +			set_mnt_user(mnt);
> +
>  		if (flag & CL_SLAVE) {
>  			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
>  			mnt->mnt_master = old;
> @@ -644,6 +656,8 @@ static int show_vfsmnt(struct seq_file *
>  		if (mnt->mnt_flags & fs_infop->flag)
>  			seq_puts(m, fs_infop->str);
>  	}
> +	if (mnt->mnt_flags & MNT_USER)
> +		seq_printf(m, ",user=%i", mnt->mnt_uid);
>  	if (mnt->mnt_sb->s_op->show_options)
>  		err = mnt->mnt_sb->s_op->show_options(m, mnt);
>  	seq_puts(m, " 0 0\n");
> @@ -1181,8 +1195,9 @@ static int do_change_type(struct nameida
>  /*
>   * do loopback mount.
>   */
> -static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
> +static int do_loopback(struct nameidata *nd, char *old_name, int flags)
>  {
> +	int clone_fl;
>  	struct nameidata old_nd;
>  	struct vfsmount *mnt = NULL;
>  	int err = mount_is_safe(nd);
> @@ -1202,11 +1217,12 @@ static int do_loopback(struct nameidata 
>  	if (!check_mnt(nd->path.mnt) || !check_mnt(old_nd.path.mnt))
>  		goto out;
> 
> +	clone_fl = (flags & MS_SETUSER) ? CL_SETUSER : 0;
>  	err = -ENOMEM;
> -	if (recurse)
> -		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, 0);
> +	if (flags & MS_REC)
> +		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
>  	else
> -		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, 0);
> +		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
> 
>  	if (!mnt)
>  		goto out;
> @@ -1268,8 +1284,11 @@ static int do_remount(struct nameidata *
>  		err = change_mount_flags(nd->path.mnt, flags);
>  	else
>  		err = do_remount_sb(sb, flags, data, 0);
> -	if (!err)
> +	if (!err) {
>  		nd->path.mnt->mnt_flags = mnt_flags;
> +		if (flags & MS_SETUSER)
> +			set_mnt_user(nd->path.mnt);
> +	}
>  	up_write(&sb->s_umount);
>  	if (!err)
>  		security_sb_post_remount(nd->path.mnt, flags, data);
> @@ -1378,10 +1397,13 @@ static int do_new_mount(struct nameidata
>  	if (!capable(CAP_SYS_ADMIN))
>  		return -EPERM;
> 
> -	mnt = do_kern_mount(type, flags, name, data);
> +	mnt = do_kern_mount(type, flags & ~MS_SETUSER, name, data);
>  	if (IS_ERR(mnt))
>  		return PTR_ERR(mnt);
> 
> +	if (flags & MS_SETUSER)
> +		set_mnt_user(mnt);
> +
>  	return do_add_mount(mnt, nd, mnt_flags, NULL);
>  }
> 
> @@ -1413,7 +1435,8 @@ int do_add_mount(struct vfsmount *newmnt
>  	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
>  		goto unlock;
> 
> -	newmnt->mnt_flags = mnt_flags;
> +	/* MNT_USER was set earlier */
> +	newmnt->mnt_flags |= mnt_flags;
>  	if ((err = graft_tree(newmnt, nd)))
>  		goto unlock;
> 
> @@ -1735,7 +1758,7 @@ long do_mount(char *dev_name, char *dir_
>  		retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
>  				    data_page);
>  	else if (flags & MS_BIND)
> -		retval = do_loopback(&nd, dev_name, flags & MS_REC);
> +		retval = do_loopback(&nd, dev_name, flags);
>  	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
>  		retval = do_change_type(&nd, flags);
>  	else if (flags & MS_MOVE)
> Index: linux/fs/pnode.h
> ===================================================================
> --- linux.orig/fs/pnode.h	2008-01-03 22:10:10.000000000 +0100
> +++ linux/fs/pnode.h	2008-01-04 13:45:45.000000000 +0100
> @@ -23,6 +23,7 @@
>  #define CL_MAKE_SHARED 		0x08
>  #define CL_PROPAGATION 		0x10
>  #define CL_PRIVATE 		0x20
> +#define CL_SETUSER		0x40
> 
>  static inline void set_mnt_shared(struct vfsmount *mnt)
>  {
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h	2008-01-03 22:10:10.000000000 +0100
> +++ linux/include/linux/fs.h	2008-01-04 13:45:46.000000000 +0100
> @@ -125,6 +125,7 @@ extern int dir_notify_enable;
>  #define MS_RELATIME	(1<<21)	/* Update atime relative to mtime/ctime. */
>  #define MS_KERNMOUNT	(1<<22) /* this is a kern_mount call */
>  #define MS_I_VERSION	(1<<23) /* Update inode I_version field */
> +#define MS_SETUSER	(1<<24) /* set mnt_uid to current user */
>  #define MS_ACTIVE	(1<<30)
>  #define MS_NOUSER	(1<<31)
> 
> Index: linux/include/linux/mount.h
> ===================================================================
> --- linux.orig/include/linux/mount.h	2008-01-03 22:10:10.000000000 +0100
> +++ linux/include/linux/mount.h	2008-01-04 13:45:45.000000000 +0100
> @@ -33,6 +33,7 @@ struct mnt_namespace;
> 
>  #define MNT_SHRINKABLE	0x100
>  #define MNT_IMBALANCED_WRITE_COUNT	0x200 /* just for debugging */
> +#define MNT_USER	0x400
> 
>  #define MNT_SHARED	0x1000	/* if the vfsmount is a shared mount */
>  #define MNT_UNBINDABLE	0x2000	/* if the vfsmount is a unbindable mount */
> @@ -69,6 +70,8 @@ struct vfsmount {
>  	 * are held, and all mnt_writer[]s on this mount have 0 as their ->count
>  	 */
>  	atomic_t __mnt_writers;
> +
> +	uid_t mnt_uid;			/* owner of the mount */
>  };
> 
>  static inline struct vfsmount *mntget(struct vfsmount *mnt)
> 
> --

[patch 2/9] unprivileged mounts: allow unprivileged umount

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-allow-unprivileged-umount.patch --]
[-- Type: text/plain, Size: 1477 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

The owner doesn't need sysadmin capabilities to call umount().

Similar behavior as umount(8) on mounts having "user=UID" option in /etc/mtab.
The difference is that umount also checks /etc/fstab, presumably to exclude
another mount on the same mountpoint.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-03 20:52:38.000000000 +0100
+++ linux/fs/namespace.c	2008-01-03 21:14:16.000000000 +0100
@@ -894,6 +894,27 @@ static int do_umount(struct vfsmount *mn
 	return retval;
 }
 
+static bool is_mount_owner(struct vfsmount *mnt, uid_t uid)
+{
+	return (mnt->mnt_flags & MNT_USER) && mnt->mnt_uid == uid;
+}
+
+/*
+ * umount is permitted for
+ *  - sysadmin
+ *  - mount owner, if not forced umount
+ */
+static bool permit_umount(struct vfsmount *mnt, int flags)
+{
+	if (capable(CAP_SYS_ADMIN))
+		return true;
+
+	if (flags & MNT_FORCE)
+		return false;
+
+	return is_mount_owner(mnt, current->fsuid);
+}
+
 /*
  * Now umount can handle mount points as well as block devices.
  * This is important for filesystems which use unnamed block devices.
@@ -917,7 +938,7 @@ asmlinkage long sys_umount(char __user *
 		goto dput_and_out;
 
 	retval = -EPERM;
-	if (!capable(CAP_SYS_ADMIN))
+	if (!permit_umount(nd.path.mnt, flags))
 		goto dput_and_out;
 
 	retval = do_umount(nd.path.mnt, flags);

--

Re: [patch 2/9] unprivileged mounts: allow unprivileged umount

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> The owner doesn't need sysadmin capabilities to call umount().
> 
> Similar behavior as umount(8) on mounts having "user=UID" option in /etc/mtab.
> The difference is that umount also checks /etc/fstab, presumably to exclude
> another mount on the same mountpoint.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Acked-by: Serge Hallyn <serue@us.ibm.com>

> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-03 20:52:38.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-03 21:14:16.000000000 +0100
> @@ -894,6 +894,27 @@ static int do_umount(struct vfsmount *mn
>  	return retval;
>  }
> 
> +static bool is_mount_owner(struct vfsmount *mnt, uid_t uid)
> +{
> +	return (mnt->mnt_flags & MNT_USER) && mnt->mnt_uid == uid;
> +}
> +
> +/*
> + * umount is permitted for
> + *  - sysadmin
> + *  - mount owner, if not forced umount
> + */
> +static bool permit_umount(struct vfsmount *mnt, int flags)
> +{
> +	if (capable(CAP_SYS_ADMIN))
> +		return true;
> +
> +	if (flags & MNT_FORCE)
> +		return false;
> +
> +	return is_mount_owner(mnt, current->fsuid);
> +}
> +
>  /*
>   * Now umount can handle mount points as well as block devices.
>   * This is important for filesystems which use unnamed block devices.
> @@ -917,7 +938,7 @@ asmlinkage long sys_umount(char __user *
>  		goto dput_and_out;
> 
>  	retval = -EPERM;
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!permit_umount(nd.path.mnt, flags))
>  		goto dput_and_out;
> 
>  	retval = do_umount(nd.path.mnt, flags);
> 
> --

[patch 3/9] unprivileged mounts: account user mounts

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-account-user-mounts.patch --]
[-- Type: text/plain, Size: 4213 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Add sysctl variables for accounting and limiting the number of user
mounts.

The maximum number of user mounts is set to 1024 by default.  This
won't in itself enable user mounts, setting a mount to be owned by a
user is first needed

[akpm]
 - don't use enumerated sysctls

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/Documentation/filesystems/proc.txt
===================================================================
--- linux.orig/Documentation/filesystems/proc.txt	2008-01-03 17:12:58.000000000 +0100
+++ linux/Documentation/filesystems/proc.txt	2008-01-03 21:15:35.000000000 +0100
@@ -1012,6 +1012,15 @@ reaches aio-max-nr then io_setup will fa
 raising aio-max-nr does not result in the pre-allocation or re-sizing
 of any kernel data structures.
 
+nr_user_mounts and max_user_mounts
+----------------------------------
+
+These represent the number of "user" mounts and the maximum number of
+"user" mounts respectively.  User mounts may be created by
+unprivileged users.  User mounts may also be created with sysadmin
+privileges on behalf of a user, in which case nr_user_mounts may
+exceed max_user_mounts.
+
 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
 -----------------------------------------------------------
 
Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-03 21:14:16.000000000 +0100
+++ linux/fs/namespace.c	2008-01-03 21:15:35.000000000 +0100
@@ -44,6 +44,9 @@ static struct list_head *mount_hashtable
 static struct kmem_cache *mnt_cache __read_mostly;
 static struct rw_semaphore namespace_sem;
 
+int nr_user_mounts;
+int max_user_mounts = 1024;
+
 /* /sys/fs */
 struct kobject *fs_kobj;
 EXPORT_SYMBOL_GPL(fs_kobj);
@@ -477,11 +480,30 @@ static struct vfsmount *skip_mnt_tree(st
 	return p;
 }
 
+static void dec_nr_user_mounts(void)
+{
+	spin_lock(&vfsmount_lock);
+	nr_user_mounts--;
+	spin_unlock(&vfsmount_lock);
+}
+
 static void set_mnt_user(struct vfsmount *mnt)
 {
 	BUG_ON(mnt->mnt_flags & MNT_USER);
 	mnt->mnt_uid = current->fsuid;
 	mnt->mnt_flags |= MNT_USER;
+	spin_lock(&vfsmount_lock);
+	nr_user_mounts++;
+	spin_unlock(&vfsmount_lock);
+}
+
+static void clear_mnt_user(struct vfsmount *mnt)
+{
+	if (mnt->mnt_flags & MNT_USER) {
+		mnt->mnt_uid = 0;
+		mnt->mnt_flags &= ~MNT_USER;
+		dec_nr_user_mounts();
+	}
 }
 
 static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
@@ -542,6 +564,7 @@ static inline void __mntput(struct vfsmo
 	 */
 	WARN_ON(atomic_read(&mnt->__mnt_writers));
 	dput(mnt->mnt_root);
+	clear_mnt_user(mnt);
 	free_vfsmnt(mnt);
 	deactivate_super(sb);
 }
@@ -1306,6 +1329,7 @@ static int do_remount(struct nameidata *
 	else
 		err = do_remount_sb(sb, flags, data, 0);
 	if (!err) {
+		clear_mnt_user(nd->path.mnt);
 		nd->path.mnt->mnt_flags = mnt_flags;
 		if (flags & MS_SETUSER)
 			set_mnt_user(nd->path.mnt);
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h	2008-01-03 20:52:38.000000000 +0100
+++ linux/include/linux/fs.h	2008-01-03 21:15:35.000000000 +0100
@@ -50,6 +50,9 @@ extern struct inodes_stat_t inodes_stat;
 
 extern int leases_enable, lease_break_time;
 
+extern int nr_user_mounts;
+extern int max_user_mounts;
+
 #ifdef CONFIG_DNOTIFY
 extern int dir_notify_enable;
 #endif
Index: linux/kernel/sysctl.c
===================================================================
--- linux.orig/kernel/sysctl.c	2008-01-03 17:13:22.000000000 +0100
+++ linux/kernel/sysctl.c	2008-01-03 21:15:35.000000000 +0100
@@ -1288,6 +1288,22 @@ static struct ctl_table fs_table[] = {
 #endif	
 #endif
 	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "nr_user_mounts",
+		.data		= &nr_user_mounts,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= &proc_dointvec,
+	},
+	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "max_user_mounts",
+		.data		= &max_user_mounts,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
+	{
 		.ctl_name	= KERN_SETUID_DUMPABLE,
 		.procname	= "suid_dumpable",
 		.data		= &suid_dumpable,

--

Re: [patch 3/9] unprivileged mounts: account user mounts

[Dave Hansen]

On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
> plain text document attachment
> (unprivileged-mounts-account-user-mounts.patch)
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Add sysctl variables for accounting and limiting the number of user
> mounts.
...
> +int nr_user_mounts;
> +int max_user_mounts = 1024;

Just from a containers point of view, I think this is something we'll
need to fix up in the near future if it stays in the current form.

Instead of having a global tracking, perhaps we could have a per-user
limit tracked in 'struct user'.  The plans are to ensure that two
containers' users "dave" each have a different 'struct user', so that
seems to be a decent place to track it.

Also, is a read-only sysctl really the best way to get the number of
user mounts back out of the kernel?  What would you use it for?

Do you need any special logic for setting 'max_user_mounts' in the case
where it gets set _below_ 'nr_user_mounts'?

>  /* /sys/fs */
>  struct kobject *fs_kobj;
>  EXPORT_SYMBOL_GPL(fs_kobj);
> @@ -477,11 +480,30 @@ static struct vfsmount *skip_mnt_tree(st
>  	return p;
>  }
> 
> +static void dec_nr_user_mounts(void)
> +{
> +	spin_lock(&vfsmount_lock);
> +	nr_user_mounts--;
> +	spin_unlock(&vfsmount_lock);
> +}
> +
>  static void set_mnt_user(struct vfsmount *mnt)
>  {
>  	BUG_ON(mnt->mnt_flags & MNT_USER);
>  	mnt->mnt_uid = current->fsuid;
>  	mnt->mnt_flags |= MNT_USER;
> +	spin_lock(&vfsmount_lock);
> +	nr_user_mounts++;
> +	spin_unlock(&vfsmount_lock);
> +}

One little nitpick on the patch layout:  It's a wee bit difficult to
audit how the set function is used vs the clear one when its users don't
come until the later patches.  It might be worth introducing the users
here, too.

> +static void clear_mnt_user(struct vfsmount *mnt)
> +{
> +	if (mnt->mnt_flags & MNT_USER) {
> +		mnt->mnt_uid = 0;
> +		mnt->mnt_flags &= ~MNT_USER;
> +		dec_nr_user_mounts();
> +	}
>  }
> 
>  static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
> @@ -542,6 +564,7 @@ static inline void __mntput(struct vfsmo
>  	 */
>  	WARN_ON(atomic_read(&mnt->__mnt_writers));
>  	dput(mnt->mnt_root);
> +	clear_mnt_user(mnt);
>  	free_vfsmnt(mnt);
>  	deactivate_super(sb);
>  }
> @@ -1306,6 +1329,7 @@ static int do_remount(struct nameidata *
>  	else
>  		err = do_remount_sb(sb, flags, data, 0);
>  	if (!err) {
> +		clear_mnt_user(nd->path.mnt);
>  		nd->path.mnt->mnt_flags = mnt_flags;
>  		if (flags & MS_SETUSER)
>  			set_mnt_user(nd->path.mnt);
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h	2008-01-03 20:52:38.000000000 +0100
> +++ linux/include/linux/fs.h	2008-01-03 21:15:35.000000000 +0100
> @@ -50,6 +50,9 @@ extern struct inodes_stat_t inodes_stat;
> 
>  extern int leases_enable, lease_break_time;
> 
> +extern int nr_user_mounts;
> +extern int max_user_mounts;
> +
>  #ifdef CONFIG_DNOTIFY
>  extern int dir_notify_enable;
>  #endif
> Index: linux/kernel/sysctl.c
> ===================================================================
> --- linux.orig/kernel/sysctl.c	2008-01-03 17:13:22.000000000 +0100
> +++ linux/kernel/sysctl.c	2008-01-03 21:15:35.000000000 +0100
> @@ -1288,6 +1288,22 @@ static struct ctl_table fs_table[] = {
>  #endif	
>  #endif
>  	{
> +		.ctl_name	= CTL_UNNUMBERED,
> +		.procname	= "nr_user_mounts",
> +		.data		= &nr_user_mounts,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0444,
> +		.proc_handler	= &proc_dointvec,
> +	},
> +	{
> +		.ctl_name	= CTL_UNNUMBERED,
> +		.procname	= "max_user_mounts",
> +		.data		= &max_user_mounts,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= &proc_dointvec,
> +	},
> +	{
>  		.ctl_name	= KERN_SETUID_DUMPABLE,
>  		.procname	= "suid_dumpable",
>  		.data		= &suid_dumpable,
> 
> --
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/containers
-- Dave

Re: [patch 3/9] unprivileged mounts: account user mounts

[Miklos Szeredi]

> On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
> > plain text document attachment
> > (unprivileged-mounts-account-user-mounts.patch)
> > From: Miklos Szeredi <mszeredi@suse.cz>
> > 
> > Add sysctl variables for accounting and limiting the number of user
> > mounts.
> ...
> > +int nr_user_mounts;
> > +int max_user_mounts = 1024;
> 
> Just from a containers point of view, I think this is something we'll
> need to fix up in the near future if it stays in the current form.
> 
> Instead of having a global tracking, perhaps we could have a per-user
> limit tracked in 'struct user'.  The plans are to ensure that two
> containers' users "dave" each have a different 'struct user', so that
> seems to be a decent place to track it.

At one time there was a per-user accounting patch, but it was dropped,
because it was deemed an unnecessary additional compexity.

max_user_mounts is analogue to files_stat.max_files (which is a sysctl
tunable also), and it's purpose is really to make sure that a user is
not able to create an insane number of mounts, and not to acurately
limit normal usage.

So I'm not sure a per-container or per-user count is really needed.

> Also, is a read-only sysctl really the best way to get the number of
> user mounts back out of the kernel?  What would you use it for?

Just to check, why I got that (EPERM or whatever) error for the mount
command.

> Do you need any special logic for setting 'max_user_mounts' in the case
> where it gets set _below_ 'nr_user_mounts'?

No, I don't think such corner cases really matter in this case.

> >  /* /sys/fs */
> >  struct kobject *fs_kobj;
> >  EXPORT_SYMBOL_GPL(fs_kobj);
> > @@ -477,11 +480,30 @@ static struct vfsmount *skip_mnt_tree(st
> >  	return p;
> >  }
> > 
> > +static void dec_nr_user_mounts(void)
> > +{
> > +	spin_lock(&vfsmount_lock);
> > +	nr_user_mounts--;
> > +	spin_unlock(&vfsmount_lock);
> > +}
> > +
> >  static void set_mnt_user(struct vfsmount *mnt)
> >  {
> >  	BUG_ON(mnt->mnt_flags & MNT_USER);
> >  	mnt->mnt_uid = current->fsuid;
> >  	mnt->mnt_flags |= MNT_USER;
> > +	spin_lock(&vfsmount_lock);
> > +	nr_user_mounts++;
> > +	spin_unlock(&vfsmount_lock);
> > +}
> 
> One little nitpick on the patch layout:  It's a wee bit difficult to
> audit how the set function is used vs the clear one when its users don't
> come until the later patches.  It might be worth introducing the users
> here, too.

Yeah, maybe some of the patches should be folded together.  If a
resubmit is necessary I'll look into that.

Miklos

Re: [patch 3/9] unprivileged mounts: account user mounts

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Add sysctl variables for accounting and limiting the number of user
> mounts.
> 
> The maximum number of user mounts is set to 1024 by default.  This
> won't in itself enable user mounts, setting a mount to be owned by a
> user is first needed
> 
> [akpm]
>  - don't use enumerated sysctls
> 
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Seems sane enough, given your responses to Dave.

Acked-by: Serge Hallyn <serue@us.ibm.com>

> ---
> 
> Index: linux/Documentation/filesystems/proc.txt
> ===================================================================
> --- linux.orig/Documentation/filesystems/proc.txt	2008-01-03 17:12:58.000000000 +0100
> +++ linux/Documentation/filesystems/proc.txt	2008-01-03 21:15:35.000000000 +0100
> @@ -1012,6 +1012,15 @@ reaches aio-max-nr then io_setup will fa
>  raising aio-max-nr does not result in the pre-allocation or re-sizing
>  of any kernel data structures.
> 
> +nr_user_mounts and max_user_mounts
> +----------------------------------
> +
> +These represent the number of "user" mounts and the maximum number of
> +"user" mounts respectively.  User mounts may be created by
> +unprivileged users.  User mounts may also be created with sysadmin
> +privileges on behalf of a user, in which case nr_user_mounts may
> +exceed max_user_mounts.
> +
>  2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
>  -----------------------------------------------------------
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-03 21:14:16.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-03 21:15:35.000000000 +0100
> @@ -44,6 +44,9 @@ static struct list_head *mount_hashtable
>  static struct kmem_cache *mnt_cache __read_mostly;
>  static struct rw_semaphore namespace_sem;
> 
> +int nr_user_mounts;
> +int max_user_mounts = 1024;
> +
>  /* /sys/fs */
>  struct kobject *fs_kobj;
>  EXPORT_SYMBOL_GPL(fs_kobj);
> @@ -477,11 +480,30 @@ static struct vfsmount *skip_mnt_tree(st
>  	return p;
>  }
> 
> +static void dec_nr_user_mounts(void)
> +{
> +	spin_lock(&vfsmount_lock);
> +	nr_user_mounts--;
> +	spin_unlock(&vfsmount_lock);
> +}
> +
>  static void set_mnt_user(struct vfsmount *mnt)
>  {
>  	BUG_ON(mnt->mnt_flags & MNT_USER);
>  	mnt->mnt_uid = current->fsuid;
>  	mnt->mnt_flags |= MNT_USER;
> +	spin_lock(&vfsmount_lock);
> +	nr_user_mounts++;
> +	spin_unlock(&vfsmount_lock);
> +}
> +
> +static void clear_mnt_user(struct vfsmount *mnt)
> +{
> +	if (mnt->mnt_flags & MNT_USER) {
> +		mnt->mnt_uid = 0;
> +		mnt->mnt_flags &= ~MNT_USER;
> +		dec_nr_user_mounts();
> +	}
>  }
> 
>  static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
> @@ -542,6 +564,7 @@ static inline void __mntput(struct vfsmo
>  	 */
>  	WARN_ON(atomic_read(&mnt->__mnt_writers));
>  	dput(mnt->mnt_root);
> +	clear_mnt_user(mnt);
>  	free_vfsmnt(mnt);
>  	deactivate_super(sb);
>  }
> @@ -1306,6 +1329,7 @@ static int do_remount(struct nameidata *
>  	else
>  		err = do_remount_sb(sb, flags, data, 0);
>  	if (!err) {
> +		clear_mnt_user(nd->path.mnt);
>  		nd->path.mnt->mnt_flags = mnt_flags;
>  		if (flags & MS_SETUSER)
>  			set_mnt_user(nd->path.mnt);
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h	2008-01-03 20:52:38.000000000 +0100
> +++ linux/include/linux/fs.h	2008-01-03 21:15:35.000000000 +0100
> @@ -50,6 +50,9 @@ extern struct inodes_stat_t inodes_stat;
> 
>  extern int leases_enable, lease_break_time;
> 
> +extern int nr_user_mounts;
> +extern int max_user_mounts;
> +
>  #ifdef CONFIG_DNOTIFY
>  extern int dir_notify_enable;
>  #endif
> Index: linux/kernel/sysctl.c
> ===================================================================
> --- linux.orig/kernel/sysctl.c	2008-01-03 17:13:22.000000000 +0100
> +++ linux/kernel/sysctl.c	2008-01-03 21:15:35.000000000 +0100
> @@ -1288,6 +1288,22 @@ static struct ctl_table fs_table[] = {
>  #endif	
>  #endif
>  	{
> +		.ctl_name	= CTL_UNNUMBERED,
> +		.procname	= "nr_user_mounts",
> +		.data		= &nr_user_mounts,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0444,
> +		.proc_handler	= &proc_dointvec,
> +	},
> +	{
> +		.ctl_name	= CTL_UNNUMBERED,
> +		.procname	= "max_user_mounts",
> +		.data		= &max_user_mounts,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= &proc_dointvec,
> +	},
> +	{
>  		.ctl_name	= KERN_SETUID_DUMPABLE,
>  		.procname	= "suid_dumpable",
>  		.data		= &suid_dumpable,
> 
> --

[patch 4/9] unprivileged mounts: propagate error values from clone_mnt

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-propagate-error-values-from-clone_mnt.patch --]
[-- Type: text/plain, Size: 5319 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Allow clone_mnt() to return errors other than ENOMEM.  This will be used for
returning a different error value when the number of user mounts goes over the
limit.

Fix copy_tree() to return EPERM for unbindable mounts.

Don't propagate further from dup_mnt_ns() as that copy_tree() can only fail
with -ENOMEM.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-04 13:47:09.000000000 +0100
+++ linux/fs/namespace.c	2008-01-04 13:47:49.000000000 +0100
@@ -512,41 +512,42 @@ static struct vfsmount *clone_mnt(struct
 	struct super_block *sb = old->mnt_sb;
 	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
 
-	if (mnt) {
-		mnt->mnt_flags = old->mnt_flags;
-		atomic_inc(&sb->s_active);
-		mnt->mnt_sb = sb;
-		mnt->mnt_root = dget(root);
-		mnt->mnt_mountpoint = mnt->mnt_root;
-		mnt->mnt_parent = mnt;
-
-		/* don't copy the MNT_USER flag */
-		mnt->mnt_flags &= ~MNT_USER;
-		if (flag & CL_SETUSER)
-			set_mnt_user(mnt);
-
-		if (flag & CL_SLAVE) {
-			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
-			mnt->mnt_master = old;
-			CLEAR_MNT_SHARED(mnt);
-		} else if (!(flag & CL_PRIVATE)) {
-			if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
-				list_add(&mnt->mnt_share, &old->mnt_share);
-			if (IS_MNT_SLAVE(old))
-				list_add(&mnt->mnt_slave, &old->mnt_slave);
-			mnt->mnt_master = old->mnt_master;
-		}
-		if (flag & CL_MAKE_SHARED)
-			set_mnt_shared(mnt);
+	if (!mnt)
+		return ERR_PTR(-ENOMEM);
 
-		/* stick the duplicate mount on the same expiry list
-		 * as the original if that was on one */
-		if (flag & CL_EXPIRE) {
-			spin_lock(&vfsmount_lock);
-			if (!list_empty(&old->mnt_expire))
-				list_add(&mnt->mnt_expire, &old->mnt_expire);
-			spin_unlock(&vfsmount_lock);
-		}
+	mnt->mnt_flags = old->mnt_flags;
+	atomic_inc(&sb->s_active);
+	mnt->mnt_sb = sb;
+	mnt->mnt_root = dget(root);
+	mnt->mnt_mountpoint = mnt->mnt_root;
+	mnt->mnt_parent = mnt;
+
+	/* don't copy the MNT_USER flag */
+	mnt->mnt_flags &= ~MNT_USER;
+	if (flag & CL_SETUSER)
+		set_mnt_user(mnt);
+
+	if (flag & CL_SLAVE) {
+		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
+		mnt->mnt_master = old;
+		CLEAR_MNT_SHARED(mnt);
+	} else if (!(flag & CL_PRIVATE)) {
+		if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
+			list_add(&mnt->mnt_share, &old->mnt_share);
+		if (IS_MNT_SLAVE(old))
+			list_add(&mnt->mnt_slave, &old->mnt_slave);
+		mnt->mnt_master = old->mnt_master;
+	}
+	if (flag & CL_MAKE_SHARED)
+		set_mnt_shared(mnt);
+
+	/* stick the duplicate mount on the same expiry list
+	 * as the original if that was on one */
+	if (flag & CL_EXPIRE) {
+		spin_lock(&vfsmount_lock);
+		if (!list_empty(&old->mnt_expire))
+			list_add(&mnt->mnt_expire, &old->mnt_expire);
+		spin_unlock(&vfsmount_lock);
 	}
 	return mnt;
 }
@@ -1021,11 +1022,11 @@ struct vfsmount *copy_tree(struct vfsmou
 	struct nameidata nd;
 
 	if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
-		return NULL;
+		return ERR_PTR(-EPERM);
 
 	res = q = clone_mnt(mnt, dentry, flag);
-	if (!q)
-		goto Enomem;
+	if (IS_ERR(q))
+		goto error;
 	q->mnt_mountpoint = mnt->mnt_mountpoint;
 
 	p = mnt;
@@ -1046,8 +1047,8 @@ struct vfsmount *copy_tree(struct vfsmou
 			nd.path.mnt = q;
 			nd.path.dentry = p->mnt_mountpoint;
 			q = clone_mnt(p, p->mnt_root, flag);
-			if (!q)
-				goto Enomem;
+			if (IS_ERR(q))
+				goto error;
 			spin_lock(&vfsmount_lock);
 			list_add_tail(&q->mnt_list, &res->mnt_list);
 			attach_mnt(q, &nd);
@@ -1055,7 +1056,7 @@ struct vfsmount *copy_tree(struct vfsmou
 		}
 	}
 	return res;
-Enomem:
+ error:
 	if (res) {
 		LIST_HEAD(umount_list);
 		spin_lock(&vfsmount_lock);
@@ -1063,7 +1064,7 @@ Enomem:
 		spin_unlock(&vfsmount_lock);
 		release_mounts(&umount_list);
 	}
-	return NULL;
+	return q;
 }
 
 struct vfsmount *collect_mounts(struct vfsmount *mnt, struct dentry *dentry)
@@ -1262,13 +1263,13 @@ static int do_loopback(struct nameidata 
 		goto out;
 
 	clone_fl = (flags & MS_SETUSER) ? CL_SETUSER : 0;
-	err = -ENOMEM;
 	if (flags & MS_REC)
 		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
 	else
 		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
 
-	if (!mnt)
+	err = PTR_ERR(mnt);
+	if (IS_ERR(mnt))
 		goto out;
 
 	err = graft_tree(mnt, nd);
@@ -1840,7 +1841,7 @@ static struct mnt_namespace *dup_mnt_ns(
 	/* First pass: copy the tree topology */
 	new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
 					CL_COPY_ALL | CL_EXPIRE);
-	if (!new_ns->root) {
+	if (IS_ERR(new_ns->root)) {
 		up_write(&namespace_sem);
 		kfree(new_ns);
 		return ERR_PTR(-ENOMEM);;
Index: linux/fs/pnode.c
===================================================================
--- linux.orig/fs/pnode.c	2008-01-04 13:45:46.000000000 +0100
+++ linux/fs/pnode.c	2008-01-04 13:47:49.000000000 +0100
@@ -189,8 +189,9 @@ int propagate_mnt(struct vfsmount *dest_
 
 		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 
-		if (!(child = copy_tree(source, source->mnt_root, type))) {
-			ret = -ENOMEM;
+		child = copy_tree(source, source->mnt_root, type);
+		if (IS_ERR(child)) {
+			ret = PTR_ERR(child);
 			list_splice(tree_list, tmp_list.prev);
 			goto out;
 		}

--

Re: [patch 4/9] unprivileged mounts: propagate error values from clone_mnt

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Allow clone_mnt() to return errors other than ENOMEM.  This will be used for
> returning a different error value when the number of user mounts goes over the
> limit.
> 
> Fix copy_tree() to return EPERM for unbindable mounts.
> 
> Don't propagate further from dup_mnt_ns() as that copy_tree() can only fail
> with -ENOMEM.

I see what you're saying, but it just seems like it's bound to be more
confusing this way.

What's the reason to insist on doing this?  To force people to think
about it as a form of documentation?

Still,

> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Acked-by: Serge Hallyn <serue@us.ibm.com>

> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-04 13:47:09.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-04 13:47:49.000000000 +0100
> @@ -512,41 +512,42 @@ static struct vfsmount *clone_mnt(struct
>  	struct super_block *sb = old->mnt_sb;
>  	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
> 
> -	if (mnt) {
> -		mnt->mnt_flags = old->mnt_flags;
> -		atomic_inc(&sb->s_active);
> -		mnt->mnt_sb = sb;
> -		mnt->mnt_root = dget(root);
> -		mnt->mnt_mountpoint = mnt->mnt_root;
> -		mnt->mnt_parent = mnt;
> -
> -		/* don't copy the MNT_USER flag */
> -		mnt->mnt_flags &= ~MNT_USER;
> -		if (flag & CL_SETUSER)
> -			set_mnt_user(mnt);
> -
> -		if (flag & CL_SLAVE) {
> -			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
> -			mnt->mnt_master = old;
> -			CLEAR_MNT_SHARED(mnt);
> -		} else if (!(flag & CL_PRIVATE)) {
> -			if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
> -				list_add(&mnt->mnt_share, &old->mnt_share);
> -			if (IS_MNT_SLAVE(old))
> -				list_add(&mnt->mnt_slave, &old->mnt_slave);
> -			mnt->mnt_master = old->mnt_master;
> -		}
> -		if (flag & CL_MAKE_SHARED)
> -			set_mnt_shared(mnt);
> +	if (!mnt)
> +		return ERR_PTR(-ENOMEM);
> 
> -		/* stick the duplicate mount on the same expiry list
> -		 * as the original if that was on one */
> -		if (flag & CL_EXPIRE) {
> -			spin_lock(&vfsmount_lock);
> -			if (!list_empty(&old->mnt_expire))
> -				list_add(&mnt->mnt_expire, &old->mnt_expire);
> -			spin_unlock(&vfsmount_lock);
> -		}
> +	mnt->mnt_flags = old->mnt_flags;
> +	atomic_inc(&sb->s_active);
> +	mnt->mnt_sb = sb;
> +	mnt->mnt_root = dget(root);
> +	mnt->mnt_mountpoint = mnt->mnt_root;
> +	mnt->mnt_parent = mnt;
> +
> +	/* don't copy the MNT_USER flag */
> +	mnt->mnt_flags &= ~MNT_USER;
> +	if (flag & CL_SETUSER)
> +		set_mnt_user(mnt);
> +
> +	if (flag & CL_SLAVE) {
> +		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
> +		mnt->mnt_master = old;
> +		CLEAR_MNT_SHARED(mnt);
> +	} else if (!(flag & CL_PRIVATE)) {
> +		if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
> +			list_add(&mnt->mnt_share, &old->mnt_share);
> +		if (IS_MNT_SLAVE(old))
> +			list_add(&mnt->mnt_slave, &old->mnt_slave);
> +		mnt->mnt_master = old->mnt_master;
> +	}
> +	if (flag & CL_MAKE_SHARED)
> +		set_mnt_shared(mnt);
> +
> +	/* stick the duplicate mount on the same expiry list
> +	 * as the original if that was on one */
> +	if (flag & CL_EXPIRE) {
> +		spin_lock(&vfsmount_lock);
> +		if (!list_empty(&old->mnt_expire))
> +			list_add(&mnt->mnt_expire, &old->mnt_expire);
> +		spin_unlock(&vfsmount_lock);
>  	}
>  	return mnt;
>  }
> @@ -1021,11 +1022,11 @@ struct vfsmount *copy_tree(struct vfsmou
>  	struct nameidata nd;
> 
>  	if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
> -		return NULL;
> +		return ERR_PTR(-EPERM);
> 
>  	res = q = clone_mnt(mnt, dentry, flag);
> -	if (!q)
> -		goto Enomem;
> +	if (IS_ERR(q))
> +		goto error;
>  	q->mnt_mountpoint = mnt->mnt_mountpoint;
> 
>  	p = mnt;
> @@ -1046,8 +1047,8 @@ struct vfsmount *copy_tree(struct vfsmou
>  			nd.path.mnt = q;
>  			nd.path.dentry = p->mnt_mountpoint;
>  			q = clone_mnt(p, p->mnt_root, flag);
> -			if (!q)
> -				goto Enomem;
> +			if (IS_ERR(q))
> +				goto error;
>  			spin_lock(&vfsmount_lock);
>  			list_add_tail(&q->mnt_list, &res->mnt_list);
>  			attach_mnt(q, &nd);
> @@ -1055,7 +1056,7 @@ struct vfsmount *copy_tree(struct vfsmou
>  		}
>  	}
>  	return res;
> -Enomem:
> + error:
>  	if (res) {
>  		LIST_HEAD(umount_list);
>  		spin_lock(&vfsmount_lock);
> @@ -1063,7 +1064,7 @@ Enomem:
>  		spin_unlock(&vfsmount_lock);
>  		release_mounts(&umount_list);
>  	}
> -	return NULL;
> +	return q;
>  }
> 
>  struct vfsmount *collect_mounts(struct vfsmount *mnt, struct dentry *dentry)
> @@ -1262,13 +1263,13 @@ static int do_loopback(struct nameidata 
>  		goto out;
> 
>  	clone_fl = (flags & MS_SETUSER) ? CL_SETUSER : 0;
> -	err = -ENOMEM;
>  	if (flags & MS_REC)
>  		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
>  	else
>  		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
> 
> -	if (!mnt)
> +	err = PTR_ERR(mnt);
> +	if (IS_ERR(mnt))
>  		goto out;
> 
>  	err = graft_tree(mnt, nd);
> @@ -1840,7 +1841,7 @@ static struct mnt_namespace *dup_mnt_ns(
>  	/* First pass: copy the tree topology */
>  	new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
>  					CL_COPY_ALL | CL_EXPIRE);
> -	if (!new_ns->root) {
> +	if (IS_ERR(new_ns->root)) {
>  		up_write(&namespace_sem);
>  		kfree(new_ns);
>  		return ERR_PTR(-ENOMEM);;
> Index: linux/fs/pnode.c
> ===================================================================
> --- linux.orig/fs/pnode.c	2008-01-04 13:45:46.000000000 +0100
> +++ linux/fs/pnode.c	2008-01-04 13:47:49.000000000 +0100
> @@ -189,8 +189,9 @@ int propagate_mnt(struct vfsmount *dest_
> 
>  		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
> 
> -		if (!(child = copy_tree(source, source->mnt_root, type))) {
> -			ret = -ENOMEM;
> +		child = copy_tree(source, source->mnt_root, type);
> +		if (IS_ERR(child)) {
> +			ret = PTR_ERR(child);
>  			list_splice(tree_list, tmp_list.prev);
>  			goto out;
>  		}
> 
> --
> -
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [patch 4/9] unprivileged mounts: propagate error values from clone_mnt

[Miklos Szeredi]

> Quoting Miklos Szeredi (miklos@szeredi.hu):
> > From: Miklos Szeredi <mszeredi@suse.cz>
> > 
> > Allow clone_mnt() to return errors other than ENOMEM.  This will be used for
> > returning a different error value when the number of user mounts goes over the
> > limit.
> > 
> > Fix copy_tree() to return EPERM for unbindable mounts.
> > 
> > Don't propagate further from dup_mnt_ns() as that copy_tree() can only fail
> > with -ENOMEM.
> 
> I see what you're saying, but it just seems like it's bound to be more
> confusing this way.

Ah yes, this is indeed confusing.  Last time dup_mnt_ns() returned a
namespace pointer or NULL.  But now I see it returns an ERR_PTR(error)
instead, which means it's cleaner to just propagate the error value.
I'll fix this.

Thanks,
Miklos

[patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-allow-unprivileged-bind-mounts.patch --]
[-- Type: text/plain, Size: 4004 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Allow bind mounts to unprivileged users if the following conditions are met:

  - mountpoint is not a symlink
  - parent mount is owned by the user
  - the number of user mounts is below the maximum

Unprivileged mounts imply MS_SETUSER, and will also have the "nosuid" and
"nodev" mount flags set.

In particular, if mounting process doesn't have CAP_SETUID capability,
then the "nosuid" flag will be added, and if it doesn't have CAP_MKNOD
capability, then the "nodev" flag will be added.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-04 13:47:49.000000000 +0100
+++ linux/fs/namespace.c	2008-01-04 13:48:01.000000000 +0100
@@ -487,11 +487,34 @@ static void dec_nr_user_mounts(void)
 	spin_unlock(&vfsmount_lock);
 }
 
-static void set_mnt_user(struct vfsmount *mnt)
+static int reserve_user_mount(void)
+{
+	int err = 0;
+
+	spin_lock(&vfsmount_lock);
+	if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
+		err = -EPERM;
+	else
+		nr_user_mounts++;
+	spin_unlock(&vfsmount_lock);
+	return err;
+}
+
+static void __set_mnt_user(struct vfsmount *mnt)
 {
 	BUG_ON(mnt->mnt_flags & MNT_USER);
 	mnt->mnt_uid = current->fsuid;
 	mnt->mnt_flags |= MNT_USER;
+
+	if (!capable(CAP_SETUID))
+		mnt->mnt_flags |= MNT_NOSUID;
+	if (!capable(CAP_MKNOD))
+		mnt->mnt_flags |= MNT_NODEV;
+}
+
+static void set_mnt_user(struct vfsmount *mnt)
+{
+	__set_mnt_user(mnt);
 	spin_lock(&vfsmount_lock);
 	nr_user_mounts++;
 	spin_unlock(&vfsmount_lock);
@@ -510,10 +533,16 @@ static struct vfsmount *clone_mnt(struct
 					int flag)
 {
 	struct super_block *sb = old->mnt_sb;
-	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
+	struct vfsmount *mnt;
 
+	if (flag & CL_SETUSER) {
+		int err = reserve_user_mount();
+		if (err)
+			return ERR_PTR(err);
+	}
+	mnt = alloc_vfsmnt(old->mnt_devname);
 	if (!mnt)
-		return ERR_PTR(-ENOMEM);
+		goto alloc_failed;
 
 	mnt->mnt_flags = old->mnt_flags;
 	atomic_inc(&sb->s_active);
@@ -525,7 +554,7 @@ static struct vfsmount *clone_mnt(struct
 	/* don't copy the MNT_USER flag */
 	mnt->mnt_flags &= ~MNT_USER;
 	if (flag & CL_SETUSER)
-		set_mnt_user(mnt);
+		__set_mnt_user(mnt);
 
 	if (flag & CL_SLAVE) {
 		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
@@ -550,6 +579,11 @@ static struct vfsmount *clone_mnt(struct
 		spin_unlock(&vfsmount_lock);
 	}
 	return mnt;
+
+ alloc_failed:
+	if (flag & CL_SETUSER)
+		dec_nr_user_mounts();
+	return ERR_PTR(-ENOMEM);
 }
 
 static inline void __mntput(struct vfsmount *mnt)
@@ -986,22 +1020,26 @@ asmlinkage long sys_oldumount(char __use
 
 #endif
 
-static int mount_is_safe(struct nameidata *nd)
+/*
+ * Conditions for unprivileged mounts are:
+ * - mountpoint is not a symlink
+ * - mountpoint is in a mount owned by the user
+ */
+static bool permit_mount(struct nameidata *nd, int *flags)
 {
+	struct inode *inode = nd->path.dentry->d_inode;
+
 	if (capable(CAP_SYS_ADMIN))
-		return 0;
-	return -EPERM;
-#ifdef notyet
-	if (S_ISLNK(nd->path.dentry->d_inode->i_mode))
-		return -EPERM;
-	if (nd->path.dentry->d_inode->i_mode & S_ISVTX) {
-		if (current->uid != nd->path.dentry->d_inode->i_uid)
-			return -EPERM;
-	}
-	if (vfs_permission(nd, MAY_WRITE))
-		return -EPERM;
-	return 0;
-#endif
+		return true;
+
+	if (S_ISLNK(inode->i_mode))
+		return false;
+
+	if (!is_mount_owner(nd->path.mnt, current->fsuid))
+		return false;
+
+	*flags |= MS_SETUSER;
+	return true;
 }
 
 static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
@@ -1245,9 +1283,10 @@ static int do_loopback(struct nameidata 
 	int clone_fl;
 	struct nameidata old_nd;
 	struct vfsmount *mnt = NULL;
-	int err = mount_is_safe(nd);
-	if (err)
-		return err;
+	int err;
+
+	if (!permit_mount(nd, &flags))
+		return -EPERM;
 	if (!old_name || !*old_name)
 		return -EINVAL;
 	err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);

--

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Dave Hansen]

On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
> +static int reserve_user_mount(void)
> +{
> +       int err = 0;
> +
> +       spin_lock(&vfsmount_lock);
> +       if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
> +               err = -EPERM;
> +       else
> +               nr_user_mounts++;
> +       spin_unlock(&vfsmount_lock);
> +       return err;
> +} 

Would -ENOSPC or -ENOMEM be a more descriptive error here?  

-- Dave

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Miklos Szeredi]

> On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
> > +static int reserve_user_mount(void)
> > +{
> > +       int err = 0;
> > +
> > +       spin_lock(&vfsmount_lock);
> > +       if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
> > +               err = -EPERM;
> > +       else
> > +               nr_user_mounts++;
> > +       spin_unlock(&vfsmount_lock);
> > +       return err;
> > +} 
> 
> Would -ENOSPC or -ENOMEM be a more descriptive error here?  

The logic behind EPERM, is that this failure is only for unprivileged
callers.  ENOMEM is too specifically about OOM.  It could be changed
to ENOSPC, ENFILE, EMFILE, or it could remain EPERM.  What do others
think?

Miklos

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Dave Hansen]

On Tue, 2008-01-08 at 20:08 +0100, Miklos Szeredi wrote:
> 
> The logic behind EPERM, is that this failure is only for unprivileged
> callers.  ENOMEM is too specifically about OOM.  It could be changed
> to ENOSPC, ENFILE, EMFILE, or it could remain EPERM.  What do others
> think? 

Since you're patching mount anyway, maybe you could add a little pointer
for people to go check the sysctl if they get a certain error code back
from here.

-- Dave

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Szabolcs Szakacsits]

On Tue, 8 Jan 2008, Miklos Szeredi wrote:
> > On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
> > > +static int reserve_user_mount(void)
> > > +{
> > > +       int err = 0;
> > > +
> > > +       spin_lock(&vfsmount_lock);
> > > +       if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
> > > +               err = -EPERM;
> > > +       else
> > > +               nr_user_mounts++;
> > > +       spin_unlock(&vfsmount_lock);
> > > +       return err;
> > > +} 
> > 
> > Would -ENOSPC or -ENOMEM be a more descriptive error here?  
> 
> The logic behind EPERM, is that this failure is only for unprivileged
> callers.  ENOMEM is too specifically about OOM.  It could be changed
> to ENOSPC, ENFILE, EMFILE, or it could remain EPERM.  What do others
> think?

I think it would be important to log the non-trivial errors. Several 
mount(8) hints to check for the reason by dmesg since it's already too 
challanging to figure out what's exactly the problem by the errno value. 
This could also prevent to mislead troubleshooters with the mount/sysctl 
race.

	Szaka

-- 
NTFS-3G:  http://ntfs-3g.org

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Jan Engelhardt]

On Jan 8 2008 20:08, Miklos Szeredi wrote:
>> On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
>> > +static int reserve_user_mount(void)
>> > +{
>> > +       int err = 0;
>> > +
>> > +       spin_lock(&vfsmount_lock);
>> > +       if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
>> > +               err = -EPERM;
>> > +       else
>> > +               nr_user_mounts++;
>> > +       spin_unlock(&vfsmount_lock);
>> > +       return err;
>> > +} 
>> 
>> Would -ENOSPC or -ENOMEM be a more descriptive error here?  
>
>The logic behind EPERM, is that this failure is only for unprivileged
>callers.  ENOMEM is too specifically about OOM.  It could be changed
>to ENOSPC, ENFILE, EMFILE, or it could remain EPERM.  What do others
>think?

ENOSPC: No space remaining on device => 'wth'.
ENOMEM: I usually think of a userspace OOM (e.g. malloc'ed out all of your
32-bit address space on 32-bit processes)
EMFILE: "Too many open files"
ENFILE: "Too many open files in system".

ENFILE seems like a temporary winner among these four.

Back in the old days, when the number of mounts was limited in Linux,
what error value did it return? That one could be used.

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Karel Zak]

On Wed, Jan 09, 2008 at 01:45:09PM +0100, Jan Engelhardt wrote:
> 
> On Jan 8 2008 20:08, Miklos Szeredi wrote:
> >> On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
> >> > +static int reserve_user_mount(void)
> >> > +{
> >> > +       int err = 0;
> >> > +
> >> > +       spin_lock(&vfsmount_lock);
> >> > +       if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
> >> > +               err = -EPERM;
> >> > +       else
> >> > +               nr_user_mounts++;
> >> > +       spin_unlock(&vfsmount_lock);
> >> > +       return err;
> >> > +} 
> >> 
> >> Would -ENOSPC or -ENOMEM be a more descriptive error here?  
> >
> >The logic behind EPERM, is that this failure is only for unprivileged
> >callers.  ENOMEM is too specifically about OOM.  It could be changed
> >to ENOSPC, ENFILE, EMFILE, or it could remain EPERM.  What do others
> >think?
> 
> ENOSPC: No space remaining on device => 'wth'.
> ENOMEM: I usually think of a userspace OOM (e.g. malloc'ed out all of your
> 32-bit address space on 32-bit processes)
> EMFILE: "Too many open files"
> ENFILE: "Too many open files in system".
> 
> ENFILE seems like a temporary winner among these four.

 I see "EMFILE", it's still supported by the latest mount(8).

> Back in the old days, when the number of mounts was limited in Linux,
> what error value did it return? That one could be used.

 Copy & past from mount-0.99.2:

  /* Mount failed, complain, but don't die.  */
  switch (mnt_err)
    {
    case EPERM:
      if (geteuid() == 0)
	error ("mount: mount point %s is not a directory", node);
      else
	error ("mount: must be superuser to use mount");
      break;
    case EBUSY:
      error ("mount: wrong fs type, %s already mounted, %s busy, "
	"or other error", spec, node);
      break;
    case ENOENT:
      error ("mount: mount point %s does not exist", node); break;
    case ENOTDIR:
      error ("mount: mount point %s is not a directory", node); break;
    case EINVAL:
      error ("mount: %s not a mount point", spec); break;
    case EMFILE:
      error ("mount table full"); break;
    case EIO:
      error ("mount: %s: can't read superblock", spec); break;
    case ENODEV:
      error ("mount: fs type %s not supported by kernel", type); break;
    case ENOTBLK:
      error ("mount: %s is not a block device", spec); break;
    case ENXIO:
      error ("mount: %s is not a valid block device", spec); break;
    case EACCES:
      error ("mount: block device %s is not permitted on its filesystem", spec);
      break;
    default:
      error ("mount: %s", strerror (mnt_err)); break;
    }


  Karel

-- 
 Karel Zak  <kzak@redhat.com>

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Miklos Szeredi]

>     case EMFILE:
>       error ("mount table full"); break;

OK, we could go with EMFILE, but the message should be changed to
something like "maximum unprivileged mount count exceeded".

Miklos

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Dave Hansen]

On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
> @@ -510,10 +533,16 @@ static struct vfsmount *clone_mnt(struct
>                                         int flag)
>  {
>         struct super_block *sb = old->mnt_sb;
> -       struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
> +       struct vfsmount *mnt;
> 
> +       if (flag & CL_SETUSER) {
> +               int err = reserve_user_mount();
> +               if (err)
> +                       return ERR_PTR(err);
> +       }
> +       mnt = alloc_vfsmnt(old->mnt_devname);
>         if (!mnt)
> -               return ERR_PTR(-ENOMEM);
> +               goto alloc_failed;
> 
>         mnt->mnt_flags = old->mnt_flags;
>         atomic_inc(&sb->s_active); 

I think there's a little race here.  We could have several users racing
to get to this point when nr_user_mounts==max_user_mounts-1.  One user
wins the race and gets their mount reserved.  The others get the error
out of reserve_user_mount(), and return.

But, the winner goes on to error out on some condition further down in
clone_mnt() and never actually instantiates the mount.

Do you think this is a problem?

I think just about the one solution is to block new mounters on a
sleepable lock until the race winner actually finishes their mount
operation.  

-- Dave

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Miklos Szeredi]

> > @@ -510,10 +533,16 @@ static struct vfsmount *clone_mnt(struct
> >                                         int flag)
> >  {
> >         struct super_block *sb = old->mnt_sb;
> > -       struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
> > +       struct vfsmount *mnt;
> > 
> > +       if (flag & CL_SETUSER) {
> > +               int err = reserve_user_mount();
> > +               if (err)
> > +                       return ERR_PTR(err);
> > +       }
> > +       mnt = alloc_vfsmnt(old->mnt_devname);
> >         if (!mnt)
> > -               return ERR_PTR(-ENOMEM);
> > +               goto alloc_failed;
> > 
> >         mnt->mnt_flags = old->mnt_flags;
> >         atomic_inc(&sb->s_active); 
> 
> I think there's a little race here.  We could have several users racing
> to get to this point when nr_user_mounts==max_user_mounts-1.  One user
> wins the race and gets their mount reserved.  The others get the error
> out of reserve_user_mount(), and return.
> 
> But, the winner goes on to error out on some condition further down in
> clone_mnt() and never actually instantiates the mount.
> 
> Do you think this is a problem?

For similar reasons as stated in the previous mail, I don't think this
matters.  If nr_user_mounts is getting remotely close to
max_user_mounts, then something is wrong (or the max needs to be
raised anyway).

Thanks for the review, Dave!

Miklos

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Allow bind mounts to unprivileged users if the following conditions are met:
> 
>   - mountpoint is not a symlink
>   - parent mount is owned by the user
>   - the number of user mounts is below the maximum
> 
> Unprivileged mounts imply MS_SETUSER, and will also have the "nosuid" and
> "nodev" mount flags set.
> 
> In particular, if mounting process doesn't have CAP_SETUID capability,
> then the "nosuid" flag will be added, and if it doesn't have CAP_MKNOD
> capability, then the "nodev" flag will be added.

That little part by itself is really needed in order to make the ability
to remove CAP_MKNOD from a process tree's bounding set meaningful.
Else instead of creating /dev/hda1, the user can just mount a filesystem
with hda1 existing on it.  (Which is why I was surprised when one day
I found this code missing :)

But of course I'm a fan of the patchset altogether.  I plan to review in
more detail early next week, but since I liked the previous submission I
don't see myself having any complaints, so I'm glad to see the reviews
by others.

thanks,
-serge

> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-04 13:47:49.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-04 13:48:01.000000000 +0100
> @@ -487,11 +487,34 @@ static void dec_nr_user_mounts(void)
>  	spin_unlock(&vfsmount_lock);
>  }
> 
> -static void set_mnt_user(struct vfsmount *mnt)
> +static int reserve_user_mount(void)
> +{
> +	int err = 0;
> +
> +	spin_lock(&vfsmount_lock);
> +	if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
> +		err = -EPERM;
> +	else
> +		nr_user_mounts++;
> +	spin_unlock(&vfsmount_lock);
> +	return err;
> +}
> +
> +static void __set_mnt_user(struct vfsmount *mnt)
>  {
>  	BUG_ON(mnt->mnt_flags & MNT_USER);
>  	mnt->mnt_uid = current->fsuid;
>  	mnt->mnt_flags |= MNT_USER;
> +
> +	if (!capable(CAP_SETUID))
> +		mnt->mnt_flags |= MNT_NOSUID;
> +	if (!capable(CAP_MKNOD))
> +		mnt->mnt_flags |= MNT_NODEV;
> +}
> +
> +static void set_mnt_user(struct vfsmount *mnt)
> +{
> +	__set_mnt_user(mnt);
>  	spin_lock(&vfsmount_lock);
>  	nr_user_mounts++;
>  	spin_unlock(&vfsmount_lock);
> @@ -510,10 +533,16 @@ static struct vfsmount *clone_mnt(struct
>  					int flag)
>  {
>  	struct super_block *sb = old->mnt_sb;
> -	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
> +	struct vfsmount *mnt;
> 
> +	if (flag & CL_SETUSER) {
> +		int err = reserve_user_mount();
> +		if (err)
> +			return ERR_PTR(err);
> +	}
> +	mnt = alloc_vfsmnt(old->mnt_devname);
>  	if (!mnt)
> -		return ERR_PTR(-ENOMEM);
> +		goto alloc_failed;
> 
>  	mnt->mnt_flags = old->mnt_flags;
>  	atomic_inc(&sb->s_active);
> @@ -525,7 +554,7 @@ static struct vfsmount *clone_mnt(struct
>  	/* don't copy the MNT_USER flag */
>  	mnt->mnt_flags &= ~MNT_USER;
>  	if (flag & CL_SETUSER)
> -		set_mnt_user(mnt);
> +		__set_mnt_user(mnt);
> 
>  	if (flag & CL_SLAVE) {
>  		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
> @@ -550,6 +579,11 @@ static struct vfsmount *clone_mnt(struct
>  		spin_unlock(&vfsmount_lock);
>  	}
>  	return mnt;
> +
> + alloc_failed:
> +	if (flag & CL_SETUSER)
> +		dec_nr_user_mounts();
> +	return ERR_PTR(-ENOMEM);
>  }
> 
>  static inline void __mntput(struct vfsmount *mnt)
> @@ -986,22 +1020,26 @@ asmlinkage long sys_oldumount(char __use
> 
>  #endif
> 
> -static int mount_is_safe(struct nameidata *nd)
> +/*
> + * Conditions for unprivileged mounts are:
> + * - mountpoint is not a symlink
> + * - mountpoint is in a mount owned by the user
> + */
> +static bool permit_mount(struct nameidata *nd, int *flags)
>  {
> +	struct inode *inode = nd->path.dentry->d_inode;
> +
>  	if (capable(CAP_SYS_ADMIN))
> -		return 0;
> -	return -EPERM;
> -#ifdef notyet
> -	if (S_ISLNK(nd->path.dentry->d_inode->i_mode))
> -		return -EPERM;
> -	if (nd->path.dentry->d_inode->i_mode & S_ISVTX) {
> -		if (current->uid != nd->path.dentry->d_inode->i_uid)
> -			return -EPERM;
> -	}
> -	if (vfs_permission(nd, MAY_WRITE))
> -		return -EPERM;
> -	return 0;
> -#endif
> +		return true;
> +
> +	if (S_ISLNK(inode->i_mode))
> +		return false;
> +
> +	if (!is_mount_owner(nd->path.mnt, current->fsuid))
> +		return false;
> +
> +	*flags |= MS_SETUSER;
> +	return true;
>  }
> 
>  static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
> @@ -1245,9 +1283,10 @@ static int do_loopback(struct nameidata 
>  	int clone_fl;
>  	struct nameidata old_nd;
>  	struct vfsmount *mnt = NULL;
> -	int err = mount_is_safe(nd);
> -	if (err)
> -		return err;
> +	int err;
> +
> +	if (!permit_mount(nd, &flags))
> +		return -EPERM;
>  	if (!old_name || !*old_name)
>  		return -EINVAL;
>  	err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
> 
> --

Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Allow bind mounts to unprivileged users if the following conditions are met:
> 
>   - mountpoint is not a symlink
>   - parent mount is owned by the user
>   - the number of user mounts is below the maximum
> 
> Unprivileged mounts imply MS_SETUSER, and will also have the "nosuid" and
> "nodev" mount flags set.
> 
> In particular, if mounting process doesn't have CAP_SETUID capability,
> then the "nosuid" flag will be added, and if it doesn't have CAP_MKNOD
> capability, then the "nodev" flag will be added.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Acked-by: Serge Hallyn <serue@us.ibm.com>

> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-04 13:47:49.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-04 13:48:01.000000000 +0100
> @@ -487,11 +487,34 @@ static void dec_nr_user_mounts(void)
>  	spin_unlock(&vfsmount_lock);
>  }
> 
> -static void set_mnt_user(struct vfsmount *mnt)
> +static int reserve_user_mount(void)
> +{
> +	int err = 0;
> +
> +	spin_lock(&vfsmount_lock);
> +	if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
> +		err = -EPERM;
> +	else
> +		nr_user_mounts++;
> +	spin_unlock(&vfsmount_lock);
> +	return err;
> +}
> +
> +static void __set_mnt_user(struct vfsmount *mnt)
>  {
>  	BUG_ON(mnt->mnt_flags & MNT_USER);
>  	mnt->mnt_uid = current->fsuid;
>  	mnt->mnt_flags |= MNT_USER;
> +
> +	if (!capable(CAP_SETUID))
> +		mnt->mnt_flags |= MNT_NOSUID;
> +	if (!capable(CAP_MKNOD))
> +		mnt->mnt_flags |= MNT_NODEV;
> +}
> +
> +static void set_mnt_user(struct vfsmount *mnt)
> +{
> +	__set_mnt_user(mnt);
>  	spin_lock(&vfsmount_lock);
>  	nr_user_mounts++;
>  	spin_unlock(&vfsmount_lock);
> @@ -510,10 +533,16 @@ static struct vfsmount *clone_mnt(struct
>  					int flag)
>  {
>  	struct super_block *sb = old->mnt_sb;
> -	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
> +	struct vfsmount *mnt;
> 
> +	if (flag & CL_SETUSER) {
> +		int err = reserve_user_mount();
> +		if (err)
> +			return ERR_PTR(err);
> +	}
> +	mnt = alloc_vfsmnt(old->mnt_devname);
>  	if (!mnt)
> -		return ERR_PTR(-ENOMEM);
> +		goto alloc_failed;
> 
>  	mnt->mnt_flags = old->mnt_flags;
>  	atomic_inc(&sb->s_active);
> @@ -525,7 +554,7 @@ static struct vfsmount *clone_mnt(struct
>  	/* don't copy the MNT_USER flag */
>  	mnt->mnt_flags &= ~MNT_USER;
>  	if (flag & CL_SETUSER)
> -		set_mnt_user(mnt);
> +		__set_mnt_user(mnt);
> 
>  	if (flag & CL_SLAVE) {
>  		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
> @@ -550,6 +579,11 @@ static struct vfsmount *clone_mnt(struct
>  		spin_unlock(&vfsmount_lock);
>  	}
>  	return mnt;
> +
> + alloc_failed:
> +	if (flag & CL_SETUSER)
> +		dec_nr_user_mounts();
> +	return ERR_PTR(-ENOMEM);
>  }
> 
>  static inline void __mntput(struct vfsmount *mnt)
> @@ -986,22 +1020,26 @@ asmlinkage long sys_oldumount(char __use
> 
>  #endif
> 
> -static int mount_is_safe(struct nameidata *nd)
> +/*
> + * Conditions for unprivileged mounts are:
> + * - mountpoint is not a symlink
> + * - mountpoint is in a mount owned by the user
> + */
> +static bool permit_mount(struct nameidata *nd, int *flags)
>  {
> +	struct inode *inode = nd->path.dentry->d_inode;
> +
>  	if (capable(CAP_SYS_ADMIN))
> -		return 0;
> -	return -EPERM;
> -#ifdef notyet
> -	if (S_ISLNK(nd->path.dentry->d_inode->i_mode))
> -		return -EPERM;
> -	if (nd->path.dentry->d_inode->i_mode & S_ISVTX) {
> -		if (current->uid != nd->path.dentry->d_inode->i_uid)
> -			return -EPERM;
> -	}
> -	if (vfs_permission(nd, MAY_WRITE))
> -		return -EPERM;
> -	return 0;
> -#endif
> +		return true;
> +
> +	if (S_ISLNK(inode->i_mode))
> +		return false;
> +
> +	if (!is_mount_owner(nd->path.mnt, current->fsuid))
> +		return false;
> +
> +	*flags |= MS_SETUSER;
> +	return true;
>  }
> 
>  static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
> @@ -1245,9 +1283,10 @@ static int do_loopback(struct nameidata 
>  	int clone_fl;
>  	struct nameidata old_nd;
>  	struct vfsmount *mnt = NULL;
> -	int err = mount_is_safe(nd);
> -	if (err)
> -		return err;
> +	int err;
> +
> +	if (!permit_mount(nd, &flags))
> +		return -EPERM;
>  	if (!old_name || !*old_name)
>  		return -EINVAL;
>  	err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
> 
> --

[patch 6/9] unprivileged mounts: allow unprivileged mounts

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-allow-unprivileged-mounts.patch --]
[-- Type: text/plain, Size: 6018 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Define a new fs flag FS_SAFE, which denotes, that unprivileged mounting of
this filesystem may not constitute a security problem.

Since most filesystems haven't been designed with unprivileged mounting in
mind, a thorough audit is needed before setting this flag.

For "safe" filesystems also allow unprivileged forced unmounting.

Move subtype handling from do_kern_mount() into do_new_mount().  All
other callers are kernel-internal and do not need subtype support.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-03 21:20:11.000000000 +0100
+++ linux/fs/namespace.c	2008-01-03 21:21:06.000000000 +0100
@@ -960,14 +960,16 @@ static bool is_mount_owner(struct vfsmou
 /*
  * umount is permitted for
  *  - sysadmin
- *  - mount owner, if not forced umount
+ *  - mount owner
+ *    o if not forced umount,
+ *    o if forced umount, and filesystem is "safe"
  */
 static bool permit_umount(struct vfsmount *mnt, int flags)
 {
 	if (capable(CAP_SYS_ADMIN))
 		return true;
 
-	if (flags & MNT_FORCE)
+	if ((flags & MNT_FORCE) && !(mnt->mnt_sb->s_type->fs_flags & FS_SAFE))
 		return false;
 
 	return is_mount_owner(mnt, current->fsuid);
@@ -1025,13 +1027,17 @@ asmlinkage long sys_oldumount(char __use
  * - mountpoint is not a symlink
  * - mountpoint is in a mount owned by the user
  */
-static bool permit_mount(struct nameidata *nd, int *flags)
+static bool permit_mount(struct nameidata *nd, struct file_system_type *type,
+			 int *flags)
 {
 	struct inode *inode = nd->path.dentry->d_inode;
 
 	if (capable(CAP_SYS_ADMIN))
 		return true;
 
+	if (type && !(type->fs_flags & FS_SAFE))
+		return false;
+
 	if (S_ISLNK(inode->i_mode))
 		return false;
 
@@ -1285,7 +1291,7 @@ static int do_loopback(struct nameidata 
 	struct vfsmount *mnt = NULL;
 	int err;
 
-	if (!permit_mount(nd, &flags))
+	if (!permit_mount(nd, NULL, &flags))
 		return -EPERM;
 	if (!old_name || !*old_name)
 		return -EINVAL;
@@ -1466,30 +1472,76 @@ out:
 	return err;
 }
 
+static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
+{
+	int err;
+	const char *subtype = strchr(fstype, '.');
+	if (subtype) {
+		subtype++;
+		err = -EINVAL;
+		if (!subtype[0])
+			goto err;
+	} else
+		subtype = "";
+
+	mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
+	err = -ENOMEM;
+	if (!mnt->mnt_sb->s_subtype)
+		goto err;
+	return mnt;
+
+ err:
+	mntput(mnt);
+	return ERR_PTR(err);
+}
+
 /*
  * create a new mount for userspace and request it to be added into the
  * namespace's tree
  */
-static int do_new_mount(struct nameidata *nd, char *type, int flags,
+static int do_new_mount(struct nameidata *nd, char *fstype, int flags,
 			int mnt_flags, char *name, void *data)
 {
+	int err;
 	struct vfsmount *mnt;
+	struct file_system_type *type;
 
-	if (!type || !memchr(type, 0, PAGE_SIZE))
+	if (!fstype || !memchr(fstype, 0, PAGE_SIZE))
 		return -EINVAL;
 
-	/* we need capabilities... */
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
-
-	mnt = do_kern_mount(type, flags & ~MS_SETUSER, name, data);
-	if (IS_ERR(mnt))
+	type = get_fs_type(fstype);
+	if (!type)
+		return -ENODEV;
+
+	err = -EPERM;
+	if (!permit_mount(nd, type, &flags))
+		goto out_put_filesystem;
+
+	if (flags & MS_SETUSER) {
+		err = reserve_user_mount();
+		if (err)
+			goto out_put_filesystem;
+	}
+
+	mnt = vfs_kern_mount(type, flags & ~MS_SETUSER, name, data);
+	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
+	    !mnt->mnt_sb->s_subtype)
+		mnt = fs_set_subtype(mnt, fstype);
+	put_filesystem(type);
+	if (IS_ERR(mnt)) {
+		if (flags & MS_SETUSER)
+			dec_nr_user_mounts();
 		return PTR_ERR(mnt);
+	}
 
 	if (flags & MS_SETUSER)
-		set_mnt_user(mnt);
+		__set_mnt_user(mnt);
 
 	return do_add_mount(mnt, nd, mnt_flags, NULL);
+
+ out_put_filesystem:
+	put_filesystem(type);
+	return err;
 }
 
 /*
@@ -1520,7 +1572,7 @@ int do_add_mount(struct vfsmount *newmnt
 	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
 		goto unlock;
 
-	/* MNT_USER was set earlier */
+	/* some flags may have been set earlier */
 	newmnt->mnt_flags |= mnt_flags;
 	if ((err = graft_tree(newmnt, nd)))
 		goto unlock;
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h	2008-01-03 21:15:35.000000000 +0100
+++ linux/include/linux/fs.h	2008-01-03 21:21:06.000000000 +0100
@@ -96,6 +96,7 @@ extern int dir_notify_enable;
 #define FS_REQUIRES_DEV 1 
 #define FS_BINARY_MOUNTDATA 2
 #define FS_HAS_SUBTYPE 4
+#define FS_SAFE 8		/* Safe to mount by unprivileged users */
 #define FS_REVAL_DOT	16384	/* Check the paths ".", ".." for staleness */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move()
 					 * during rename() internally.
Index: linux/fs/super.c
===================================================================
--- linux.orig/fs/super.c	2008-01-02 21:42:10.000000000 +0100
+++ linux/fs/super.c	2008-01-03 21:21:06.000000000 +0100
@@ -906,29 +906,6 @@ out:
 
 EXPORT_SYMBOL_GPL(vfs_kern_mount);
 
-static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
-{
-	int err;
-	const char *subtype = strchr(fstype, '.');
-	if (subtype) {
-		subtype++;
-		err = -EINVAL;
-		if (!subtype[0])
-			goto err;
-	} else
-		subtype = "";
-
-	mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
-	err = -ENOMEM;
-	if (!mnt->mnt_sb->s_subtype)
-		goto err;
-	return mnt;
-
- err:
-	mntput(mnt);
-	return ERR_PTR(err);
-}
-
 struct vfsmount *
 do_kern_mount(const char *fstype, int flags, const char *name, void *data)
 {
@@ -937,9 +914,6 @@ do_kern_mount(const char *fstype, int fl
 	if (!type)
 		return ERR_PTR(-ENODEV);
 	mnt = vfs_kern_mount(type, flags, name, data);
-	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
-	    !mnt->mnt_sb->s_subtype)
-		mnt = fs_set_subtype(mnt, fstype);
 	put_filesystem(type);
 	return mnt;
 }

--

Re: [patch 6/9] unprivileged mounts: allow unprivileged mounts

[Karel Zak]

On Tue, Jan 08, 2008 at 12:35:08PM +0100, Miklos Szeredi wrote:
> Define a new fs flag FS_SAFE, which denotes, that unprivileged mounting of
> this filesystem may not constitute a security problem.
> 
> Since most filesystems haven't been designed with unprivileged mounting in
> mind, a thorough audit is needed before setting this flag.
> 
> For "safe" filesystems also allow unprivileged forced unmounting.

 What about to list "safe" filesystems anywhere in /proc/fs/ ? I think
 it's very important information for admins.

 Note, your patch for mount(8) is always trying to use unprivileged
 mount(2) for non-root users. It's overkill when unprivileged mounts are
 supported for bind mounts and fuse only. It would be nice to check
 if FS is "safe" before switch to unprivileged mode.

 The "safe" definition is also very subjective and it depends on your
 level of paranoia. There should be a way (e.g. /proc) how control and
 modify the list of "safe" filesystems. For example I have no problem
 to mark cifs as "safe" for my home server.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>

Re: [patch 6/9] unprivileged mounts: allow unprivileged mounts

[Miklos Szeredi]

> On Tue, Jan 08, 2008 at 12:35:08PM +0100, Miklos Szeredi wrote:
> > Define a new fs flag FS_SAFE, which denotes, that unprivileged mounting of
> > this filesystem may not constitute a security problem.
> > 
> > Since most filesystems haven't been designed with unprivileged mounting in
> > mind, a thorough audit is needed before setting this flag.
> > 
> > For "safe" filesystems also allow unprivileged forced unmounting.
> 
>  What about to list "safe" filesystems anywhere in /proc/fs/ ? I think
>  it's very important information for admins.

Makes sense.  I'll cook up something.

>  Note, your patch for mount(8) is always trying to use unprivileged
>  mount(2) for non-root users. It's overkill when unprivileged mounts are
>  supported for bind mounts and fuse only. It would be nice to check
>  if FS is "safe" before switch to unprivileged mode.

I think the little gain in performance is not worth the added
complexity.  Especially if the added complexity is in the privileged
part, and itself can be a source of security holes.

>  The "safe" definition is also very subjective and it depends on your
>  level of paranoia. There should be a way (e.g. /proc) how control and
>  modify the list of "safe" filesystems. For example I have no problem
>  to mark cifs as "safe" for my home server.

OK, also makes some sense.  Pavel's examples do point out that fuse
isn't as safe as I'd like it to be, so perhaps it would make sense to
default to just bind mounts being allowed, and having to explicity
enable unprivileged fuse mounts with a sysctl or whatever.

Miklos

Re: [patch 6/9] unprivileged mounts: allow unprivileged mounts

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Define a new fs flag FS_SAFE, which denotes, that unprivileged mounting of
> this filesystem may not constitute a security problem.
> 
> Since most filesystems haven't been designed with unprivileged mounting in
> mind, a thorough audit is needed before setting this flag.
> 
> For "safe" filesystems also allow unprivileged forced unmounting.
> 
> Move subtype handling from do_kern_mount() into do_new_mount().  All
> other callers are kernel-internal and do not need subtype support.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

This patch itself doesn't assign FS_SAFE to any filesystems, so
presuming that there is such a thing as an fs safe for users to
mount, and/or users sign their systems away through a sysctl,
this patch in itself appears right.

Acked-by: Serge Hallyn <serue@us.ibm.com>

> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-03 21:20:11.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-03 21:21:06.000000000 +0100
> @@ -960,14 +960,16 @@ static bool is_mount_owner(struct vfsmou
>  /*
>   * umount is permitted for
>   *  - sysadmin
> - *  - mount owner, if not forced umount
> + *  - mount owner
> + *    o if not forced umount,
> + *    o if forced umount, and filesystem is "safe"
>   */
>  static bool permit_umount(struct vfsmount *mnt, int flags)
>  {
>  	if (capable(CAP_SYS_ADMIN))
>  		return true;
> 
> -	if (flags & MNT_FORCE)
> +	if ((flags & MNT_FORCE) && !(mnt->mnt_sb->s_type->fs_flags & FS_SAFE))
>  		return false;
> 
>  	return is_mount_owner(mnt, current->fsuid);
> @@ -1025,13 +1027,17 @@ asmlinkage long sys_oldumount(char __use
>   * - mountpoint is not a symlink
>   * - mountpoint is in a mount owned by the user
>   */
> -static bool permit_mount(struct nameidata *nd, int *flags)
> +static bool permit_mount(struct nameidata *nd, struct file_system_type *type,
> +			 int *flags)
>  {
>  	struct inode *inode = nd->path.dentry->d_inode;
> 
>  	if (capable(CAP_SYS_ADMIN))
>  		return true;
> 
> +	if (type && !(type->fs_flags & FS_SAFE))
> +		return false;
> +
>  	if (S_ISLNK(inode->i_mode))
>  		return false;
> 
> @@ -1285,7 +1291,7 @@ static int do_loopback(struct nameidata 
>  	struct vfsmount *mnt = NULL;
>  	int err;
> 
> -	if (!permit_mount(nd, &flags))
> +	if (!permit_mount(nd, NULL, &flags))
>  		return -EPERM;
>  	if (!old_name || !*old_name)
>  		return -EINVAL;
> @@ -1466,30 +1472,76 @@ out:
>  	return err;
>  }
> 
> +static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
> +{
> +	int err;
> +	const char *subtype = strchr(fstype, '.');
> +	if (subtype) {
> +		subtype++;
> +		err = -EINVAL;
> +		if (!subtype[0])
> +			goto err;
> +	} else
> +		subtype = "";
> +
> +	mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
> +	err = -ENOMEM;
> +	if (!mnt->mnt_sb->s_subtype)
> +		goto err;
> +	return mnt;
> +
> + err:
> +	mntput(mnt);
> +	return ERR_PTR(err);
> +}
> +
>  /*
>   * create a new mount for userspace and request it to be added into the
>   * namespace's tree
>   */
> -static int do_new_mount(struct nameidata *nd, char *type, int flags,
> +static int do_new_mount(struct nameidata *nd, char *fstype, int flags,
>  			int mnt_flags, char *name, void *data)
>  {
> +	int err;
>  	struct vfsmount *mnt;
> +	struct file_system_type *type;
> 
> -	if (!type || !memchr(type, 0, PAGE_SIZE))
> +	if (!fstype || !memchr(fstype, 0, PAGE_SIZE))
>  		return -EINVAL;
> 
> -	/* we need capabilities... */
> -	if (!capable(CAP_SYS_ADMIN))
> -		return -EPERM;
> -
> -	mnt = do_kern_mount(type, flags & ~MS_SETUSER, name, data);
> -	if (IS_ERR(mnt))
> +	type = get_fs_type(fstype);
> +	if (!type)
> +		return -ENODEV;
> +
> +	err = -EPERM;
> +	if (!permit_mount(nd, type, &flags))
> +		goto out_put_filesystem;
> +
> +	if (flags & MS_SETUSER) {
> +		err = reserve_user_mount();
> +		if (err)
> +			goto out_put_filesystem;
> +	}
> +
> +	mnt = vfs_kern_mount(type, flags & ~MS_SETUSER, name, data);
> +	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
> +	    !mnt->mnt_sb->s_subtype)
> +		mnt = fs_set_subtype(mnt, fstype);
> +	put_filesystem(type);
> +	if (IS_ERR(mnt)) {
> +		if (flags & MS_SETUSER)
> +			dec_nr_user_mounts();
>  		return PTR_ERR(mnt);
> +	}
> 
>  	if (flags & MS_SETUSER)
> -		set_mnt_user(mnt);
> +		__set_mnt_user(mnt);
> 
>  	return do_add_mount(mnt, nd, mnt_flags, NULL);
> +
> + out_put_filesystem:
> +	put_filesystem(type);
> +	return err;
>  }
> 
>  /*
> @@ -1520,7 +1572,7 @@ int do_add_mount(struct vfsmount *newmnt
>  	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
>  		goto unlock;
> 
> -	/* MNT_USER was set earlier */
> +	/* some flags may have been set earlier */
>  	newmnt->mnt_flags |= mnt_flags;
>  	if ((err = graft_tree(newmnt, nd)))
>  		goto unlock;
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h	2008-01-03 21:15:35.000000000 +0100
> +++ linux/include/linux/fs.h	2008-01-03 21:21:06.000000000 +0100
> @@ -96,6 +96,7 @@ extern int dir_notify_enable;
>  #define FS_REQUIRES_DEV 1 
>  #define FS_BINARY_MOUNTDATA 2
>  #define FS_HAS_SUBTYPE 4
> +#define FS_SAFE 8		/* Safe to mount by unprivileged users */
>  #define FS_REVAL_DOT	16384	/* Check the paths ".", ".." for staleness */
>  #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move()
>  					 * during rename() internally.
> Index: linux/fs/super.c
> ===================================================================
> --- linux.orig/fs/super.c	2008-01-02 21:42:10.000000000 +0100
> +++ linux/fs/super.c	2008-01-03 21:21:06.000000000 +0100
> @@ -906,29 +906,6 @@ out:
> 
>  EXPORT_SYMBOL_GPL(vfs_kern_mount);
> 
> -static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
> -{
> -	int err;
> -	const char *subtype = strchr(fstype, '.');
> -	if (subtype) {
> -		subtype++;
> -		err = -EINVAL;
> -		if (!subtype[0])
> -			goto err;
> -	} else
> -		subtype = "";
> -
> -	mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
> -	err = -ENOMEM;
> -	if (!mnt->mnt_sb->s_subtype)
> -		goto err;
> -	return mnt;
> -
> - err:
> -	mntput(mnt);
> -	return ERR_PTR(err);
> -}
> -
>  struct vfsmount *
>  do_kern_mount(const char *fstype, int flags, const char *name, void *data)
>  {
> @@ -937,9 +914,6 @@ do_kern_mount(const char *fstype, int fl
>  	if (!type)
>  		return ERR_PTR(-ENODEV);
>  	mnt = vfs_kern_mount(type, flags, name, data);
> -	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
> -	    !mnt->mnt_sb->s_subtype)
> -		mnt = fs_set_subtype(mnt, fstype);
>  	put_filesystem(type);
>  	return mnt;
>  }
> 
> --

[patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-allow-unprivileged-fuse-mounts.patch --]
[-- Type: text/plain, Size: 2598 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Use FS_SAFE for "fuse" fs type, but not for "fuseblk".

FUSE was designed from the beginning to be safe for unprivileged users.  This
has also been verified in practice over many years.  In addition unprivileged
mounts require the parent mount to be owned by the user, which is more strict
than the current userspace policy.

This will enable future installations to remove the suid-root fusermount
utility.

Don't require the "user_id=" and "group_id=" options for unprivileged mounts,
but if they are present, verify them for sanity.

Disallow the "allow_other" option for unprivileged mounts.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/fuse/inode.c
===================================================================
--- linux.orig/fs/fuse/inode.c	2008-01-03 17:13:13.000000000 +0100
+++ linux/fs/fuse/inode.c	2008-01-03 21:28:01.000000000 +0100
@@ -357,6 +357,19 @@ static int parse_fuse_opt(char *opt, str
 	d->max_read = ~0;
 	d->blksize = 512;
 
+	/*
+	 * For unprivileged mounts use current uid/gid.  Still allow
+	 * "user_id" and "group_id" options for compatibility, but
+	 * only if they match these values.
+	 */
+	if (!capable(CAP_SYS_ADMIN)) {
+		d->user_id = current->uid;
+		d->user_id_present = 1;
+		d->group_id = current->gid;
+		d->group_id_present = 1;
+
+	}
+
 	while ((p = strsep(&opt, ",")) != NULL) {
 		int token;
 		int value;
@@ -385,6 +398,8 @@ static int parse_fuse_opt(char *opt, str
 		case OPT_USER_ID:
 			if (match_int(&args[0], &value))
 				return 0;
+			if (d->user_id_present && d->user_id != value)
+				return 0;
 			d->user_id = value;
 			d->user_id_present = 1;
 			break;
@@ -392,6 +407,8 @@ static int parse_fuse_opt(char *opt, str
 		case OPT_GROUP_ID:
 			if (match_int(&args[0], &value))
 				return 0;
+			if (d->group_id_present && d->group_id != value)
+				return 0;
 			d->group_id = value;
 			d->group_id_present = 1;
 			break;
@@ -596,6 +613,10 @@ static int fuse_fill_super(struct super_
 	if (!parse_fuse_opt((char *) data, &d, is_bdev))
 		return -EINVAL;
 
+	/* This is a privileged option */
+	if ((d.flags & FUSE_ALLOW_OTHER) && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
 	if (is_bdev) {
 #ifdef CONFIG_BLOCK
 		if (!sb_set_blocksize(sb, d.blksize))
@@ -696,9 +717,9 @@ static int fuse_get_sb(struct file_syste
 static struct file_system_type fuse_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "fuse",
-	.fs_flags	= FS_HAS_SUBTYPE,
 	.get_sb		= fuse_get_sb,
 	.kill_sb	= kill_anon_super,
+	.fs_flags	= FS_HAS_SUBTYPE | FS_SAFE,
 };
 
 #ifdef CONFIG_BLOCK

--

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Pavel Machek]

On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
> 
> FUSE was designed from the beginning to be safe for unprivileged users.  This
> has also been verified in practice over many years.  In addition unprivileged

Eh? So 'kill -9 no longer works' and 'suspend no longer works' is not
considered important enough to even mention?

'updatedb no longer works' is not a problem?

Are you ready to offer shell account for bugtraq people to see how
long it survives?
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

> On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
> > From: Miklos Szeredi <mszeredi@suse.cz>
> > 
> > Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
> > 
> > FUSE was designed from the beginning to be safe for unprivileged users.  This
> > has also been verified in practice over many years.  In addition unprivileged
> 
> Eh? So 'kill -9 no longer works' and 'suspend no longer works' is not
> considered important enough to even mention?

No.  Because in practice they don't seem to matter.  Also because
there's no way in which fuse could be done differently to address
these issues.

The 'kill -9' thing is basically due to VFS level locking not being
interruptible.  It could be changed, but I'm not sure it's worth it.

For the suspend issue, there are also no easy solutions.

> 'updatedb no longer works' is not a problem?

I haven't seen any problems with updatedb, and haven't had any bug
reports about it either.

> Are you ready to offer shell account for bugtraq people to see how
> long it survives?

Bugtraq people are free to install fuse on their machines and take it
apart.

AFAIR there were two security vulnerabilities in fuse's history, one
of them an information leak in the kernel module, and the other one an
mtab corruption issue in the fusermount utility.  I don't think this
is such a bad track record.

Miklos

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Pavel Machek]

On Tue 2008-01-08 23:42:20, Miklos Szeredi wrote:
> > On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
> > > From: Miklos Szeredi <mszeredi@suse.cz>
> > > 
> > > Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
> > > 
> > > FUSE was designed from the beginning to be safe for unprivileged users.  This
> > > has also been verified in practice over many years.  In addition unprivileged
> > 
> > Eh? So 'kill -9 no longer works' and 'suspend no longer works' is not
> > considered important enough to even mention?
> 
> No.  Because in practice they don't seem to matter.  Also because
> there's no way in which fuse could be done differently to address
> these issues.
> 
> The 'kill -9' thing is basically due to VFS level locking not being
> interruptible.  It could be changed, but I'm not sure it's worth it.

Well, I believe it should be changed. "You need to mount /sys, then
echo X to Y before kill -9 works" does not look nice... I agree it is
not easy.

> > 'updatedb no longer works' is not a problem?
> 
> I haven't seen any problems with updatedb, and haven't had any bug
> reports about it either.

Ok, I don't know much about FUSE. In current version, if user creates
infinite maze and mounts it under ~, updatedb just does not enter it?

> AFAIR there were two security vulnerabilities in fuse's history, one
> of them an information leak in the kernel module, and the other one an
> mtab corruption issue in the fusermount utility.  I don't think this
> is such a bad track record.

Not bad indeed. But I'd consider 'kill -9 not working' to be DoS
vulnerability... and I'm woried about problems fuse + user mounts
expose in other parts of system.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

> > > 'updatedb no longer works' is not a problem?
> > 
> > I haven't seen any problems with updatedb, and haven't had any bug
> > reports about it either.
> 
> Ok, I don't know much about FUSE. In current version, if user creates
> infinite maze and mounts it under ~, updatedb just does not enter it?

It doesn't.  See Documentation/filesystems/fuse.txt

> > AFAIR there were two security vulnerabilities in fuse's history, one
> > of them an information leak in the kernel module, and the other one an
> > mtab corruption issue in the fusermount utility.  I don't think this
> > is such a bad track record.
> 
> Not bad indeed. But I'd consider 'kill -9 not working' to be DoS
> vulnerability...

The worst that can happen is that a sysadmin doesn't read the docs
(likely) before enabling fuse on a multiuser system, and is surprised
by a user doing funny things.  And _then_ has to go read the docs, or
google for some info.  This is basically how things normally work, and
I don't consider it a DoS.

> and I'm woried about problems fuse + user mounts expose in other
> parts of system.

I'm worried too, and I'm not saying that enabling unprivileged fuse
mounts is completely risk free.  Nothing is, and nobody is forced to
do it.

Miklos

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Pavel Machek]

Hi!

> > > AFAIR there were two security vulnerabilities in fuse's history, one
> > > of them an information leak in the kernel module, and the other one an
> > > mtab corruption issue in the fusermount utility.  I don't think this
> > > is such a bad track record.
> > 
> > Not bad indeed. But I'd consider 'kill -9 not working' to be DoS
> > vulnerability...
> 
> The worst that can happen is that a sysadmin doesn't read the docs
> (likely) before enabling fuse on a multiuser system, and is surprised
> by a user doing funny things.  And _then_ has to go read the docs, or
> google for some info.  This is basically how things normally work, and
> I don't consider it a DoS.

No, this is not normal. Kill -9 has been estabilished long time ago,
and we should not be documenting its now-brokenness in
Documentation/filesystems/fuse.txt .

For example, my /etc/inittab currently has:

kb::kbrequest:/etc/rc/rc.reboot 2 0

#
# This file handles system shutdown and reboot.
#

PATH=/sbin:/bin:/usr/sbin:/usr/bin
sync &

# Kill all processes.
wall System is going down NOW\!
echo -n -e "\rSystem is going down: processes."
killall5 -15
echo -n "."
sleep 1
echo -n ". "
killall5 -9

# Before unmounting file systems write a reboot record to wtmp.
echo -n "wtmp "
halt -w

# Swap needs to be unmounted because otherwise busy filesystems
remain.
echo -n "swap "
swapoff -a
swapoff /c/swap
swapoff /c/swap2

# Unmount file systems
echo -n "umount."
umount -a || (
	sync &
	echo -n "umount-retry."
	sleep 1
	umount -a || sulogin
)
echo -n ". "
mount -n -o remount,ro /

# Now halt or reboot.
if [ "$2" = "0" ] ; then
	swapoff -a
	echo "halted."
	halt -p -f
else
	echo "rebooting..."
	reboot -d -f
fi

...this will break with FUSE enabled, right? (Minor security hole by
allowing users to stop c-a-delete, where none existed before?)

I'm currently suspending by 'echo "mem" > /sys/power/state'. How
should I do that _safely_ with FUSE enabled?

If I want to get rid of nasty user in multiuser system, I do 
su nastyuser 'kill -9 -1' . How do I do the equivalent with FUSE
enabled? (Without affecting other users?)

Load average was never really meaningful number, but with FUSE
enabled, users can set it to 666 without actually eating any CPU.

SIGSTOP used to work, allowing you to prevent user processes from
working while you examine them. Now SIGSTOP can be delayed for
arbitrary time.

Heck, imagine malicious user process misbehaves. Before FUSE, you
could at least attach it with gdb to look what it is doing. Now you
can't.

I really believe FUSE vs. signals needs fixing. Either that, or
updating all the manpages

man 1 kill:
-       KILL       9   exit      this signal may not be blocked
+       KILL       9   exit      this signal may not be blocked, except by FUSE user mount

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

> ...this will break with FUSE enabled, right? (Minor security hole by
> allowing users to stop c-a-delete, where none existed before?)

Yup (or I don't know, I'm sure there was or is some problem with
ptrace, that could be used to create unkillable processes).

Fuse could actually be fixed to exit reliably for 'killall5 -9' (it
used to), but that has other problems, and it doesn't seem very
important to me.  But this can be discussed.

What cannot be fixed is if one process is inside an fs operation
(e.g. unlink), holding a VFS lock (i_mutex) and another process goes
to uninterruptible sleep on that lock.  There's no way (other than
rewriting the VFS) in which that second process could be killed unless
you kill the first one or the fuse server.

> I'm currently suspending by 'echo "mem" > /sys/power/state'. How
> should I do that _safely_ with FUSE enabled?

You can't.  But that's only solvable with

 - rewrite of VFS (see above)
 - rewrite of freezer

> If I want to get rid of nasty user in multiuser system, I do 
> su nastyuser 'kill -9 -1' . How do I do the equivalent with FUSE
> enabled? (Without affecting other users?)

You can still do that.  If a process cannot be killed with 'kill -9',
due to being deadlocked with itself through fuse (not an easy feat to
accomplish), then it's not going to do any more harm, and you _can_
get rid of it by forced umounting the filesystem, or if it has been
detached, through the fusectl filesystem.

> Load average was never really meaningful number, but with FUSE
> enabled, users can set it to 666 without actually eating any CPU.
> 
> SIGSTOP used to work, allowing you to prevent user processes from
> working while you examine them. Now SIGSTOP can be delayed for
> arbitrary time.

Making filesystem operations restartable is not easy.  I would say
near impossible, but I haven't given a lot of enery into investigating.

> Heck, imagine malicious user process misbehaves. Before FUSE, you
> could at least attach it with gdb to look what it is doing. Now you
> can't.

Sure, but you can check in other ways (/proc/$PID/wchan), sysrq-t.

> I really believe FUSE vs. signals needs fixing. Either that, or
> updating all the manpages
> 
> man 1 kill:
> -       KILL       9   exit      this signal may not be blocked
> +       KILL       9   exit      this signal may not be blocked, except by FUSE user mount

Heh, there are all very interesting, but most of these issues are not
even on my todo list (which has grown into quite a big pile over the
years), which means, that they don't seem to matter to people in
practice.

You seem to be implying that fuse is worthless if these issues are not
fixed, but that is very far from the truth, I think.

Miklos

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Pavel Machek]

Hi!

> > ...this will break with FUSE enabled, right? (Minor security hole by
> > allowing users to stop c-a-delete, where none existed before?)
> 
> Yup (or I don't know, I'm sure there was or is some problem with
> ptrace, that could be used to create unkillable processes).
> 
> Fuse could actually be fixed to exit reliably for 'killall5 -9' (it
> used to), but that has other problems, and it doesn't seem very
> important to me.  But this can be discussed.

I think it is better to fix fuse than to rewrite all the shutdown scripts.

> What cannot be fixed is if one process is inside an fs operation
> (e.g. unlink), holding a VFS lock (i_mutex) and another process goes
> to uninterruptible sleep on that lock.  There's no way (other than
> rewriting the VFS) in which that second process could be killed unless
> you kill the first one or the fuse server.

I believe VFS should be rewritten here. Perhaps new "TASK_KILLABLE"
state can help?

> > I really believe FUSE vs. signals needs fixing. Either that, or
> > updating all the manpages
> > 
> > man 1 kill:
> > -       KILL       9   exit      this signal may not be blocked
> > +       KILL       9   exit      this signal may not be blocked, except by FUSE user mount
> 
> Heh, there are all very interesting, but most of these issues are not
> even on my todo list (which has grown into quite a big pile over the
> years), which means, that they don't seem to matter to people in
> practice.
> 
> You seem to be implying that fuse is worthless if these issues are not
> fixed, but that is very far from the truth, I think.

I'm not saying fuse is worthless. It is a nice toy for single-user
systems. But I do not think we should be merging "allow ordinary users
to mount their own fuse's" before issues above are fixed.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

> I'm not saying fuse is worthless. It is a nice toy for single-user
> systems. But I do not think we should be merging "allow ordinary users
> to mount their own fuse's" before issues above are fixed.

I think multi user systems are not all that interesting.  And I
suspect very few of them want reliably working suspend/hibernate
(which they wouldn't get due to other issues anyway), or have weird
shutdown scripts which stop when they are unable to umount
filesystems.

For paranoid sysadmins, I suggest not enabling fuse for unprivileged
users, which is pretty easy to do: just don't set /dev/fuse to be
world read-writable (which is the default BTW).

So your reasons just don't warrant a big effort involving VFS hacking,
etc.  Patches are of course welcome.

Miklos

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Pavel Machek]

On Wed 2008-01-09 14:48:53, Miklos Szeredi wrote:
> > I'm not saying fuse is worthless. It is a nice toy for single-user
> > systems. But I do not think we should be merging "allow ordinary users
> > to mount their own fuse's" before issues above are fixed.
> 
> I think multi user systems are not all that interesting.  And I
> suspect very few of them want reliably working suspend/hibernate
> (which they wouldn't get due to other issues anyway), or have weird
> shutdown scripts which stop when they are unable to umount
> filesystems.

Weird shutdown scripts? I believe all shutdown scripts have this issue
-- if you want to [cleanly] unmount your / filesystem, you need all
the opens for write closed, right...? Which self-deadlocked fused
holding files open will prevent.

> For paranoid sysadmins, I suggest not enabling fuse for unprivileged
> users, which is pretty easy to do: just don't set /dev/fuse to be
> world read-writable (which is the default BTW).
> 
> So your reasons just don't warrant a big effort involving VFS hacking,
> etc.  Patches are of course welcome.

Well, I believe code with obscure, but almost impossible to fix
problems should not be merged... because that means it will not be
fixed and we'll just have to live with broken kill -9 forever.

Anyway, I believe it would be fair to mention kill -9 no longer
working and shutdown/hibernation/multiuser problems it implies in the
changelogs and probably sysctl documentation or how is this enabled.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

> > > I'm not saying fuse is worthless. It is a nice toy for single-user
> > > systems. But I do not think we should be merging "allow ordinary users
> > > to mount their own fuse's" before issues above are fixed.
> > 
> > I think multi user systems are not all that interesting.  And I
> > suspect very few of them want reliably working suspend/hibernate
> > (which they wouldn't get due to other issues anyway), or have weird
> > shutdown scripts which stop when they are unable to umount
> > filesystems.
> 
> Weird shutdown scripts? I believe all shutdown scripts have this issue
> -- if you want to [cleanly] unmount your / filesystem, you need all
> the opens for write closed, right...? Which self-deadlocked fused
> holding files open will prevent.
> 
> > For paranoid sysadmins, I suggest not enabling fuse for unprivileged
> > users, which is pretty easy to do: just don't set /dev/fuse to be
> > world read-writable (which is the default BTW).
> > 
> > So your reasons just don't warrant a big effort involving VFS hacking,
> > etc.  Patches are of course welcome.
> 
> Well, I believe code with obscure, but almost impossible to fix
> problems should not be merged...

That code _has_ been merged, something like 3 years ago, and is doing
fine, thank you.

The unprivileged mounts code, which we should be discussing, doesn't
change anything about that, except to not require another suid-root
utility.  Many distributions enabling unprivileged mounting by default
_now_, so it's not as if there's some great danger in doing this
slightly differently.

> Anyway, I believe it would be fair to mention kill -9 no longer
> working and shutdown/hibernation/multiuser problems it implies in the
> changelogs and probably sysctl documentation or how is this enabled.

Sure.

Miklos

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Nigel Cunningham]

Hi.

Miklos Szeredi wrote:
>> On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
>>> From: Miklos Szeredi <mszeredi@suse.cz>
>>>
>>> Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
>>>
>>> FUSE was designed from the beginning to be safe for unprivileged users.  This
>>> has also been verified in practice over many years.  In addition unprivileged
>> Eh? So 'kill -9 no longer works' and 'suspend no longer works' is not
>> considered important enough to even mention?
> 
> No.  Because in practice they don't seem to matter.  Also because
> there's no way in which fuse could be done differently to address
> these issues.

Could you clarify, please? I hope I'm getting the wrong end of the stick
- it sounds to me like you and Pavel are saying that this patch breaks
suspending to ram (and hibernating?) but you want to push it anyway
because you haven't been able to produce an instance, don't think
suspending or hibernating matter and couldn't fix fuse anyway?

> The 'kill -9' thing is basically due to VFS level locking not being
> interruptible.  It could be changed, but I'm not sure it's worth it.
> 
> For the suspend issue, there are also no easy solutions.

What are the non-easy solutions?

Regards,

Nigel

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

> >> On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
> >>> From: Miklos Szeredi <mszeredi@suse.cz>
> >>>
> >>> Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
> >>>
> >>> FUSE was designed from the beginning to be safe for unprivileged users.  This
> >>> has also been verified in practice over many years.  In addition unprivileged
> >> Eh? So 'kill -9 no longer works' and 'suspend no longer works' is not
> >> considered important enough to even mention?
> > 
> > No.  Because in practice they don't seem to matter.  Also because
> > there's no way in which fuse could be done differently to address
> > these issues.
> 
> Could you clarify, please? I hope I'm getting the wrong end of the stick
> - it sounds to me like you and Pavel are saying that this patch breaks
> suspending to ram (and hibernating?) but you want to push it anyway
> because you haven't been able to produce an instance, don't think
> suspending or hibernating matter and couldn't fix fuse anyway?

This patch has nothing to do with suspend or hibernate.  What this
patchset does, is help get rid of fusermount, a suid-root mount
helper.  It also opens up new possibilities, which are not fuse
related.

Fuse has bad interactions with the freezer, theoretically.  In
practice, I remember just one bug report (that sparked off this whole
"do we need freezer, or don't we" flamefest), that actually got fixed
fairly quickly, ...maybe.  Rafael probably remembers better.

> > The 'kill -9' thing is basically due to VFS level locking not being
> > interruptible.  It could be changed, but I'm not sure it's worth it.
> > 
> > For the suspend issue, there are also no easy solutions.
> 
> What are the non-easy solutions?

The ability to freeze tasks in uninterruptible sleep, or more
generally at any preempt point (except when drivers are poking
hardware).

I know this doesn't play well with userspace hibernate, and I don't
think it can be resolved without going the kexec way.

Miklos

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Nigel Cunningham]

Hi.

Miklos Szeredi wrote:
>>>> On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
>>>>> From: Miklos Szeredi <mszeredi@suse.cz>
>>>>>
>>>>> Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
>>>>>
>>>>> FUSE was designed from the beginning to be safe for unprivileged users.  This
>>>>> has also been verified in practice over many years.  In addition unprivileged
>>>> Eh? So 'kill -9 no longer works' and 'suspend no longer works' is not
>>>> considered important enough to even mention?
>>> No.  Because in practice they don't seem to matter.  Also because
>>> there's no way in which fuse could be done differently to address
>>> these issues.
>> Could you clarify, please? I hope I'm getting the wrong end of the stick
>> - it sounds to me like you and Pavel are saying that this patch breaks
>> suspending to ram (and hibernating?) but you want to push it anyway
>> because you haven't been able to produce an instance, don't think
>> suspending or hibernating matter and couldn't fix fuse anyway?
> 
> This patch has nothing to do with suspend or hibernate.  What this
> patchset does, is help get rid of fusermount, a suid-root mount
> helper.  It also opens up new possibilities, which are not fuse
> related.

That's what I thought. So what was Pavel talking about with "kill -9 no
longer works" and "suspend no longer works" above? I couldn't understand
it from the context.

> Fuse has bad interactions with the freezer, theoretically.  In
> practice, I remember just one bug report (that sparked off this whole
> "do we need freezer, or don't we" flamefest), that actually got fixed
> fairly quickly, ...maybe.  Rafael probably remembers better.

I think they just gave up and considered it unsolvable. I'm not sure it is.

>>> The 'kill -9' thing is basically due to VFS level locking not being
>>> interruptible.  It could be changed, but I'm not sure it's worth it.
>>>
>>> For the suspend issue, there are also no easy solutions.
>> What are the non-easy solutions?
> 
> The ability to freeze tasks in uninterruptible sleep, or more
> generally at any preempt point (except when drivers are poking
> hardware).

Couldn't some sort of scheduler based solution deal with the
uninterruptible sleeping case?

> I know this doesn't play well with userspace hibernate, and I don't
> think it can be resolved without going the kexec way.

I can see the desirability of kexec when it comes to avoiding the
freezer, but comes with its own problems too - having the original
context usable is handy, not having to set aside a large amount of space
for a second kernel is also desirable and there are still greater issues
of transferring information backwards and forwards between the two kernels.

Regards,

Nigel

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Pavel Machek]

On Wed 2008-01-09 09:47:31, Miklos Szeredi wrote:
> > >> On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
> > >>> From: Miklos Szeredi <mszeredi@suse.cz>
> > >>>
> > >>> Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
> > >>>
> > >>> FUSE was designed from the beginning to be safe for unprivileged users.  This
> > >>> has also been verified in practice over many years.  In addition unprivileged
> > >> Eh? So 'kill -9 no longer works' and 'suspend no longer works' is not
> > >> considered important enough to even mention?
> > > 
> > > No.  Because in practice they don't seem to matter.  Also because
> > > there's no way in which fuse could be done differently to address
> > > these issues.
> > 
> > Could you clarify, please? I hope I'm getting the wrong end of the stick
> > - it sounds to me like you and Pavel are saying that this patch breaks
> > suspending to ram (and hibernating?) but you want to push it anyway
> > because you haven't been able to produce an instance, don't think
> > suspending or hibernating matter and couldn't fix fuse anyway?
> 
> This patch has nothing to do with suspend or hibernate.  What this
> patchset does, is help get rid of fusermount, a suid-root mount
> helper.  It also opens up new possibilities, which are not fuse
> related.
> 
> Fuse has bad interactions with the freezer, theoretically.  In
> practice, I remember just one bug report (that sparked off this whole
> "do we need freezer, or don't we" flamefest), that actually got fixed
> fairly quickly, ...maybe.  Rafael probably remembers better.

In practice, if the "unpriviledged fuse" gets enabled, any user can
prevent suspend/hibernation from working.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Szabolcs Szakacsits]

Hi,

On Wed, 9 Jan 2008, Nigel Cunningham wrote:
> On Tue 2008-01-08 12:35:09, Miklos Szeredi wrote:
> >
> > For the suspend issue, there are also no easy solutions.
> 
> What are the non-easy solutions?

A practical point of view I've seen only fuse rootfs mounts to be a 
problem. I remember Ubuntu patches for this (WUBI and some other distros 
install NTFS root). But this probably also depends on the used suspend 
implementation.

Personally I've never had fuse related suspend problem with ordinary mounts 
during heavy use under development, nor NTFS user problem was tracked down 
to it in the last one and half year.

Regards,
	    Szaka

-- 
NTFS-3G:  http://ntfs-3g.org

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Use FS_SAFE for "fuse" fs type, but not for "fuseblk".
> 
> FUSE was designed from the beginning to be safe for unprivileged users.  This
> has also been verified in practice over many years.  In addition unprivileged
> mounts require the parent mount to be owned by the user, which is more strict
> than the current userspace policy.
> 
> This will enable future installations to remove the suid-root fusermount
> utility.
> 
> Don't require the "user_id=" and "group_id=" options for unprivileged mounts,
> but if they are present, verify them for sanity.
> 
> Disallow the "allow_other" option for unprivileged mounts.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Sounds like a sysctl to enable FS_SAFE for fuse will make this patch
acceptable to everyone?

> ---
> 
> Index: linux/fs/fuse/inode.c
> ===================================================================
> --- linux.orig/fs/fuse/inode.c	2008-01-03 17:13:13.000000000 +0100
> +++ linux/fs/fuse/inode.c	2008-01-03 21:28:01.000000000 +0100
> @@ -357,6 +357,19 @@ static int parse_fuse_opt(char *opt, str
>  	d->max_read = ~0;
>  	d->blksize = 512;
> 
> +	/*
> +	 * For unprivileged mounts use current uid/gid.  Still allow
> +	 * "user_id" and "group_id" options for compatibility, but
> +	 * only if they match these values.
> +	 */
> +	if (!capable(CAP_SYS_ADMIN)) {
> +		d->user_id = current->uid;
> +		d->user_id_present = 1;
> +		d->group_id = current->gid;
> +		d->group_id_present = 1;
> +
> +	}
> +
>  	while ((p = strsep(&opt, ",")) != NULL) {
>  		int token;
>  		int value;
> @@ -385,6 +398,8 @@ static int parse_fuse_opt(char *opt, str
>  		case OPT_USER_ID:
>  			if (match_int(&args[0], &value))
>  				return 0;
> +			if (d->user_id_present && d->user_id != value)
> +				return 0;
>  			d->user_id = value;
>  			d->user_id_present = 1;
>  			break;
> @@ -392,6 +407,8 @@ static int parse_fuse_opt(char *opt, str
>  		case OPT_GROUP_ID:
>  			if (match_int(&args[0], &value))
>  				return 0;
> +			if (d->group_id_present && d->group_id != value)
> +				return 0;
>  			d->group_id = value;
>  			d->group_id_present = 1;
>  			break;
> @@ -596,6 +613,10 @@ static int fuse_fill_super(struct super_
>  	if (!parse_fuse_opt((char *) data, &d, is_bdev))
>  		return -EINVAL;
> 
> +	/* This is a privileged option */
> +	if ((d.flags & FUSE_ALLOW_OTHER) && !capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
>  	if (is_bdev) {
>  #ifdef CONFIG_BLOCK
>  		if (!sb_set_blocksize(sb, d.blksize))
> @@ -696,9 +717,9 @@ static int fuse_get_sb(struct file_syste
>  static struct file_system_type fuse_fs_type = {
>  	.owner		= THIS_MODULE,
>  	.name		= "fuse",
> -	.fs_flags	= FS_HAS_SUBTYPE,
>  	.get_sb		= fuse_get_sb,
>  	.kill_sb	= kill_anon_super,
> +	.fs_flags	= FS_HAS_SUBTYPE | FS_SAFE,
>  };
> 
>  #ifdef CONFIG_BLOCK
> 
> --

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

> Sounds like a sysctl to enable FS_SAFE for fuse will make this patch
> acceptable to everyone?

I think the most generic approach, is to be able to set "safeness" for
any fs type, not just fuse (Karel's suggestion).

E.g:

  echo 1 > /proc/sys/fs/types/cifs/safe

This would also provide a way to query the FS_SAFE flag.

Miklos

Re: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> > Sounds like a sysctl to enable FS_SAFE for fuse will make this patch
> > acceptable to everyone?
> 
> I think the most generic approach, is to be able to set "safeness" for
> any fs type, not just fuse (Karel's suggestion).
> 
> E.g:
> 
>   echo 1 > /proc/sys/fs/types/cifs/safe
> 
> This would also provide a way to query the FS_SAFE flag.

That sounds good.

-serge

[patch 8/9] unprivileged mounts: propagation: inherit owner from parent

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-propagation-inherit-owner-from-parent.patch --]
[-- Type: text/plain, Size: 7062 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

On mount propagation, let the owner of the clone be inherited from the
parent into which it has been propagated.  Also if the parent has the
"nosuid" flag, set this flag for the child as well.

This makes sense for example, when propagation is set up from the
initial namespace into a per-user namespace, where some or all of the
mounts may be owned by the user.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-04 13:48:14.000000000 +0100
+++ linux/fs/namespace.c	2008-01-04 13:49:52.000000000 +0100
@@ -500,10 +500,10 @@ static int reserve_user_mount(void)
 	return err;
 }
 
-static void __set_mnt_user(struct vfsmount *mnt)
+static void __set_mnt_user(struct vfsmount *mnt, uid_t owner)
 {
 	BUG_ON(mnt->mnt_flags & MNT_USER);
-	mnt->mnt_uid = current->fsuid;
+	mnt->mnt_uid = owner;
 	mnt->mnt_flags |= MNT_USER;
 
 	if (!capable(CAP_SETUID))
@@ -514,7 +514,7 @@ static void __set_mnt_user(struct vfsmou
 
 static void set_mnt_user(struct vfsmount *mnt)
 {
-	__set_mnt_user(mnt);
+	__set_mnt_user(mnt, current->fsuid);
 	spin_lock(&vfsmount_lock);
 	nr_user_mounts++;
 	spin_unlock(&vfsmount_lock);
@@ -530,7 +530,7 @@ static void clear_mnt_user(struct vfsmou
 }
 
 static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
-					int flag)
+					int flag, uid_t owner)
 {
 	struct super_block *sb = old->mnt_sb;
 	struct vfsmount *mnt;
@@ -554,7 +554,10 @@ static struct vfsmount *clone_mnt(struct
 	/* don't copy the MNT_USER flag */
 	mnt->mnt_flags &= ~MNT_USER;
 	if (flag & CL_SETUSER)
-		__set_mnt_user(mnt);
+		__set_mnt_user(mnt, owner);
+
+	if (flag & CL_NOSUID)
+		mnt->mnt_flags |= MNT_NOSUID;
 
 	if (flag & CL_SLAVE) {
 		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
@@ -1060,7 +1063,7 @@ static int lives_below_in_same_fs(struct
 }
 
 struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
-					int flag)
+					int flag, uid_t owner)
 {
 	struct vfsmount *res, *p, *q, *r, *s;
 	struct nameidata nd;
@@ -1068,7 +1071,7 @@ struct vfsmount *copy_tree(struct vfsmou
 	if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
 		return ERR_PTR(-EPERM);
 
-	res = q = clone_mnt(mnt, dentry, flag);
+	res = q = clone_mnt(mnt, dentry, flag, owner);
 	if (IS_ERR(q))
 		goto error;
 	q->mnt_mountpoint = mnt->mnt_mountpoint;
@@ -1090,7 +1093,7 @@ struct vfsmount *copy_tree(struct vfsmou
 			p = s;
 			nd.path.mnt = q;
 			nd.path.dentry = p->mnt_mountpoint;
-			q = clone_mnt(p, p->mnt_root, flag);
+			q = clone_mnt(p, p->mnt_root, flag, owner);
 			if (IS_ERR(q))
 				goto error;
 			spin_lock(&vfsmount_lock);
@@ -1115,7 +1118,7 @@ struct vfsmount *collect_mounts(struct v
 {
 	struct vfsmount *tree;
 	down_read(&namespace_sem);
-	tree = copy_tree(mnt, dentry, CL_COPY_ALL | CL_PRIVATE);
+	tree = copy_tree(mnt, dentry, CL_COPY_ALL | CL_PRIVATE, 0);
 	up_read(&namespace_sem);
 	return tree;
 }
@@ -1286,7 +1289,8 @@ static int do_change_type(struct nameida
  */
 static int do_loopback(struct nameidata *nd, char *old_name, int flags)
 {
-	int clone_fl;
+	int clone_fl = 0;
+	uid_t owner = 0;
 	struct nameidata old_nd;
 	struct vfsmount *mnt = NULL;
 	int err;
@@ -1307,11 +1311,17 @@ static int do_loopback(struct nameidata 
 	if (!check_mnt(nd->path.mnt) || !check_mnt(old_nd.path.mnt))
 		goto out;
 
-	clone_fl = (flags & MS_SETUSER) ? CL_SETUSER : 0;
+	if (flags & MS_SETUSER) {
+		clone_fl |= CL_SETUSER;
+		owner = current->fsuid;
+	}
+
 	if (flags & MS_REC)
-		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
+		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl,
+				owner);
 	else
-		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
+		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl,
+				owner);
 
 	err = PTR_ERR(mnt);
 	if (IS_ERR(mnt))
@@ -1535,7 +1545,7 @@ static int do_new_mount(struct nameidata
 	}
 
 	if (flags & MS_SETUSER)
-		__set_mnt_user(mnt);
+		__set_mnt_user(mnt, current->fsuid);
 
 	return do_add_mount(mnt, nd, mnt_flags, NULL);
 
@@ -1931,7 +1941,7 @@ static struct mnt_namespace *dup_mnt_ns(
 	down_write(&namespace_sem);
 	/* First pass: copy the tree topology */
 	new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
-					CL_COPY_ALL | CL_EXPIRE);
+					CL_COPY_ALL | CL_EXPIRE, 0);
 	if (IS_ERR(new_ns->root)) {
 		up_write(&namespace_sem);
 		kfree(new_ns);
Index: linux/fs/pnode.c
===================================================================
--- linux.orig/fs/pnode.c	2008-01-04 13:47:49.000000000 +0100
+++ linux/fs/pnode.c	2008-01-04 13:49:12.000000000 +0100
@@ -181,15 +181,28 @@ int propagate_mnt(struct vfsmount *dest_
 
 	for (m = propagation_next(dest_mnt, dest_mnt); m;
 			m = propagation_next(m, dest_mnt)) {
-		int type;
+		int clflags;
+		uid_t owner = 0;
 		struct vfsmount *source;
 
 		if (IS_MNT_NEW(m))
 			continue;
 
-		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
+		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &clflags);
 
-		child = copy_tree(source, source->mnt_root, type);
+		if (m->mnt_flags & MNT_USER) {
+			clflags |= CL_SETUSER;
+			owner = m->mnt_uid;
+
+			/*
+			 * If propagating into a user mount which doesn't
+			 * allow suid, then make sure, the child(ren) won't
+			 * allow suid either
+			 */
+			if (m->mnt_flags & MNT_NOSUID)
+				clflags |= CL_NOSUID;
+		}
+		child = copy_tree(source, source->mnt_root, clflags, owner);
 		if (IS_ERR(child)) {
 			ret = PTR_ERR(child);
 			list_splice(tree_list, tmp_list.prev);
Index: linux/fs/pnode.h
===================================================================
--- linux.orig/fs/pnode.h	2008-01-04 13:45:45.000000000 +0100
+++ linux/fs/pnode.h	2008-01-04 13:49:12.000000000 +0100
@@ -24,6 +24,7 @@
 #define CL_PROPAGATION 		0x10
 #define CL_PRIVATE 		0x20
 #define CL_SETUSER		0x40
+#define CL_NOSUID		0x80
 
 static inline void set_mnt_shared(struct vfsmount *mnt)
 {
@@ -36,4 +37,6 @@ int propagate_mnt(struct vfsmount *, str
 		struct list_head *);
 int propagate_umount(struct list_head *);
 int propagate_mount_busy(struct vfsmount *, int);
+struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int, uid_t);
+
 #endif /* _LINUX_PNODE_H */
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h	2008-01-04 13:48:14.000000000 +0100
+++ linux/include/linux/fs.h	2008-01-04 13:49:12.000000000 +0100
@@ -1492,7 +1492,6 @@ extern int may_umount(struct vfsmount *)
 extern void umount_tree(struct vfsmount *, int, struct list_head *);
 extern void release_mounts(struct list_head *);
 extern long do_mount(char *, char *, char *, unsigned long, void *);
-extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
 extern void mnt_set_mountpoint(struct vfsmount *, struct dentry *,
 				  struct vfsmount *);
 extern struct vfsmount *collect_mounts(struct vfsmount *, struct dentry *);

--

Re: [patch 8/9] unprivileged mounts: propagation: inherit owner from parent

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> On mount propagation, let the owner of the clone be inherited from the
> parent into which it has been propagated.  Also if the parent has the
> "nosuid" flag, set this flag for the child as well.

What about nodev?

thanks,
-serge

> 
> This makes sense for example, when propagation is set up from the
> initial namespace into a per-user namespace, where some or all of the
> mounts may be owned by the user.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-04 13:48:14.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-04 13:49:52.000000000 +0100
> @@ -500,10 +500,10 @@ static int reserve_user_mount(void)
>  	return err;
>  }
> 
> -static void __set_mnt_user(struct vfsmount *mnt)
> +static void __set_mnt_user(struct vfsmount *mnt, uid_t owner)
>  {
>  	BUG_ON(mnt->mnt_flags & MNT_USER);
> -	mnt->mnt_uid = current->fsuid;
> +	mnt->mnt_uid = owner;
>  	mnt->mnt_flags |= MNT_USER;
> 
>  	if (!capable(CAP_SETUID))
> @@ -514,7 +514,7 @@ static void __set_mnt_user(struct vfsmou
> 
>  static void set_mnt_user(struct vfsmount *mnt)
>  {
> -	__set_mnt_user(mnt);
> +	__set_mnt_user(mnt, current->fsuid);
>  	spin_lock(&vfsmount_lock);
>  	nr_user_mounts++;
>  	spin_unlock(&vfsmount_lock);
> @@ -530,7 +530,7 @@ static void clear_mnt_user(struct vfsmou
>  }
> 
>  static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
> -					int flag)
> +					int flag, uid_t owner)
>  {
>  	struct super_block *sb = old->mnt_sb;
>  	struct vfsmount *mnt;
> @@ -554,7 +554,10 @@ static struct vfsmount *clone_mnt(struct
>  	/* don't copy the MNT_USER flag */
>  	mnt->mnt_flags &= ~MNT_USER;
>  	if (flag & CL_SETUSER)
> -		__set_mnt_user(mnt);
> +		__set_mnt_user(mnt, owner);
> +
> +	if (flag & CL_NOSUID)
> +		mnt->mnt_flags |= MNT_NOSUID;
> 
>  	if (flag & CL_SLAVE) {
>  		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
> @@ -1060,7 +1063,7 @@ static int lives_below_in_same_fs(struct
>  }
> 
>  struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
> -					int flag)
> +					int flag, uid_t owner)
>  {
>  	struct vfsmount *res, *p, *q, *r, *s;
>  	struct nameidata nd;
> @@ -1068,7 +1071,7 @@ struct vfsmount *copy_tree(struct vfsmou
>  	if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
>  		return ERR_PTR(-EPERM);
> 
> -	res = q = clone_mnt(mnt, dentry, flag);
> +	res = q = clone_mnt(mnt, dentry, flag, owner);
>  	if (IS_ERR(q))
>  		goto error;
>  	q->mnt_mountpoint = mnt->mnt_mountpoint;
> @@ -1090,7 +1093,7 @@ struct vfsmount *copy_tree(struct vfsmou
>  			p = s;
>  			nd.path.mnt = q;
>  			nd.path.dentry = p->mnt_mountpoint;
> -			q = clone_mnt(p, p->mnt_root, flag);
> +			q = clone_mnt(p, p->mnt_root, flag, owner);
>  			if (IS_ERR(q))
>  				goto error;
>  			spin_lock(&vfsmount_lock);
> @@ -1115,7 +1118,7 @@ struct vfsmount *collect_mounts(struct v
>  {
>  	struct vfsmount *tree;
>  	down_read(&namespace_sem);
> -	tree = copy_tree(mnt, dentry, CL_COPY_ALL | CL_PRIVATE);
> +	tree = copy_tree(mnt, dentry, CL_COPY_ALL | CL_PRIVATE, 0);
>  	up_read(&namespace_sem);
>  	return tree;
>  }
> @@ -1286,7 +1289,8 @@ static int do_change_type(struct nameida
>   */
>  static int do_loopback(struct nameidata *nd, char *old_name, int flags)
>  {
> -	int clone_fl;
> +	int clone_fl = 0;
> +	uid_t owner = 0;
>  	struct nameidata old_nd;
>  	struct vfsmount *mnt = NULL;
>  	int err;
> @@ -1307,11 +1311,17 @@ static int do_loopback(struct nameidata 
>  	if (!check_mnt(nd->path.mnt) || !check_mnt(old_nd.path.mnt))
>  		goto out;
> 
> -	clone_fl = (flags & MS_SETUSER) ? CL_SETUSER : 0;
> +	if (flags & MS_SETUSER) {
> +		clone_fl |= CL_SETUSER;
> +		owner = current->fsuid;
> +	}
> +
>  	if (flags & MS_REC)
> -		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
> +		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl,
> +				owner);
>  	else
> -		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
> +		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl,
> +				owner);
> 
>  	err = PTR_ERR(mnt);
>  	if (IS_ERR(mnt))
> @@ -1535,7 +1545,7 @@ static int do_new_mount(struct nameidata
>  	}
> 
>  	if (flags & MS_SETUSER)
> -		__set_mnt_user(mnt);
> +		__set_mnt_user(mnt, current->fsuid);
> 
>  	return do_add_mount(mnt, nd, mnt_flags, NULL);
> 
> @@ -1931,7 +1941,7 @@ static struct mnt_namespace *dup_mnt_ns(
>  	down_write(&namespace_sem);
>  	/* First pass: copy the tree topology */
>  	new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
> -					CL_COPY_ALL | CL_EXPIRE);
> +					CL_COPY_ALL | CL_EXPIRE, 0);
>  	if (IS_ERR(new_ns->root)) {
>  		up_write(&namespace_sem);
>  		kfree(new_ns);
> Index: linux/fs/pnode.c
> ===================================================================
> --- linux.orig/fs/pnode.c	2008-01-04 13:47:49.000000000 +0100
> +++ linux/fs/pnode.c	2008-01-04 13:49:12.000000000 +0100
> @@ -181,15 +181,28 @@ int propagate_mnt(struct vfsmount *dest_
> 
>  	for (m = propagation_next(dest_mnt, dest_mnt); m;
>  			m = propagation_next(m, dest_mnt)) {
> -		int type;
> +		int clflags;
> +		uid_t owner = 0;
>  		struct vfsmount *source;
> 
>  		if (IS_MNT_NEW(m))
>  			continue;
> 
> -		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
> +		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &clflags);
> 
> -		child = copy_tree(source, source->mnt_root, type);
> +		if (m->mnt_flags & MNT_USER) {
> +			clflags |= CL_SETUSER;
> +			owner = m->mnt_uid;
> +
> +			/*
> +			 * If propagating into a user mount which doesn't
> +			 * allow suid, then make sure, the child(ren) won't
> +			 * allow suid either
> +			 */
> +			if (m->mnt_flags & MNT_NOSUID)
> +				clflags |= CL_NOSUID;
> +		}
> +		child = copy_tree(source, source->mnt_root, clflags, owner);
>  		if (IS_ERR(child)) {
>  			ret = PTR_ERR(child);
>  			list_splice(tree_list, tmp_list.prev);
> Index: linux/fs/pnode.h
> ===================================================================
> --- linux.orig/fs/pnode.h	2008-01-04 13:45:45.000000000 +0100
> +++ linux/fs/pnode.h	2008-01-04 13:49:12.000000000 +0100
> @@ -24,6 +24,7 @@
>  #define CL_PROPAGATION 		0x10
>  #define CL_PRIVATE 		0x20
>  #define CL_SETUSER		0x40
> +#define CL_NOSUID		0x80
> 
>  static inline void set_mnt_shared(struct vfsmount *mnt)
>  {
> @@ -36,4 +37,6 @@ int propagate_mnt(struct vfsmount *, str
>  		struct list_head *);
>  int propagate_umount(struct list_head *);
>  int propagate_mount_busy(struct vfsmount *, int);
> +struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int, uid_t);
> +
>  #endif /* _LINUX_PNODE_H */
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h	2008-01-04 13:48:14.000000000 +0100
> +++ linux/include/linux/fs.h	2008-01-04 13:49:12.000000000 +0100
> @@ -1492,7 +1492,6 @@ extern int may_umount(struct vfsmount *)
>  extern void umount_tree(struct vfsmount *, int, struct list_head *);
>  extern void release_mounts(struct list_head *);
>  extern long do_mount(char *, char *, char *, unsigned long, void *);
> -extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
>  extern void mnt_set_mountpoint(struct vfsmount *, struct dentry *,
>  				  struct vfsmount *);
>  extern struct vfsmount *collect_mounts(struct vfsmount *, struct dentry *);
> 
> --

Re: [patch 8/9] unprivileged mounts: propagation: inherit owner from parent

[Miklos Szeredi]

> Quoting Miklos Szeredi (miklos@szeredi.hu):
> > From: Miklos Szeredi <mszeredi@suse.cz>
> > 
> > On mount propagation, let the owner of the clone be inherited from the
> > parent into which it has been propagated.  Also if the parent has the
> > "nosuid" flag, set this flag for the child as well.
> 
> What about nodev?

Hmm, I think the nosuid thing is meant to prevent suid mounts being
introduced into a "suidless" namespace.  This doesn't apply to dev
mounts, which are quite safe in a suidless environment, as long as the
user is not able to create devices.  But that should be taken care of
by capability tests.

I'll update the description.

Thanks,
Miklos

Re: [patch 8/9] unprivileged mounts: propagation: inherit owner from parent

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> > Quoting Miklos Szeredi (miklos@szeredi.hu):
> > > From: Miklos Szeredi <mszeredi@suse.cz>
> > > 
> > > On mount propagation, let the owner of the clone be inherited from the
> > > parent into which it has been propagated.  Also if the parent has the
> > > "nosuid" flag, set this flag for the child as well.
> > 
> > What about nodev?
> 
> Hmm, I think the nosuid thing is meant to prevent suid mounts being
> introduced into a "suidless" namespace.  This doesn't apply to dev
> mounts, which are quite safe in a suidless environment, as long as the
> user is not able to create devices.  But that should be taken care of
> by capability tests.
> 
> I'll update the description.

Hmm,

Part of me wants to say the safest thing for now would be to refuse
mounts propagation from non-user mounts to user mounts.

I assume you're thinking about a fully user-mounted chroot, where
the user woudl still want to be able to stick in a cdrom and have
it automounted under /mnt/cdrom, propagated from the root mounts ns?

But then are there no devices which the user could create on a floppy
while inserted into his own laptop, owned by his own uid, then insert
into this machine, and use the device under the auto-mounted /dev/floppy
to gain inappropriate access?

-serge

Re: [patch 8/9] unprivileged mounts: propagation: inherit owner from parent

[Miklos Szeredi]

> > > > On mount propagation, let the owner of the clone be inherited from the
> > > > parent into which it has been propagated.  Also if the parent has the
> > > > "nosuid" flag, set this flag for the child as well.
> > > 
> > > What about nodev?
> > 
> > Hmm, I think the nosuid thing is meant to prevent suid mounts being
> > introduced into a "suidless" namespace.  This doesn't apply to dev
> > mounts, which are quite safe in a suidless environment, as long as the
> > user is not able to create devices.  But that should be taken care of
> > by capability tests.
> > 
> > I'll update the description.
> 
> Hmm,
> 
> Part of me wants to say the safest thing for now would be to refuse
> mounts propagation from non-user mounts to user mounts.
> 
> I assume you're thinking about a fully user-mounted chroot, where
> the user woudl still want to be able to stick in a cdrom and have
> it automounted under /mnt/cdrom, propagated from the root mounts ns?

Right.

> But then are there no devices which the user could create on a floppy
> while inserted into his own laptop, owned by his own uid, then insert
> into this machine, and use the device under the auto-mounted /dev/floppy
> to gain inappropriate access?

I assume, that the floppy and cdrom are already mounted with
nosuid,nodev.

The problem case is I think is if a sysadmin does some mounting in the
initial namespace, and this is propagated into the fully user-mounted
namespace (or chroot), so that a mount with suid binaries slips in.
Which is bad, because the user may be able rearange the namespace, to
trick the suid program to something it should not do.

OTOH, a mount with devices can't be abused this way, since it is not
possible to gain privileges to files/devices just by rearanging the
mounts.

Miklos

Re: [patch 8/9] unprivileged mounts: propagation: inherit owner from parent

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> > > > > On mount propagation, let the owner of the clone be inherited from the
> > > > > parent into which it has been propagated.  Also if the parent has the
> > > > > "nosuid" flag, set this flag for the child as well.
> > > > 
> > > > What about nodev?
> > > 
> > > Hmm, I think the nosuid thing is meant to prevent suid mounts being
> > > introduced into a "suidless" namespace.  This doesn't apply to dev
> > > mounts, which are quite safe in a suidless environment, as long as the
> > > user is not able to create devices.  But that should be taken care of
> > > by capability tests.
> > > 
> > > I'll update the description.
> > 
> > Hmm,
> > 
> > Part of me wants to say the safest thing for now would be to refuse
> > mounts propagation from non-user mounts to user mounts.
> > 
> > I assume you're thinking about a fully user-mounted chroot, where
> > the user woudl still want to be able to stick in a cdrom and have
> > it automounted under /mnt/cdrom, propagated from the root mounts ns?
> 
> Right.
> 
> > But then are there no devices which the user could create on a floppy
> > while inserted into his own laptop, owned by his own uid, then insert
> > into this machine, and use the device under the auto-mounted /dev/floppy
> > to gain inappropriate access?
> 
> I assume, that the floppy and cdrom are already mounted with
> nosuid,nodev.

Yeah, of course, what I'm saying is no different whether the upper mount
is a user mount or not.  You're right.

> The problem case is I think is if a sysadmin does some mounting in the
> initial namespace, and this is propagated into the fully user-mounted
> namespace (or chroot), so that a mount with suid binaries slips in.
> Which is bad, because the user may be able rearange the namespace, to
> trick the suid program to something it should not do.

And really this shouldn't be an issue at all - the usermount chroot
would be set up under something like /share/hallyn/root, so the admin
would have to purposely set up propagation into that tree, so this
won't be happening by accident.

> OTOH, a mount with devices can't be abused this way, since it is not
> possible to gain privileges to files/devices just by rearanging the
> mounts.

Thanks for humoring me,

-serge

[patch 9/9] unprivileged mounts: add "no submounts" flag

[Miklos Szeredi]

[-- Attachment #1: unprivileged-mounts-add-no-submounts-flag.patch --]
[-- Type: text/plain, Size: 2856 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Add a new mount flag "nomnt", which denies submounts for the owner.
This would be useful, if we want to support traditional /etc/fstab
based user mounts.

In this case mount(8) would still have to be suid-root, to check the
mountpoint against the user/users flag in /etc/fstab, but /etc/mtab
would no longer be mandatory for storing the actual owner of the
mount.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-04 13:49:52.000000000 +0100
+++ linux/fs/namespace.c	2008-01-04 13:50:28.000000000 +0100
@@ -694,6 +694,7 @@ static int show_vfsmnt(struct seq_file *
 		{ MNT_NOATIME, ",noatime" },
 		{ MNT_NODIRATIME, ",nodiratime" },
 		{ MNT_RELATIME, ",relatime" },
+		{ MNT_NOMNT, ",nomnt" },
 		{ 0, NULL }
 	};
 	struct proc_fs_info *fs_infop;
@@ -1044,6 +1045,9 @@ static bool permit_mount(struct nameidat
 	if (S_ISLNK(inode->i_mode))
 		return false;
 
+	if (nd->path.mnt->mnt_flags & MNT_NOMNT)
+		return false;
+
 	if (!is_mount_owner(nd->path.mnt, current->fsuid))
 		return false;
 
@@ -1888,9 +1892,11 @@ long do_mount(char *dev_name, char *dir_
 		mnt_flags |= MNT_RELATIME;
 	if (flags & MS_RDONLY)
 		mnt_flags |= MNT_READONLY;
+	if (flags & MS_NOMNT)
+		mnt_flags |= MNT_NOMNT;
 
-	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
-		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT);
+	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_NOATIME |
+			MS_NODIRATIME | MS_RELATIME | MS_KERNMOUNT | MS_NOMNT);
 
 	/* ... and get the mountpoint */
 	retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h	2008-01-04 13:49:12.000000000 +0100
+++ linux/include/linux/fs.h	2008-01-04 13:49:58.000000000 +0100
@@ -130,6 +130,7 @@ extern int dir_notify_enable;
 #define MS_KERNMOUNT	(1<<22) /* this is a kern_mount call */
 #define MS_I_VERSION	(1<<23) /* Update inode I_version field */
 #define MS_SETUSER	(1<<24) /* set mnt_uid to current user */
+#define MS_NOMNT	(1<<25) /* don't allow unprivileged submounts */
 #define MS_ACTIVE	(1<<30)
 #define MS_NOUSER	(1<<31)
 
Index: linux/include/linux/mount.h
===================================================================
--- linux.orig/include/linux/mount.h	2008-01-04 13:45:45.000000000 +0100
+++ linux/include/linux/mount.h	2008-01-04 13:49:58.000000000 +0100
@@ -30,6 +30,7 @@ struct mnt_namespace;
 #define MNT_NODIRATIME	0x10
 #define MNT_RELATIME	0x20
 #define MNT_READONLY	0x40	/* does the user want this to be r/o? */
+#define MNT_NOMNT	0x80
 
 #define MNT_SHRINKABLE	0x100
 #define MNT_IMBALANCED_WRITE_COUNT	0x200 /* just for debugging */

--

Re: [patch 9/9] unprivileged mounts: add "no submounts" flag

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Add a new mount flag "nomnt", which denies submounts for the owner.
> This would be useful, if we want to support traditional /etc/fstab
> based user mounts.
> 
> In this case mount(8) would still have to be suid-root, to check the
> mountpoint against the user/users flag in /etc/fstab, but /etc/mtab
> would no longer be mandatory for storing the actual owner of the
> mount.

Ah, I see, so the floppy drive could be mounted as a MNT_NOMNT but
MNT_USER mount with mnt_owner set.  Makes sense.  I'd ask for a better
name than 'nomnt', but I can't think of one myself.

> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Acked-by: Serge Hallyn <serue@us.ibm.com>

> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-04 13:49:52.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-04 13:50:28.000000000 +0100
> @@ -694,6 +694,7 @@ static int show_vfsmnt(struct seq_file *
>  		{ MNT_NOATIME, ",noatime" },
>  		{ MNT_NODIRATIME, ",nodiratime" },
>  		{ MNT_RELATIME, ",relatime" },
> +		{ MNT_NOMNT, ",nomnt" },
>  		{ 0, NULL }
>  	};
>  	struct proc_fs_info *fs_infop;
> @@ -1044,6 +1045,9 @@ static bool permit_mount(struct nameidat
>  	if (S_ISLNK(inode->i_mode))
>  		return false;
> 
> +	if (nd->path.mnt->mnt_flags & MNT_NOMNT)
> +		return false;
> +
>  	if (!is_mount_owner(nd->path.mnt, current->fsuid))
>  		return false;
> 
> @@ -1888,9 +1892,11 @@ long do_mount(char *dev_name, char *dir_
>  		mnt_flags |= MNT_RELATIME;
>  	if (flags & MS_RDONLY)
>  		mnt_flags |= MNT_READONLY;
> +	if (flags & MS_NOMNT)
> +		mnt_flags |= MNT_NOMNT;
> 
> -	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
> -		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT);
> +	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_NOATIME |
> +			MS_NODIRATIME | MS_RELATIME | MS_KERNMOUNT | MS_NOMNT);
> 
>  	/* ... and get the mountpoint */
>  	retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h	2008-01-04 13:49:12.000000000 +0100
> +++ linux/include/linux/fs.h	2008-01-04 13:49:58.000000000 +0100
> @@ -130,6 +130,7 @@ extern int dir_notify_enable;
>  #define MS_KERNMOUNT	(1<<22) /* this is a kern_mount call */
>  #define MS_I_VERSION	(1<<23) /* Update inode I_version field */
>  #define MS_SETUSER	(1<<24) /* set mnt_uid to current user */
> +#define MS_NOMNT	(1<<25) /* don't allow unprivileged submounts */
>  #define MS_ACTIVE	(1<<30)
>  #define MS_NOUSER	(1<<31)
> 
> Index: linux/include/linux/mount.h
> ===================================================================
> --- linux.orig/include/linux/mount.h	2008-01-04 13:45:45.000000000 +0100
> +++ linux/include/linux/mount.h	2008-01-04 13:49:58.000000000 +0100
> @@ -30,6 +30,7 @@ struct mnt_namespace;
>  #define MNT_NODIRATIME	0x10
>  #define MNT_RELATIME	0x20
>  #define MNT_READONLY	0x40	/* does the user want this to be r/o? */
> +#define MNT_NOMNT	0x80
> 
>  #define MNT_SHRINKABLE	0x100
>  #define MNT_IMBALANCED_WRITE_COUNT	0x200 /* just for debugging */
> 
> --

Re: [patch 9/9] unprivileged mounts: add "no submounts" flag

[Miklos Szeredi]

> Quoting Miklos Szeredi (miklos@szeredi.hu):
> > From: Miklos Szeredi <mszeredi@suse.cz>
> > 
> > Add a new mount flag "nomnt", which denies submounts for the owner.
> > This would be useful, if we want to support traditional /etc/fstab
> > based user mounts.
> > 
> > In this case mount(8) would still have to be suid-root, to check the
> > mountpoint against the user/users flag in /etc/fstab, but /etc/mtab
> > would no longer be mandatory for storing the actual owner of the
> > mount.
> 
> Ah, I see, so the floppy drive could be mounted as a MNT_NOMNT but
> MNT_USER mount with mnt_owner set.  Makes sense.  I'd ask for a better
> name than 'nomnt', but I can't think of one myself.

Me neither.

Thanks for the review, Serge!

Miklos

Re: [patch 9/9] unprivileged mounts: add "no submounts" flag

[A. C. Censi]

On Jan 15, 2008 8:41 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> > Quoting Miklos Szeredi (miklos@szeredi.hu):
> > > From: Miklos Szeredi <mszeredi@suse.cz>
> > >
> > > Add a new mount flag "nomnt", which denies submounts for the owner.
> > > This would be useful, if we want to support traditional /etc/fstab
> > > based user mounts.
> > >
> > > In this case mount(8) would still have to be suid-root, to check the
> > > mountpoint against the user/users flag in /etc/fstab, but /etc/mtab
> > > would no longer be mandatory for storing the actual owner of the
> > > mount.
> >
> > Ah, I see, so the floppy drive could be mounted as a MNT_NOMNT but
> > MNT_USER mount with mnt_owner set.  Makes sense.  I'd ask for a better
> > name than 'nomnt', but I can't think of one myself.
>
> Me neither.
>

Why not "nosubmnt"?


-- 
A. C. Censi
accensi [em] gmail [ponto] com
accensi [em] montreal [ponto] com [ponto] br

Re: [patch 9/9] unprivileged mounts: add "no submounts" flag

[Miklos Szeredi]

> Why not "nosubmnt"?

Why not indeed.  Maybe I should try to use my brain sometime.

Thanks,
Miklos

Re: [patch 9/9] unprivileged mounts: add "no submounts" flag

[Serge E. Hallyn]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> > Why not "nosubmnt"?
> 
> Why not indeed.  Maybe I should try to use my brain sometime.

Well it really should have 'user' or 'unpriv' in the name
somewhere.  'nosubmnt' is more confusing than 'nomnt' because
it no submounts really sounds like a reasonable thing in
itself...

But I never win naming arguments, so I accept that I have poor
naming judgement  :)

-serge

Re: [patch 9/9] unprivileged mounts: add "no submounts" flag

[Miklos Szeredi]

> > > Why not "nosubmnt"?
> > 
> > Why not indeed.  Maybe I should try to use my brain sometime.
> 
> Well it really should have 'user' or 'unpriv' in the name
> somewhere.  'nosubmnt' is more confusing than 'nomnt' because
> it no submounts really sounds like a reasonable thing in
> itself...

I slept on it, and I still think 'nosubmnt' might be the best
compromise.  Obviously the superuser has privileges, that override
what is normally allowed, and we don't find it strange when a
read-only file is happily being written by root.

It may feel wrong in the context of mounts, because we are so used to
mounts being privileged-only.

Objections?  Once this goes in, it will stay the same forever, so now
is the time to express any doubts...

Thanks,
Miklos