[PATCH 00/19] Support fuse mounts in user namespaces

[PATCH 00/19] Support fuse mounts in user namespaces

[Seth Forshee]

These patches implement support for mounting filesystems in user
namespaces using fuse. I've sent the full set of patches this time
because I feel that previous discussions could have benefited from more
context. I've also dropped any patches from my previous postings not
specifically required for fuse mounts.

These are based on the patches in the for-testing branch of
git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git,
but I've rebased them onto 4.4-rc3. I've pushed all of this to:

 git://git.kernel.org/pub/scm/linux/kernel/git/sforshee/linux.git fuse-userns

The patches are organized into three high-level groups.

Patches 1-6 are related to security, adding restrictions for
unprivileged mounts and updating the LSMs as needed. Patches 1-2
(checking inode permissions for block device mounts) may not be strictly
necessary for fuseblk mounts since fuse doesn't do any IO on the block
device in the kernel, but it still seems like a good idea to fail the
mount if the user doesn't have the required permissions for the inode
(though this is a bit misleading with fuse since the mounts are done via
a suid-root helper).

Patches 7-15 update most of the vfs to translate ids correctly and deal
with inodes which may have invalid user/group ids. I've omitted patches
for anything not used by fuse - quota, fs freezing, some helper
functions, etc. - but if these are wanted for the sake of completeness I
can include them.

Patches 16-19 update fuse to deal with mounts from non-init pid and user
namespaces and enable mounting from user namespaces.

Thanks,
Seth

Andy Lutomirski (1):
  fs: Treat foreign mounts as nosuid

Seth Forshee (18):
  block_dev: Support checking inode permissions in lookup_bdev()
  block_dev: Check permissions towards block device inode when mounting
  selinux: Add support for unprivileged mounts from user namespaces
  userns: Replace in_userns with current_in_userns
  Smack: Handle labels consistently in untrusted mounts
  fs: Check for invalid i_uid in may_follow_link()
  cred: Reject inodes with invalid ids in set_create_file_as()
  fs: Refuse uid/gid changes which don't map into s_user_ns
  fs: Update posix_acl support to handle user namespace mounts
  fs: Ensure the mounter of a filesystem is privileged towards its
    inodes
  fs: Don't remove suid for CAP_FSETID in s_user_ns
  fs: Allow superblock owner to access do_remount_sb()
  fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns
  capabilities: Allow privileged user in s_user_ns to set file caps
  fuse: Add support for pid namespaces
  fuse: Support fuse filesystems outside of init_user_ns
  fuse: Restrict allow_other to the superblock's namespace or a
    descendant
  fuse: Allow user namespace mounts

 drivers/md/bcache/super.c       |  2 +-
 drivers/md/dm-table.c           |  2 +-
 drivers/mtd/mtdsuper.c          |  2 +-
 fs/attr.c                       | 11 +++++
 fs/block_dev.c                  | 18 ++++++--
 fs/exec.c                       |  2 +-
 fs/fuse/cuse.c                  |  3 +-
 fs/fuse/dev.c                   | 26 +++++++++---
 fs/fuse/dir.c                   | 91 ++++++++++++++++++++++++++--------------
 fs/fuse/file.c                  | 22 +++++++---
 fs/fuse/fuse_i.h                | 18 +++++---
 fs/fuse/inode.c                 | 92 ++++++++++++++++++++++++++++++-----------
 fs/inode.c                      |  6 ++-
 fs/ioctl.c                      |  2 +-
 fs/namei.c                      |  2 +-
 fs/namespace.c                  | 17 +++++++-
 fs/posix_acl.c                  | 67 +++++++++++++++++++-----------
 fs/quota/quota.c                |  2 +-
 fs/xattr.c                      | 19 ++++++---
 include/linux/fs.h              |  2 +-
 include/linux/mount.h           |  1 +
 include/linux/posix_acl_xattr.h | 17 ++++++--
 include/linux/uidgid.h          | 10 +++++
 include/linux/user_namespace.h  |  6 +--
 kernel/capability.c             | 13 ++++--
 kernel/cred.c                   |  2 +
 kernel/user_namespace.c         |  6 +--
 security/commoncap.c            | 16 ++++---
 security/selinux/hooks.c        | 25 ++++++++++-
 security/smack/smack_lsm.c      | 29 ++++++++-----
 30 files changed, 386 insertions(+), 145 deletions(-)

[PATCH 01/19] block_dev: Support checking inode permissions in lookup_bdev()

[Seth Forshee]

When looking up a block device by path no permission check is
done to verify that the user has access to the block device inode
at the specified path. In some cases it may be necessary to
check permissions towards the inode, such as allowing
unprivileged users to mount block devices in user namespaces.

Add an argument to lookup_bdev() to optionally perform this
permission check. A value of 0 skips the permission check and
behaves the same as before. A non-zero value specifies the mask
of access rights required towards the inode at the specified
path. The check is always skipped if the user has CAP_SYS_ADMIN.

All callers of lookup_bdev() currently pass a mask of 0, so this
patch results in no functional change. Subsequent patches will
add permission checks where appropriate.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 drivers/md/bcache/super.c |  2 +-
 drivers/md/dm-table.c     |  2 +-
 drivers/mtd/mtdsuper.c    |  2 +-
 fs/block_dev.c            | 13 ++++++++++---
 fs/quota/quota.c          |  2 +-
 include/linux/fs.h        |  2 +-
 6 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 679a093a3bf6..e8287b0d1dac 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1926,7 +1926,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 				  sb);
 	if (IS_ERR(bdev)) {
 		if (bdev == ERR_PTR(-EBUSY)) {
-			bdev = lookup_bdev(strim(path));
+			bdev = lookup_bdev(strim(path), 0);
 			mutex_lock(&bch_register_lock);
 			if (!IS_ERR(bdev) && bch_is_open(bdev))
 				err = "device already registered";
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 061152a43730..81c60b2495ed 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -380,7 +380,7 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 	BUG_ON(!t);
 
 	/* convert the path to a device */
-	bdev = lookup_bdev(path);
+	bdev = lookup_bdev(path, 0);
 	if (IS_ERR(bdev)) {
 		dev = name_to_dev_t(path);
 		if (!dev)
diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c
index 20c02a3b7417..b5b60e1af31c 100644
--- a/drivers/mtd/mtdsuper.c
+++ b/drivers/mtd/mtdsuper.c
@@ -176,7 +176,7 @@ struct dentry *mount_mtd(struct file_system_type *fs_type, int flags,
 	/* try the old way - the hack where we allowed users to mount
 	 * /dev/mtdblock$(n) but didn't actually _use_ the blockdev
 	 */
-	bdev = lookup_bdev(dev_name);
+	bdev = lookup_bdev(dev_name, 0);
 	if (IS_ERR(bdev)) {
 		ret = PTR_ERR(bdev);
 		pr_debug("MTDSB: lookup_bdev() returned %d\n", ret);
diff --git a/fs/block_dev.c b/fs/block_dev.c
index f90d91efa1b4..3ebbde85d898 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1426,7 +1426,7 @@ struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
 	struct block_device *bdev;
 	int err;
 
-	bdev = lookup_bdev(path);
+	bdev = lookup_bdev(path, 0);
 	if (IS_ERR(bdev))
 		return bdev;
 
@@ -1736,12 +1736,14 @@ EXPORT_SYMBOL(ioctl_by_bdev);
 /**
  * lookup_bdev  - lookup a struct block_device by name
  * @pathname:	special file representing the block device
+ * @mask:	rights to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
  *
  * Get a reference to the blockdevice at @pathname in the current
  * namespace if possible and return it.  Return ERR_PTR(error)
- * otherwise.
+ * otherwise.  If @mask is non-zero, check for access rights to the
+ * inode at @pathname.
  */
-struct block_device *lookup_bdev(const char *pathname)
+struct block_device *lookup_bdev(const char *pathname, int mask)
 {
 	struct block_device *bdev;
 	struct inode *inode;
@@ -1756,6 +1758,11 @@ struct block_device *lookup_bdev(const char *pathname)
 		return ERR_PTR(error);
 
 	inode = d_backing_inode(path.dentry);
+	if (mask != 0 && !capable(CAP_SYS_ADMIN)) {
+		error = __inode_permission(inode, mask);
+		if (error)
+			goto fail;
+	}
 	error = -ENOTBLK;
 	if (!S_ISBLK(inode->i_mode))
 		goto fail;
diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index 3746367098fd..a40eaecbd5cc 100644
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -733,7 +733,7 @@ static struct super_block *quotactl_block(const char __user *special, int cmd)
 
 	if (IS_ERR(tmp))
 		return ERR_CAST(tmp);
-	bdev = lookup_bdev(tmp->name);
+	bdev = lookup_bdev(tmp->name, 0);
 	putname(tmp);
 	if (IS_ERR(bdev))
 		return ERR_CAST(bdev);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8a17c5649ef2..879ec382fd88 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2373,7 +2373,7 @@ static inline void unregister_chrdev(unsigned int major, const char *name)
 #define BLKDEV_MAJOR_HASH_SIZE	255
 extern const char *__bdevname(dev_t, char *buffer);
 extern const char *bdevname(struct block_device *bdev, char *buffer);
-extern struct block_device *lookup_bdev(const char *);
+extern struct block_device *lookup_bdev(const char *, int mask);
 extern void blkdev_show(struct seq_file *,off_t);
 
 #else
-- 
1.9.1

Re: [PATCH 01/19] block_dev: Support checking inode permissions in lookup_bdev()

[Serge E. Hallyn]

On Wed, Dec 02, 2015 at 09:40:01AM -0600, Seth Forshee wrote:
> When looking up a block device by path no permission check is
> done to verify that the user has access to the block device inode
> at the specified path. In some cases it may be necessary to
> check permissions towards the inode, such as allowing
> unprivileged users to mount block devices in user namespaces.
> 
> Add an argument to lookup_bdev() to optionally perform this
> permission check. A value of 0 skips the permission check and
> behaves the same as before. A non-zero value specifies the mask
> of access rights required towards the inode at the specified
> path. The check is always skipped if the user has CAP_SYS_ADMIN.
> 
> All callers of lookup_bdev() currently pass a mask of 0, so this
> patch results in no functional change. Subsequent patches will
> add permission checks where appropriate.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  drivers/md/bcache/super.c |  2 +-
>  drivers/md/dm-table.c     |  2 +-
>  drivers/mtd/mtdsuper.c    |  2 +-
>  fs/block_dev.c            | 13 ++++++++++---
>  fs/quota/quota.c          |  2 +-
>  include/linux/fs.h        |  2 +-
>  6 files changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 679a093a3bf6..e8287b0d1dac 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1926,7 +1926,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>  				  sb);
>  	if (IS_ERR(bdev)) {
>  		if (bdev == ERR_PTR(-EBUSY)) {
> -			bdev = lookup_bdev(strim(path));
> +			bdev = lookup_bdev(strim(path), 0);
>  			mutex_lock(&bch_register_lock);
>  			if (!IS_ERR(bdev) && bch_is_open(bdev))
>  				err = "device already registered";
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 061152a43730..81c60b2495ed 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -380,7 +380,7 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
>  	BUG_ON(!t);
>  
>  	/* convert the path to a device */
> -	bdev = lookup_bdev(path);
> +	bdev = lookup_bdev(path, 0);
>  	if (IS_ERR(bdev)) {
>  		dev = name_to_dev_t(path);
>  		if (!dev)
> diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c
> index 20c02a3b7417..b5b60e1af31c 100644
> --- a/drivers/mtd/mtdsuper.c
> +++ b/drivers/mtd/mtdsuper.c
> @@ -176,7 +176,7 @@ struct dentry *mount_mtd(struct file_system_type *fs_type, int flags,
>  	/* try the old way - the hack where we allowed users to mount
>  	 * /dev/mtdblock$(n) but didn't actually _use_ the blockdev
>  	 */
> -	bdev = lookup_bdev(dev_name);
> +	bdev = lookup_bdev(dev_name, 0);
>  	if (IS_ERR(bdev)) {
>  		ret = PTR_ERR(bdev);
>  		pr_debug("MTDSB: lookup_bdev() returned %d\n", ret);
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index f90d91efa1b4..3ebbde85d898 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1426,7 +1426,7 @@ struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
>  	struct block_device *bdev;
>  	int err;
>  
> -	bdev = lookup_bdev(path);
> +	bdev = lookup_bdev(path, 0);
>  	if (IS_ERR(bdev))
>  		return bdev;
>  
> @@ -1736,12 +1736,14 @@ EXPORT_SYMBOL(ioctl_by_bdev);
>  /**
>   * lookup_bdev  - lookup a struct block_device by name
>   * @pathname:	special file representing the block device
> + * @mask:	rights to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
>   *
>   * Get a reference to the blockdevice at @pathname in the current
>   * namespace if possible and return it.  Return ERR_PTR(error)
> - * otherwise.
> + * otherwise.  If @mask is non-zero, check for access rights to the
> + * inode at @pathname.
>   */
> -struct block_device *lookup_bdev(const char *pathname)
> +struct block_device *lookup_bdev(const char *pathname, int mask)
>  {
>  	struct block_device *bdev;
>  	struct inode *inode;
> @@ -1756,6 +1758,11 @@ struct block_device *lookup_bdev(const char *pathname)
>  		return ERR_PTR(error);
>  
>  	inode = d_backing_inode(path.dentry);
> +	if (mask != 0 && !capable(CAP_SYS_ADMIN)) {
> +		error = __inode_permission(inode, mask);
> +		if (error)
> +			goto fail;
> +	}
>  	error = -ENOTBLK;
>  	if (!S_ISBLK(inode->i_mode))
>  		goto fail;
> diff --git a/fs/quota/quota.c b/fs/quota/quota.c
> index 3746367098fd..a40eaecbd5cc 100644
> --- a/fs/quota/quota.c
> +++ b/fs/quota/quota.c
> @@ -733,7 +733,7 @@ static struct super_block *quotactl_block(const char __user *special, int cmd)
>  
>  	if (IS_ERR(tmp))
>  		return ERR_CAST(tmp);
> -	bdev = lookup_bdev(tmp->name);
> +	bdev = lookup_bdev(tmp->name, 0);
>  	putname(tmp);
>  	if (IS_ERR(bdev))
>  		return ERR_CAST(bdev);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 8a17c5649ef2..879ec382fd88 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2373,7 +2373,7 @@ static inline void unregister_chrdev(unsigned int major, const char *name)
>  #define BLKDEV_MAJOR_HASH_SIZE	255
>  extern const char *__bdevname(dev_t, char *buffer);
>  extern const char *bdevname(struct block_device *bdev, char *buffer);
> -extern struct block_device *lookup_bdev(const char *);
> +extern struct block_device *lookup_bdev(const char *, int mask);
>  extern void blkdev_show(struct seq_file *,off_t);
>  
>  #else
> -- 
> 1.9.1
> 
> --
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> Please read the FAQ at  http://www.tux.org/lkml/

[PATCH 02/19] block_dev: Check permissions towards block device inode when mounting

[Seth Forshee]

Unprivileged users should not be able to mount block devices when
they lack sufficient privileges towards the block device inode.
Update blkdev_get_by_path() to validate that the user has the
required access to the inode at the specified path. The check
will be skipped for CAP_SYS_ADMIN, so privileged mounts will
continue working as before.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/block_dev.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 3ebbde85d898..4fdb6ab59816 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1424,9 +1424,14 @@ struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
 					void *holder)
 {
 	struct block_device *bdev;
+	int perm = 0;
 	int err;
 
-	bdev = lookup_bdev(path, 0);
+	if (mode & FMODE_READ)
+		perm |= MAY_READ;
+	if (mode & FMODE_WRITE)
+		perm |= MAY_WRITE;
+	bdev = lookup_bdev(path, perm);
 	if (IS_ERR(bdev))
 		return bdev;
 
-- 
1.9.1

Re: [PATCH 02/19] block_dev: Check permissions towards block device inode when mounting

[Serge E. Hallyn]

On Wed, Dec 02, 2015 at 09:40:02AM -0600, Seth Forshee wrote:
> Unprivileged users should not be able to mount block devices when
> they lack sufficient privileges towards the block device inode.
> Update blkdev_get_by_path() to validate that the user has the
> required access to the inode at the specified path. The check
> will be skipped for CAP_SYS_ADMIN, so privileged mounts will
> continue working as before.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/block_dev.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 3ebbde85d898..4fdb6ab59816 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1424,9 +1424,14 @@ struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
>  					void *holder)
>  {
>  	struct block_device *bdev;
> +	int perm = 0;
>  	int err;
>  
> -	bdev = lookup_bdev(path, 0);
> +	if (mode & FMODE_READ)
> +		perm |= MAY_READ;
> +	if (mode & FMODE_WRITE)
> +		perm |= MAY_WRITE;
> +	bdev = lookup_bdev(path, perm);
>  	if (IS_ERR(bdev))
>  		return bdev;
>  
> -- 
> 1.9.1
> 
> --
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> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

[PATCH 03/19] fs: Treat foreign mounts as nosuid

[Seth Forshee]

From: Andy Lutomirski <luto@amacapital.net>

If a process gets access to a mount from a different user
namespace, that process should not be able to take advantage of
setuid files or selinux entrypoints from that filesystem.  Prevent
this by treating mounts from other mount namespaces and those not
owned by current_user_ns() or an ancestor as nosuid.

This will make it safer to allow more complex filesystems to be
mounted in non-root user namespaces.

This does not remove the need for MNT_LOCK_NOSUID.  The setuid,
setgid, and file capability bits can no longer be abused if code in
a user namespace were to clear nosuid on an untrusted filesystem,
but this patch, by itself, is insufficient to protect the system
from abuse of files that, when execed, would increase MAC privilege.

As a more concrete explanation, any task that can manipulate a
vfsmount associated with a given user namespace already has
capabilities in that namespace and all of its descendents.  If they
can cause a malicious setuid, setgid, or file-caps executable to
appear in that mount, then that executable will only allow them to
elevate privileges in exactly the set of namespaces in which they
are already privileges.

On the other hand, if they can cause a malicious executable to
appear with a dangerous MAC label, running it could change the
caller's security context in a way that should not have been
possible, even inside the namespace in which the task is confined.

As a hardening measure, this would have made CVE-2014-5207 much
more difficult to exploit.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: James Morris <james.l.morris@oracle.com>
---
 fs/exec.c                |  2 +-
 fs/namespace.c           | 13 +++++++++++++
 include/linux/mount.h    |  1 +
 security/commoncap.c     |  2 +-
 security/selinux/hooks.c |  2 +-
 5 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index b06623a9347f..ea7311d72cc3 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1295,7 +1295,7 @@ static void bprm_fill_uid(struct linux_binprm *bprm)
 	bprm->cred->euid = current_euid();
 	bprm->cred->egid = current_egid();
 
-	if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
+	if (!mnt_may_suid(bprm->file->f_path.mnt))
 		return;
 
 	if (task_no_new_privs(current))
diff --git a/fs/namespace.c b/fs/namespace.c
index da70f7c4ece1..2101ce7b96ab 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3276,6 +3276,19 @@ found:
 	return visible;
 }
 
+bool mnt_may_suid(struct vfsmount *mnt)
+{
+	/*
+	 * Foreign mounts (accessed via fchdir or through /proc
+	 * symlinks) are always treated as if they are nosuid.  This
+	 * prevents namespaces from trusting potentially unsafe
+	 * suid/sgid bits, file caps, or security labels that originate
+	 * in other namespaces.
+	 */
+	return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
+	       in_userns(current_user_ns(), mnt->mnt_sb->s_user_ns);
+}
+
 static struct ns_common *mntns_get(struct task_struct *task)
 {
 	struct ns_common *ns = NULL;
diff --git a/include/linux/mount.h b/include/linux/mount.h
index f822c3c11377..54a594d49733 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -81,6 +81,7 @@ extern void mntput(struct vfsmount *mnt);
 extern struct vfsmount *mntget(struct vfsmount *mnt);
 extern struct vfsmount *mnt_clone_internal(struct path *path);
 extern int __mnt_is_readonly(struct vfsmount *mnt);
+extern bool mnt_may_suid(struct vfsmount *mnt);
 
 struct path;
 extern struct vfsmount *clone_private_mount(struct path *path);
diff --git a/security/commoncap.c b/security/commoncap.c
index 400aa224b491..6243aef5860e 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -448,7 +448,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
 	if (!file_caps_enabled)
 		return 0;
 
-	if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
+	if (!mnt_may_suid(bprm->file->f_path.mnt))
 		return 0;
 	if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns))
 		return 0;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index d0cfaa9f19d0..a5b93df6553f 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2171,7 +2171,7 @@ static int check_nnp_nosuid(const struct linux_binprm *bprm,
 			    const struct task_security_struct *new_tsec)
 {
 	int nnp = (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS);
-	int nosuid = (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID);
+	int nosuid = !mnt_may_suid(bprm->file->f_path.mnt);
 	int rc;
 
 	if (!nnp && !nosuid)
-- 
1.9.1

Re: [PATCH 03/19] fs: Treat foreign mounts as nosuid

[Serge E. Hallyn]

On Wed, Dec 02, 2015 at 09:40:03AM -0600, Seth Forshee wrote:
> From: Andy Lutomirski <luto@amacapital.net>
> 
> If a process gets access to a mount from a different user
> namespace, that process should not be able to take advantage of
> setuid files or selinux entrypoints from that filesystem.  Prevent
> this by treating mounts from other mount namespaces and those not
> owned by current_user_ns() or an ancestor as nosuid.
> 
> This will make it safer to allow more complex filesystems to be
> mounted in non-root user namespaces.
> 
> This does not remove the need for MNT_LOCK_NOSUID.  The setuid,
> setgid, and file capability bits can no longer be abused if code in
> a user namespace were to clear nosuid on an untrusted filesystem,
> but this patch, by itself, is insufficient to protect the system
> from abuse of files that, when execed, would increase MAC privilege.
> 
> As a more concrete explanation, any task that can manipulate a
> vfsmount associated with a given user namespace already has
> capabilities in that namespace and all of its descendents.  If they
> can cause a malicious setuid, setgid, or file-caps executable to
> appear in that mount, then that executable will only allow them to
> elevate privileges in exactly the set of namespaces in which they
> are already privileges.
> 
> On the other hand, if they can cause a malicious executable to
> appear with a dangerous MAC label, running it could change the
> caller's security context in a way that should not have been
> possible, even inside the namespace in which the task is confined.
> 
> As a hardening measure, this would have made CVE-2014-5207 much
> more difficult to exploit.
> 
> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> Acked-by: James Morris <james.l.morris@oracle.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/exec.c                |  2 +-
>  fs/namespace.c           | 13 +++++++++++++
>  include/linux/mount.h    |  1 +
>  security/commoncap.c     |  2 +-
>  security/selinux/hooks.c |  2 +-
>  5 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index b06623a9347f..ea7311d72cc3 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1295,7 +1295,7 @@ static void bprm_fill_uid(struct linux_binprm *bprm)
>  	bprm->cred->euid = current_euid();
>  	bprm->cred->egid = current_egid();
>  
> -	if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
> +	if (!mnt_may_suid(bprm->file->f_path.mnt))
>  		return;
>  
>  	if (task_no_new_privs(current))
> diff --git a/fs/namespace.c b/fs/namespace.c
> index da70f7c4ece1..2101ce7b96ab 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -3276,6 +3276,19 @@ found:
>  	return visible;
>  }
>  
> +bool mnt_may_suid(struct vfsmount *mnt)
> +{
> +	/*
> +	 * Foreign mounts (accessed via fchdir or through /proc
> +	 * symlinks) are always treated as if they are nosuid.  This
> +	 * prevents namespaces from trusting potentially unsafe
> +	 * suid/sgid bits, file caps, or security labels that originate
> +	 * in other namespaces.
> +	 */
> +	return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
> +	       in_userns(current_user_ns(), mnt->mnt_sb->s_user_ns);
> +}
> +
>  static struct ns_common *mntns_get(struct task_struct *task)
>  {
>  	struct ns_common *ns = NULL;
> diff --git a/include/linux/mount.h b/include/linux/mount.h
> index f822c3c11377..54a594d49733 100644
> --- a/include/linux/mount.h
> +++ b/include/linux/mount.h
> @@ -81,6 +81,7 @@ extern void mntput(struct vfsmount *mnt);
>  extern struct vfsmount *mntget(struct vfsmount *mnt);
>  extern struct vfsmount *mnt_clone_internal(struct path *path);
>  extern int __mnt_is_readonly(struct vfsmount *mnt);
> +extern bool mnt_may_suid(struct vfsmount *mnt);
>  
>  struct path;
>  extern struct vfsmount *clone_private_mount(struct path *path);
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 400aa224b491..6243aef5860e 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -448,7 +448,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
>  	if (!file_caps_enabled)
>  		return 0;
>  
> -	if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
> +	if (!mnt_may_suid(bprm->file->f_path.mnt))
>  		return 0;
>  	if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns))
>  		return 0;
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index d0cfaa9f19d0..a5b93df6553f 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2171,7 +2171,7 @@ static int check_nnp_nosuid(const struct linux_binprm *bprm,
>  			    const struct task_security_struct *new_tsec)
>  {
>  	int nnp = (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS);
> -	int nosuid = (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID);
> +	int nosuid = !mnt_may_suid(bprm->file->f_path.mnt);
>  	int rc;
>  
>  	if (!nnp && !nosuid)
> -- 
> 1.9.1

[PATCH 04/19] selinux: Add support for unprivileged mounts from user namespaces

[Seth Forshee]

Security labels from unprivileged mounts in user namespaces must
be ignored. Force superblocks from user namespaces whose labeling
behavior is to use xattrs to use mountpoint labeling instead.
For the mountpoint label, default to converting the current task
context into a form suitable for file objects, but also allow the
policy writer to specify a different label through policy
transition rules.

Pieced together from code snippets provided by Stephen Smalley.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: James Morris <james.l.morris@oracle.com>
---
 security/selinux/hooks.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index a5b93df6553f..5fedc36dd6b2 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -756,6 +756,28 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 			goto out;
 		}
 	}
+
+	/*
+	 * If this is a user namespace mount, no contexts are allowed
+	 * on the command line and security labels must be ignored.
+	 */
+	if (sb->s_user_ns != &init_user_ns) {
+		if (context_sid || fscontext_sid || rootcontext_sid ||
+		    defcontext_sid) {
+			rc = -EACCES;
+			goto out;
+		}
+		if (sbsec->behavior == SECURITY_FS_USE_XATTR) {
+			sbsec->behavior = SECURITY_FS_USE_MNTPOINT;
+			rc = security_transition_sid(current_sid(), current_sid(),
+						     SECCLASS_FILE, NULL,
+						     &sbsec->mntpoint_sid);
+			if (rc)
+				goto out;
+		}
+		goto out_set_opts;
+	}
+
 	/* sets the context of the superblock for the fs being mounted. */
 	if (fscontext_sid) {
 		rc = may_context_mount_sb_relabel(fscontext_sid, sbsec, cred);
@@ -824,6 +846,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 		sbsec->def_sid = defcontext_sid;
 	}
 
+out_set_opts:
 	rc = sb_finish_set_opts(sb);
 out:
 	mutex_unlock(&sbsec->lock);
-- 
1.9.1

[PATCH 05/19] userns: Replace in_userns with current_in_userns

[Seth Forshee]

All current callers of in_userns pass current_user_ns as the
first argument. Simplify by replacing in_userns with
current_in_userns which checks whether current_user_ns is in the
namespace supplied as an argument.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: James Morris <james.l.morris@oracle.com>
---
 fs/namespace.c                 | 2 +-
 include/linux/user_namespace.h | 6 ++----
 kernel/user_namespace.c        | 6 +++---
 security/commoncap.c           | 2 +-
 4 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 2101ce7b96ab..18fc58760aec 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3286,7 +3286,7 @@ bool mnt_may_suid(struct vfsmount *mnt)
 	 * in other namespaces.
 	 */
 	return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
-	       in_userns(current_user_ns(), mnt->mnt_sb->s_user_ns);
+	       current_in_userns(mnt->mnt_sb->s_user_ns);
 }
 
 static struct ns_common *mntns_get(struct task_struct *task)
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index a43faa727124..9217169c64cb 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -72,8 +72,7 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t,
 extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *);
 extern int proc_setgroups_show(struct seq_file *m, void *v);
 extern bool userns_may_setgroups(const struct user_namespace *ns);
-extern bool in_userns(const struct user_namespace *ns,
-		      const struct user_namespace *target_ns);
+extern bool current_in_userns(const struct user_namespace *target_ns);
 #else
 
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -103,8 +102,7 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns)
 	return true;
 }
 
-static inline bool in_userns(const struct user_namespace *ns,
-			     const struct user_namespace *target_ns)
+static inline bool current_in_userns(const struct user_namespace *target_ns)
 {
 	return true;
 }
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 69fbc377357b..5960edc7e644 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -949,10 +949,10 @@ bool userns_may_setgroups(const struct user_namespace *ns)
  * Returns true if @ns is the same namespace as or a descendant of
  * @target_ns.
  */
-bool in_userns(const struct user_namespace *ns,
-	       const struct user_namespace *target_ns)
+bool current_in_userns(const struct user_namespace *target_ns)
 {
-	for (; ns; ns = ns->parent) {
+	struct user_namespace *ns;
+	for (ns = current_user_ns(); ns; ns = ns->parent) {
 		if (ns == target_ns)
 			return true;
 	}
diff --git a/security/commoncap.c b/security/commoncap.c
index 6243aef5860e..2119421613f6 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -450,7 +450,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
 
 	if (!mnt_may_suid(bprm->file->f_path.mnt))
 		return 0;
-	if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns))
+	if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))
 		return 0;
 
 	rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
-- 
1.9.1

Re: [PATCH 05/19] userns: Replace in_userns with current_in_userns

[Serge E. Hallyn]

On Wed, Dec 02, 2015 at 09:40:05AM -0600, Seth Forshee wrote:
> All current callers of in_userns pass current_user_ns as the
> first argument. Simplify by replacing in_userns with
> current_in_userns which checks whether current_user_ns is in the
> namespace supplied as an argument.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> Acked-by: James Morris <james.l.morris@oracle.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/namespace.c                 | 2 +-
>  include/linux/user_namespace.h | 6 ++----
>  kernel/user_namespace.c        | 6 +++---
>  security/commoncap.c           | 2 +-
>  4 files changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 2101ce7b96ab..18fc58760aec 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -3286,7 +3286,7 @@ bool mnt_may_suid(struct vfsmount *mnt)
>  	 * in other namespaces.
>  	 */
>  	return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
> -	       in_userns(current_user_ns(), mnt->mnt_sb->s_user_ns);
> +	       current_in_userns(mnt->mnt_sb->s_user_ns);
>  }
>  
>  static struct ns_common *mntns_get(struct task_struct *task)
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index a43faa727124..9217169c64cb 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -72,8 +72,7 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t,
>  extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *);
>  extern int proc_setgroups_show(struct seq_file *m, void *v);
>  extern bool userns_may_setgroups(const struct user_namespace *ns);
> -extern bool in_userns(const struct user_namespace *ns,
> -		      const struct user_namespace *target_ns);
> +extern bool current_in_userns(const struct user_namespace *target_ns);
>  #else
>  
>  static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
> @@ -103,8 +102,7 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns)
>  	return true;
>  }
>  
> -static inline bool in_userns(const struct user_namespace *ns,
> -			     const struct user_namespace *target_ns)
> +static inline bool current_in_userns(const struct user_namespace *target_ns)
>  {
>  	return true;
>  }
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 69fbc377357b..5960edc7e644 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -949,10 +949,10 @@ bool userns_may_setgroups(const struct user_namespace *ns)
>   * Returns true if @ns is the same namespace as or a descendant of
>   * @target_ns.
>   */
> -bool in_userns(const struct user_namespace *ns,
> -	       const struct user_namespace *target_ns)
> +bool current_in_userns(const struct user_namespace *target_ns)
>  {
> -	for (; ns; ns = ns->parent) {
> +	struct user_namespace *ns;
> +	for (ns = current_user_ns(); ns; ns = ns->parent) {
>  		if (ns == target_ns)
>  			return true;
>  	}
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 6243aef5860e..2119421613f6 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -450,7 +450,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
>  
>  	if (!mnt_may_suid(bprm->file->f_path.mnt))
>  		return 0;
> -	if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns))
> +	if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))
>  		return 0;
>  
>  	rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
> -- 
> 1.9.1

[PATCH 06/19] Smack: Handle labels consistently in untrusted mounts

[Seth Forshee]

The SMACK64, SMACK64EXEC, and SMACK64MMAP labels are all handled
differently in untrusted mounts. This is confusing and
potentically problematic. Change this to handle them all the same
way that SMACK64 is currently handled; that is, read the label
from disk and check it at use time. For SMACK64 and SMACK64MMAP
access is denied if the label does not match smk_root. To be
consistent with suid, a SMACK64EXEC label which does not match
smk_root will still allow execution of the file but will not run
with the label supplied in the xattr.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
---
 security/smack/smack_lsm.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 16cac04214e2..0e555f64ded0 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -921,6 +921,7 @@ static int smack_bprm_set_creds(struct linux_binprm *bprm)
 	struct inode *inode = file_inode(bprm->file);
 	struct task_smack *bsp = bprm->cred->security;
 	struct inode_smack *isp;
+	struct superblock_smack *sbsp;
 	int rc;
 
 	if (bprm->cred_prepared)
@@ -930,6 +931,11 @@ static int smack_bprm_set_creds(struct linux_binprm *bprm)
 	if (isp->smk_task == NULL || isp->smk_task == bsp->smk_task)
 		return 0;
 
+	sbsp = inode->i_sb->s_security;
+	if ((sbsp->smk_flags & SMK_SB_UNTRUSTED) &&
+	    isp->smk_task != sbsp->smk_root)
+		return 0;
+
 	if (bprm->unsafe & (LSM_UNSAFE_PTRACE | LSM_UNSAFE_PTRACE_CAP)) {
 		struct task_struct *tracer;
 		rc = 0;
@@ -1733,6 +1739,7 @@ static int smack_mmap_file(struct file *file,
 	struct task_smack *tsp;
 	struct smack_known *okp;
 	struct inode_smack *isp;
+	struct superblock_smack *sbsp;
 	int may;
 	int mmay;
 	int tmay;
@@ -1744,6 +1751,10 @@ static int smack_mmap_file(struct file *file,
 	isp = file_inode(file)->i_security;
 	if (isp->smk_mmap == NULL)
 		return 0;
+	sbsp = file_inode(file)->i_sb->s_security;
+	if (sbsp->smk_flags & SMK_SB_UNTRUSTED &&
+	    isp->smk_mmap != sbsp->smk_root)
+		return -EACCES;
 	mkp = isp->smk_mmap;
 
 	tsp = current_security();
@@ -3532,16 +3543,14 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
 			if (rc >= 0)
 				transflag = SMK_INODE_TRANSMUTE;
 		}
-		if (!(sbsp->smk_flags & SMK_SB_UNTRUSTED)) {
-			/*
-			 * Don't let the exec or mmap label be "*" or "@".
-			 */
-			skp = smk_fetch(XATTR_NAME_SMACKEXEC, inode, dp);
-			if (IS_ERR(skp) || skp == &smack_known_star ||
-			    skp == &smack_known_web)
-				skp = NULL;
-			isp->smk_task = skp;
-		}
+		/*
+		 * Don't let the exec or mmap label be "*" or "@".
+		 */
+		skp = smk_fetch(XATTR_NAME_SMACKEXEC, inode, dp);
+		if (IS_ERR(skp) || skp == &smack_known_star ||
+		    skp == &smack_known_web)
+			skp = NULL;
+		isp->smk_task = skp;
 
 		skp = smk_fetch(XATTR_NAME_SMACKMMAP, inode, dp);
 		if (IS_ERR(skp) || skp == &smack_known_star ||
-- 
1.9.1

[PATCH 07/19] fs: Check for invalid i_uid in may_follow_link()

[Seth Forshee]

Filesystem uids which don't map into a user namespace may result
in inode->i_uid being INVALID_UID. A symlink and its parent
could have different owners in the filesystem can both get
mapped to INVALID_UID, which may result in following a symlink
when this would not have otherwise been permitted when protected
symlinks are enabled.

Add a new helper function, uid_valid_eq(), and use this to
validate that the ids in may_follow_link() are both equal and
valid. Also add an equivalent helper for gids, which is
currently unused.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/namei.c             |  2 +-
 include/linux/uidgid.h | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 288e8a74bf88..4ccafd391697 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -902,7 +902,7 @@ static inline int may_follow_link(struct nameidata *nd)
 		return 0;
 
 	/* Allowed if parent directory and link owner match. */
-	if (uid_eq(parent->i_uid, inode->i_uid))
+	if (uid_valid_eq(parent->i_uid, inode->i_uid))
 		return 0;
 
 	if (nd->flags & LOOKUP_RCU)
diff --git a/include/linux/uidgid.h b/include/linux/uidgid.h
index 03835522dfcb..e09529fe2668 100644
--- a/include/linux/uidgid.h
+++ b/include/linux/uidgid.h
@@ -117,6 +117,16 @@ static inline bool gid_valid(kgid_t gid)
 	return __kgid_val(gid) != (gid_t) -1;
 }
 
+static inline bool uid_valid_eq(kuid_t left, kuid_t right)
+{
+	return uid_eq(left, right) && uid_valid(left);
+}
+
+static inline bool gid_valid_eq(kgid_t left, kgid_t right)
+{
+	return gid_eq(left, right) && gid_valid(left);
+}
+
 #ifdef CONFIG_USER_NS
 
 extern kuid_t make_kuid(struct user_namespace *from, uid_t uid);
-- 
1.9.1

Re: [PATCH 07/19] fs: Check for invalid i_uid in may_follow_link()

[Serge E. Hallyn]

On Wed, Dec 02, 2015 at 09:40:07AM -0600, Seth Forshee wrote:
> Filesystem uids which don't map into a user namespace may result
> in inode->i_uid being INVALID_UID. A symlink and its parent
> could have different owners in the filesystem can both get
> mapped to INVALID_UID, which may result in following a symlink
> when this would not have otherwise been permitted when protected
> symlinks are enabled.
> 
> Add a new helper function, uid_valid_eq(), and use this to
> validate that the ids in may_follow_link() are both equal and
> valid. Also add an equivalent helper for gids, which is
> currently unused.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/namei.c             |  2 +-
>  include/linux/uidgid.h | 10 ++++++++++
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 288e8a74bf88..4ccafd391697 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -902,7 +902,7 @@ static inline int may_follow_link(struct nameidata *nd)
>  		return 0;
>  
>  	/* Allowed if parent directory and link owner match. */
> -	if (uid_eq(parent->i_uid, inode->i_uid))
> +	if (uid_valid_eq(parent->i_uid, inode->i_uid))
>  		return 0;
>  
>  	if (nd->flags & LOOKUP_RCU)
> diff --git a/include/linux/uidgid.h b/include/linux/uidgid.h
> index 03835522dfcb..e09529fe2668 100644
> --- a/include/linux/uidgid.h
> +++ b/include/linux/uidgid.h
> @@ -117,6 +117,16 @@ static inline bool gid_valid(kgid_t gid)
>  	return __kgid_val(gid) != (gid_t) -1;
>  }
>  
> +static inline bool uid_valid_eq(kuid_t left, kuid_t right)
> +{
> +	return uid_eq(left, right) && uid_valid(left);
> +}
> +
> +static inline bool gid_valid_eq(kgid_t left, kgid_t right)
> +{
> +	return gid_eq(left, right) && gid_valid(left);
> +}
> +
>  #ifdef CONFIG_USER_NS
>  
>  extern kuid_t make_kuid(struct user_namespace *from, uid_t uid);
> -- 
> 1.9.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

[PATCH 08/19] cred: Reject inodes with invalid ids in set_create_file_as()

[Seth Forshee]

Using INVALID_[UG]ID for the LSM file creation context doesn't
make sense, so return an error if the inode passed to
set_create_file_as() has an invalid id.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 kernel/cred.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/cred.c b/kernel/cred.c
index 71179a09c1d6..ff8606f77d90 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -689,6 +689,8 @@ EXPORT_SYMBOL(set_security_override_from_ctx);
  */
 int set_create_files_as(struct cred *new, struct inode *inode)
 {
+	if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
+		return -EINVAL;
 	new->fsuid = inode->i_uid;
 	new->fsgid = inode->i_gid;
 	return security_kernel_create_files_as(new, inode);
-- 
1.9.1

Re: [PATCH 08/19] cred: Reject inodes with invalid ids in set_create_file_as()

[Serge E. Hallyn]

On Wed, Dec 02, 2015 at 09:40:08AM -0600, Seth Forshee wrote:
> Using INVALID_[UG]ID for the LSM file creation context doesn't
> make sense, so return an error if the inode passed to
> set_create_file_as() has an invalid id.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  kernel/cred.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/cred.c b/kernel/cred.c
> index 71179a09c1d6..ff8606f77d90 100644
> --- a/kernel/cred.c
> +++ b/kernel/cred.c
> @@ -689,6 +689,8 @@ EXPORT_SYMBOL(set_security_override_from_ctx);
>   */
>  int set_create_files_as(struct cred *new, struct inode *inode)
>  {
> +	if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
> +		return -EINVAL;
>  	new->fsuid = inode->i_uid;
>  	new->fsgid = inode->i_gid;
>  	return security_kernel_create_files_as(new, inode);
> -- 
> 1.9.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

[PATCH 09/19] fs: Refuse uid/gid changes which don't map into s_user_ns

[Seth Forshee]

Add checks to inode_change_ok to verify that uid and gid changes
will map into the superblock's user namespace. If they do not
fail with -EOVERFLOW. This cannot be overriden with ATTR_FORCE.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/attr.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/attr.c b/fs/attr.c
index 6530ced19697..55b46e3aa888 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -42,6 +42,17 @@ int inode_change_ok(const struct inode *inode, struct iattr *attr)
 			return error;
 	}
 
+	/*
+	 * Verify that uid/gid changes are valid in the target namespace
+	 * of the superblock. This cannot be overriden using ATTR_FORCE.
+	 */
+	if (ia_valid & ATTR_UID &&
+	    from_kuid(inode->i_sb->s_user_ns, attr->ia_uid) == (uid_t)-1)
+		return -EOVERFLOW;
+	if (ia_valid & ATTR_GID &&
+	    from_kgid(inode->i_sb->s_user_ns, attr->ia_gid) == (gid_t)-1)
+		return -EOVERFLOW;
+
 	/* If force is set do it anyway. */
 	if (ia_valid & ATTR_FORCE)
 		return 0;
-- 
1.9.1

Re: [PATCH 09/19] fs: Refuse uid/gid changes which don't map into s_user_ns

[Serge E. Hallyn]

On Wed, Dec 02, 2015 at 09:40:09AM -0600, Seth Forshee wrote:
> Add checks to inode_change_ok to verify that uid and gid changes
> will map into the superblock's user namespace. If they do not
> fail with -EOVERFLOW. This cannot be overriden with ATTR_FORCE.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

...  although i could see root on the host being upset that it can't
assign a uid not valid in the mounter's ns.  But it does seem safer.

> ---
>  fs/attr.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/fs/attr.c b/fs/attr.c
> index 6530ced19697..55b46e3aa888 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -42,6 +42,17 @@ int inode_change_ok(const struct inode *inode, struct iattr *attr)
>  			return error;
>  	}
>  
> +	/*
> +	 * Verify that uid/gid changes are valid in the target namespace
> +	 * of the superblock. This cannot be overriden using ATTR_FORCE.
> +	 */
> +	if (ia_valid & ATTR_UID &&
> +	    from_kuid(inode->i_sb->s_user_ns, attr->ia_uid) == (uid_t)-1)
> +		return -EOVERFLOW;
> +	if (ia_valid & ATTR_GID &&
> +	    from_kgid(inode->i_sb->s_user_ns, attr->ia_gid) == (gid_t)-1)
> +		return -EOVERFLOW;
> +
>  	/* If force is set do it anyway. */
>  	if (ia_valid & ATTR_FORCE)
>  		return 0;
> -- 
> 1.9.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: [PATCH 09/19] fs: Refuse uid/gid changes which don't map into s_user_ns

[Seth Forshee]

On Fri, Dec 04, 2015 at 11:27:38AM -0600, Serge E. Hallyn wrote:
> On Wed, Dec 02, 2015 at 09:40:09AM -0600, Seth Forshee wrote:
> > Add checks to inode_change_ok to verify that uid and gid changes
> > will map into the superblock's user namespace. If they do not
> > fail with -EOVERFLOW. This cannot be overriden with ATTR_FORCE.
> > 
> > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> 
> Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
> 
> ...  although i could see root on the host being upset that it can't
> assign a uid not valid in the mounter's ns.  But it does seem safer.

That change wouldn't be representable in the backing store though, and
that could lead to unexpected behaviour. It's better to tell root that
we can't make the requested change, in my opinion.

Re: [PATCH 09/19] fs: Refuse uid/gid changes which don't map into s_user_ns

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> On Fri, Dec 04, 2015 at 11:27:38AM -0600, Serge E. Hallyn wrote:
> > On Wed, Dec 02, 2015 at 09:40:09AM -0600, Seth Forshee wrote:
> > > Add checks to inode_change_ok to verify that uid and gid changes
> > > will map into the superblock's user namespace. If they do not
> > > fail with -EOVERFLOW. This cannot be overriden with ATTR_FORCE.
> > > 
> > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > 
> > Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
> > 
> > ...  although i could see root on the host being upset that it can't
> > assign a uid not valid in the mounter's ns.  But it does seem safer.
> 
> That change wouldn't be representable in the backing store though, and
> that could lead to unexpected behaviour. It's better to tell root that
> we can't make the requested change, in my opinion.

Makes sense.  Thanks.

[PATCH 10/19] fs: Update posix_acl support to handle user namespace mounts

[Seth Forshee]

ids in on-disk ACLs should be converted to s_user_ns instead of
init_user_ns as is done now. This introduces the possibility for
id mappings to fail, and when this happens syscalls will return
EOVERFLOW.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/posix_acl.c                  | 67 ++++++++++++++++++++++++++---------------
 fs/xattr.c                      | 19 +++++++++---
 include/linux/posix_acl_xattr.h | 17 ++++++++---
 3 files changed, 70 insertions(+), 33 deletions(-)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 4adde1e2cbec..a29442eb4af8 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -595,59 +595,77 @@ EXPORT_SYMBOL_GPL(posix_acl_create);
 /*
  * Fix up the uids and gids in posix acl extended attributes in place.
  */
-static void posix_acl_fix_xattr_userns(
+static int posix_acl_fix_xattr_userns(
 	struct user_namespace *to, struct user_namespace *from,
 	void *value, size_t size)
 {
 	posix_acl_xattr_header *header = (posix_acl_xattr_header *)value;
 	posix_acl_xattr_entry *entry = (posix_acl_xattr_entry *)(header+1), *end;
 	int count;
-	kuid_t uid;
-	kgid_t gid;
+	kuid_t kuid;
+	uid_t uid;
+	kgid_t kgid;
+	gid_t gid;
 
 	if (!value)
-		return;
+		return 0;
 	if (size < sizeof(posix_acl_xattr_header))
-		return;
+		return 0;
 	if (header->a_version != cpu_to_le32(POSIX_ACL_XATTR_VERSION))
-		return;
+		return 0;
 
 	count = posix_acl_xattr_count(size);
 	if (count < 0)
-		return;
+		return 0;
 	if (count == 0)
-		return;
+		return 0;
 
 	for (end = entry + count; entry != end; entry++) {
 		switch(le16_to_cpu(entry->e_tag)) {
 		case ACL_USER:
-			uid = make_kuid(from, le32_to_cpu(entry->e_id));
-			entry->e_id = cpu_to_le32(from_kuid(to, uid));
+			kuid = make_kuid(from, le32_to_cpu(entry->e_id));
+			if (!uid_valid(kuid))
+				return -EOVERFLOW;
+			uid = from_kuid(to, kuid);
+			if (uid == (uid_t)-1)
+				return -EOVERFLOW;
+			entry->e_id = cpu_to_le32(uid);
 			break;
 		case ACL_GROUP:
-			gid = make_kgid(from, le32_to_cpu(entry->e_id));
-			entry->e_id = cpu_to_le32(from_kgid(to, gid));
+			kgid = make_kgid(from, le32_to_cpu(entry->e_id));
+			if (!gid_valid(kgid))
+				return -EOVERFLOW;
+			gid = from_kgid(to, kgid);
+			if (gid == (gid_t)-1)
+				return -EOVERFLOW;
+			entry->e_id = cpu_to_le32(gid);
 			break;
 		default:
 			break;
 		}
 	}
+
+	return 0;
 }
 
-void posix_acl_fix_xattr_from_user(void *value, size_t size)
+int
+posix_acl_fix_xattr_from_user(struct user_namespace *target_ns, void *value,
+			      size_t size)
 {
-	struct user_namespace *user_ns = current_user_ns();
-	if (user_ns == &init_user_ns)
-		return;
-	posix_acl_fix_xattr_userns(&init_user_ns, user_ns, value, size);
+	struct user_namespace *source_ns = current_user_ns();
+	if (source_ns == target_ns)
+		return 0;
+	return posix_acl_fix_xattr_userns(target_ns, source_ns, value, size);
 }
 
-void posix_acl_fix_xattr_to_user(void *value, size_t size)
+int
+posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+			    size_t size)
 {
-	struct user_namespace *user_ns = current_user_ns();
-	if (user_ns == &init_user_ns)
-		return;
-	posix_acl_fix_xattr_userns(user_ns, &init_user_ns, value, size);
+	struct user_namespace *target_ns = current_user_ns();
+	if (target_ns == source_ns)
+		return 0;
+	return posix_acl_fix_xattr_userns(target_ns, source_ns, value, size);
 }
 
 /*
@@ -782,7 +800,7 @@ posix_acl_xattr_get(const struct xattr_handler *handler,
 	if (acl == NULL)
 		return -ENODATA;
 
-	error = posix_acl_to_xattr(&init_user_ns, acl, value, size);
+	error = posix_acl_to_xattr(dentry->d_sb->s_user_ns, acl, value, size);
 	posix_acl_release(acl);
 
 	return error;
@@ -810,7 +828,8 @@ posix_acl_xattr_set(const struct xattr_handler *handler,
 		return -EPERM;
 
 	if (value) {
-		acl = posix_acl_from_xattr(&init_user_ns, value, size);
+		acl = posix_acl_from_xattr(dentry->d_sb->s_user_ns, value,
+					   size);
 		if (IS_ERR(acl))
 			return PTR_ERR(acl);
 
diff --git a/fs/xattr.c b/fs/xattr.c
index 9b932b95d74e..1268d8d5f74b 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -351,8 +351,12 @@ setxattr(struct dentry *d, const char __user *name, const void __user *value,
 			goto out;
 		}
 		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
-		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
-			posix_acl_fix_xattr_from_user(kvalue, size);
+		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) {
+			error = posix_acl_fix_xattr_from_user(d->d_sb->s_user_ns,
+							      kvalue, size);
+			if (error)
+				goto out;
+		}
 	}
 
 	error = vfs_setxattr(d, kname, kvalue, size, flags);
@@ -452,9 +456,14 @@ getxattr(struct dentry *d, const char __user *name, void __user *value,
 	error = vfs_getxattr(d, kname, kvalue, size);
 	if (error > 0) {
 		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
-		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
-			posix_acl_fix_xattr_to_user(kvalue, size);
-		if (size && copy_to_user(value, kvalue, error))
+		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) {
+			int ret;
+			ret = posix_acl_fix_xattr_to_user(d->d_sb->s_user_ns,
+							  kvalue, size);
+			if (ret)
+				error = ret;
+		}
+		if (error > 0 && size && copy_to_user(value, kvalue, error))
 			error = -EFAULT;
 	} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
 		/* The file system tried to returned a value bigger
diff --git a/include/linux/posix_acl_xattr.h b/include/linux/posix_acl_xattr.h
index 6f14ee295822..db63c57357b4 100644
--- a/include/linux/posix_acl_xattr.h
+++ b/include/linux/posix_acl_xattr.h
@@ -53,14 +53,23 @@ posix_acl_xattr_count(size_t size)
 }
 
 #ifdef CONFIG_FS_POSIX_ACL
-void posix_acl_fix_xattr_from_user(void *value, size_t size);
-void posix_acl_fix_xattr_to_user(void *value, size_t size);
+int posix_acl_fix_xattr_from_user(struct user_namespace *target_ns,
+				  void *value, size_t size);
+int posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+				size_t size);
 #else
-static inline void posix_acl_fix_xattr_from_user(void *value, size_t size)
+static inline int
+posix_acl_fix_xattr_from_user(struct user_namespace *target_ns, void *value,
+			      size_t size)
 {
+	return 0;
 }
-static inline void posix_acl_fix_xattr_to_user(void *value, size_t size)
+
+static inline int
+posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+			    size_t size)
 {
+	return 0;
 }
 #endif
 
-- 
1.9.1

Re: [PATCH 10/19] fs: Update posix_acl support to handle user namespace mounts

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> ids in on-disk ACLs should be converted to s_user_ns instead of
> init_user_ns as is done now. This introduces the possibility for
> id mappings to fail, and when this happens syscalls will return
> EOVERFLOW.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/posix_acl.c                  | 67 ++++++++++++++++++++++++++---------------
>  fs/xattr.c                      | 19 +++++++++---
>  include/linux/posix_acl_xattr.h | 17 ++++++++---
>  3 files changed, 70 insertions(+), 33 deletions(-)
> 
> diff --git a/fs/posix_acl.c b/fs/posix_acl.c
> index 4adde1e2cbec..a29442eb4af8 100644
> --- a/fs/posix_acl.c
> +++ b/fs/posix_acl.c
> @@ -595,59 +595,77 @@ EXPORT_SYMBOL_GPL(posix_acl_create);
>  /*
>   * Fix up the uids and gids in posix acl extended attributes in place.
>   */
> -static void posix_acl_fix_xattr_userns(
> +static int posix_acl_fix_xattr_userns(
>  	struct user_namespace *to, struct user_namespace *from,
>  	void *value, size_t size)
>  {
>  	posix_acl_xattr_header *header = (posix_acl_xattr_header *)value;
>  	posix_acl_xattr_entry *entry = (posix_acl_xattr_entry *)(header+1), *end;
>  	int count;
> -	kuid_t uid;
> -	kgid_t gid;
> +	kuid_t kuid;
> +	uid_t uid;
> +	kgid_t kgid;
> +	gid_t gid;
>  
>  	if (!value)
> -		return;
> +		return 0;
>  	if (size < sizeof(posix_acl_xattr_header))
> -		return;
> +		return 0;
>  	if (header->a_version != cpu_to_le32(POSIX_ACL_XATTR_VERSION))
> -		return;
> +		return 0;
>  
>  	count = posix_acl_xattr_count(size);
>  	if (count < 0)
> -		return;
> +		return 0;
>  	if (count == 0)
> -		return;
> +		return 0;
>  
>  	for (end = entry + count; entry != end; entry++) {
>  		switch(le16_to_cpu(entry->e_tag)) {
>  		case ACL_USER:
> -			uid = make_kuid(from, le32_to_cpu(entry->e_id));
> -			entry->e_id = cpu_to_le32(from_kuid(to, uid));
> +			kuid = make_kuid(from, le32_to_cpu(entry->e_id));
> +			if (!uid_valid(kuid))
> +				return -EOVERFLOW;
> +			uid = from_kuid(to, kuid);
> +			if (uid == (uid_t)-1)
> +				return -EOVERFLOW;
> +			entry->e_id = cpu_to_le32(uid);
>  			break;
>  		case ACL_GROUP:
> -			gid = make_kgid(from, le32_to_cpu(entry->e_id));
> -			entry->e_id = cpu_to_le32(from_kgid(to, gid));
> +			kgid = make_kgid(from, le32_to_cpu(entry->e_id));
> +			if (!gid_valid(kgid))
> +				return -EOVERFLOW;
> +			gid = from_kgid(to, kgid);
> +			if (gid == (gid_t)-1)
> +				return -EOVERFLOW;
> +			entry->e_id = cpu_to_le32(gid);
>  			break;
>  		default:
>  			break;
>  		}
>  	}
> +
> +	return 0;
>  }
>  
> -void posix_acl_fix_xattr_from_user(void *value, size_t size)
> +int
> +posix_acl_fix_xattr_from_user(struct user_namespace *target_ns, void *value,
> +			      size_t size)
>  {
> -	struct user_namespace *user_ns = current_user_ns();
> -	if (user_ns == &init_user_ns)
> -		return;
> -	posix_acl_fix_xattr_userns(&init_user_ns, user_ns, value, size);
> +	struct user_namespace *source_ns = current_user_ns();
> +	if (source_ns == target_ns)
> +		return 0;
> +	return posix_acl_fix_xattr_userns(target_ns, source_ns, value, size);
>  }
>  
> -void posix_acl_fix_xattr_to_user(void *value, size_t size)
> +int
> +posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
> +			    size_t size)
>  {
> -	struct user_namespace *user_ns = current_user_ns();
> -	if (user_ns == &init_user_ns)
> -		return;
> -	posix_acl_fix_xattr_userns(user_ns, &init_user_ns, value, size);
> +	struct user_namespace *target_ns = current_user_ns();
> +	if (target_ns == source_ns)
> +		return 0;
> +	return posix_acl_fix_xattr_userns(target_ns, source_ns, value, size);
>  }
>  
>  /*
> @@ -782,7 +800,7 @@ posix_acl_xattr_get(const struct xattr_handler *handler,
>  	if (acl == NULL)
>  		return -ENODATA;
>  
> -	error = posix_acl_to_xattr(&init_user_ns, acl, value, size);
> +	error = posix_acl_to_xattr(dentry->d_sb->s_user_ns, acl, value, size);
>  	posix_acl_release(acl);
>  
>  	return error;
> @@ -810,7 +828,8 @@ posix_acl_xattr_set(const struct xattr_handler *handler,
>  		return -EPERM;
>  
>  	if (value) {
> -		acl = posix_acl_from_xattr(&init_user_ns, value, size);
> +		acl = posix_acl_from_xattr(dentry->d_sb->s_user_ns, value,
> +					   size);
>  		if (IS_ERR(acl))
>  			return PTR_ERR(acl);
>  
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 9b932b95d74e..1268d8d5f74b 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -351,8 +351,12 @@ setxattr(struct dentry *d, const char __user *name, const void __user *value,
>  			goto out;
>  		}
>  		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
> -		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
> -			posix_acl_fix_xattr_from_user(kvalue, size);
> +		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) {
> +			error = posix_acl_fix_xattr_from_user(d->d_sb->s_user_ns,
> +							      kvalue, size);
> +			if (error)
> +				goto out;
> +		}
>  	}
>  
>  	error = vfs_setxattr(d, kname, kvalue, size, flags);
> @@ -452,9 +456,14 @@ getxattr(struct dentry *d, const char __user *name, void __user *value,
>  	error = vfs_getxattr(d, kname, kvalue, size);
>  	if (error > 0) {
>  		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
> -		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
> -			posix_acl_fix_xattr_to_user(kvalue, size);
> -		if (size && copy_to_user(value, kvalue, error))
> +		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) {
> +			int ret;
> +			ret = posix_acl_fix_xattr_to_user(d->d_sb->s_user_ns,
> +							  kvalue, size);
> +			if (ret)
> +				error = ret;
> +		}
> +		if (error > 0 && size && copy_to_user(value, kvalue, error))
>  			error = -EFAULT;
>  	} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
>  		/* The file system tried to returned a value bigger
> diff --git a/include/linux/posix_acl_xattr.h b/include/linux/posix_acl_xattr.h
> index 6f14ee295822..db63c57357b4 100644
> --- a/include/linux/posix_acl_xattr.h
> +++ b/include/linux/posix_acl_xattr.h
> @@ -53,14 +53,23 @@ posix_acl_xattr_count(size_t size)
>  }
>  
>  #ifdef CONFIG_FS_POSIX_ACL
> -void posix_acl_fix_xattr_from_user(void *value, size_t size);
> -void posix_acl_fix_xattr_to_user(void *value, size_t size);
> +int posix_acl_fix_xattr_from_user(struct user_namespace *target_ns,
> +				  void *value, size_t size);
> +int posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
> +				size_t size);
>  #else
> -static inline void posix_acl_fix_xattr_from_user(void *value, size_t size)
> +static inline int
> +posix_acl_fix_xattr_from_user(struct user_namespace *target_ns, void *value,
> +			      size_t size)
>  {
> +	return 0;
>  }
> -static inline void posix_acl_fix_xattr_to_user(void *value, size_t size)
> +
> +static inline int
> +posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
> +			    size_t size)
>  {
> +	return 0;
>  }
>  #endif
>  
> -- 
> 1.9.1
> 
> --
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[PATCH 11/19] fs: Ensure the mounter of a filesystem is privileged towards its inodes

[Seth Forshee]

The mounter of a filesystem should be privileged towards the
inodes of that filesystem. Extend the checks in
inode_owner_or_capable() and capable_wrt_inode_uidgid() to
permit access by users priviliged in the user namespace of the
inode's superblock.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/inode.c          |  3 +++
 kernel/capability.c | 13 +++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 1be5f9003eb3..01c036fe1950 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1962,6 +1962,9 @@ bool inode_owner_or_capable(const struct inode *inode)
 	ns = current_user_ns();
 	if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
 		return true;
+
+	if (ns_capable(inode->i_sb->s_user_ns, CAP_FOWNER))
+		return true;
 	return false;
 }
 EXPORT_SYMBOL(inode_owner_or_capable);
diff --git a/kernel/capability.c b/kernel/capability.c
index 45432b54d5c6..5137a38a5670 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -437,13 +437,18 @@ EXPORT_SYMBOL(file_ns_capable);
  *
  * Return true if the current task has the given capability targeted at
  * its own user namespace and that the given inode's uid and gid are
- * mapped into the current user namespace.
+ * mapped into the current user namespace, or if the current task has
+ * the capability towards the user namespace of the inode's superblock.
  */
 bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 {
-	struct user_namespace *ns = current_user_ns();
+	struct user_namespace *ns;
 
-	return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
-		kgid_has_mapping(ns, inode->i_gid);
+	ns = current_user_ns();
+	if (ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
+	    kgid_has_mapping(ns, inode->i_gid))
+		return true;
+
+	return ns_capable(inode->i_sb->s_user_ns, cap);
 }
 EXPORT_SYMBOL(capable_wrt_inode_uidgid);
-- 
1.9.1

Re: [PATCH 11/19] fs: Ensure the mounter of a filesystem is privileged towards its inodes

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> The mounter of a filesystem should be privileged towards the
> inodes of that filesystem. Extend the checks in
> inode_owner_or_capable() and capable_wrt_inode_uidgid() to
> permit access by users priviliged in the user namespace of the
> inode's superblock.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/inode.c          |  3 +++
>  kernel/capability.c | 13 +++++++++----
>  2 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 1be5f9003eb3..01c036fe1950 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1962,6 +1962,9 @@ bool inode_owner_or_capable(const struct inode *inode)
>  	ns = current_user_ns();
>  	if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
>  		return true;
> +
> +	if (ns_capable(inode->i_sb->s_user_ns, CAP_FOWNER))
> +		return true;
>  	return false;
>  }
>  EXPORT_SYMBOL(inode_owner_or_capable);
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 45432b54d5c6..5137a38a5670 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -437,13 +437,18 @@ EXPORT_SYMBOL(file_ns_capable);
>   *
>   * Return true if the current task has the given capability targeted at
>   * its own user namespace and that the given inode's uid and gid are
> - * mapped into the current user namespace.
> + * mapped into the current user namespace, or if the current task has
> + * the capability towards the user namespace of the inode's superblock.
>   */
>  bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
>  {
> -	struct user_namespace *ns = current_user_ns();
> +	struct user_namespace *ns;
>  
> -	return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
> -		kgid_has_mapping(ns, inode->i_gid);
> +	ns = current_user_ns();
> +	if (ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
> +	    kgid_has_mapping(ns, inode->i_gid))
> +		return true;
> +
> +	return ns_capable(inode->i_sb->s_user_ns, cap);
>  }
>  EXPORT_SYMBOL(capable_wrt_inode_uidgid);
> -- 
> 1.9.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

[PATCH 12/19] fs: Don't remove suid for CAP_FSETID in s_user_ns

[Seth Forshee]

Expand the check in should_remove_suid() to keep privileges for
CAP_FSETID in s_user_ns rather than init_user_ns.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 01c036fe1950..3e7c74da9304 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1684,7 +1684,8 @@ int should_remove_suid(struct dentry *dentry)
 	if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
 		kill |= ATTR_KILL_SGID;
 
-	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
+	if (unlikely(kill && !ns_capable(dentry->d_sb->s_user_ns, CAP_FSETID) &&
+		     S_ISREG(mode)))
 		return kill;
 
 	return 0;
-- 
1.9.1

Re: [PATCH 12/19] fs: Don't remove suid for CAP_FSETID in s_user_ns

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> Expand the check in should_remove_suid() to keep privileges for
> CAP_FSETID in s_user_ns rather than init_user_ns.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/inode.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 01c036fe1950..3e7c74da9304 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1684,7 +1684,8 @@ int should_remove_suid(struct dentry *dentry)
>  	if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
>  		kill |= ATTR_KILL_SGID;
>  
> -	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
> +	if (unlikely(kill && !ns_capable(dentry->d_sb->s_user_ns, CAP_FSETID) &&
> +		     S_ISREG(mode)))
>  		return kill;
>  
>  	return 0;
> -- 
> 1.9.1
> 
> --
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> the body of a message to majordomo@vger.kernel.org
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> Please read the FAQ at  http://www.tux.org/lkml/

[PATCH 13/19] fs: Allow superblock owner to access do_remount_sb()

[Seth Forshee]

Superblock level remounts are currently restricted to global
CAP_SYS_ADMIN, as is the path for changing the root mount to
read only on umount. Loosen both of these permission checks to
also allow CAP_SYS_ADMIN in any namespace which is privileged
towards the userns which originally mounted the filesystem.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/namespace.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 18fc58760aec..b00a765895e7 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1510,7 +1510,7 @@ static int do_umount(struct mount *mnt, int flags)
 		 * Special case for "unmounting" root ...
 		 * we just try to remount it readonly.
 		 */
-		if (!capable(CAP_SYS_ADMIN))
+		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
 			return -EPERM;
 		down_write(&sb->s_umount);
 		if (!(sb->s_flags & MS_RDONLY))
@@ -2199,7 +2199,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
 	down_write(&sb->s_umount);
 	if (flags & MS_BIND)
 		err = change_mount_flags(path->mnt, flags);
-	else if (!capable(CAP_SYS_ADMIN))
+	else if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
 		err = -EPERM;
 	else
 		err = do_remount_sb(sb, flags, data, 0);
-- 
1.9.1

Re: [PATCH 13/19] fs: Allow superblock owner to access do_remount_sb()

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> Superblock level remounts are currently restricted to global
> CAP_SYS_ADMIN, as is the path for changing the root mount to
> read only on umount. Loosen both of these permission checks to
> also allow CAP_SYS_ADMIN in any namespace which is privileged
> towards the userns which originally mounted the filesystem.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

>  fs/namespace.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 18fc58760aec..b00a765895e7 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -1510,7 +1510,7 @@ static int do_umount(struct mount *mnt, int flags)
>  		 * Special case for "unmounting" root ...
>  		 * we just try to remount it readonly.
>  		 */
> -		if (!capable(CAP_SYS_ADMIN))
> +		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
>  			return -EPERM;
>  		down_write(&sb->s_umount);
>  		if (!(sb->s_flags & MS_RDONLY))
> @@ -2199,7 +2199,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
>  	down_write(&sb->s_umount);
>  	if (flags & MS_BIND)
>  		err = change_mount_flags(path->mnt, flags);
> -	else if (!capable(CAP_SYS_ADMIN))
> +	else if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
>  		err = -EPERM;
>  	else
>  		err = do_remount_sb(sb, flags, data, 0);
> -- 
> 1.9.1
> 
> --
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[PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Seth Forshee]

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ioctl.c b/fs/ioctl.c
index 5d01d2638ca5..45c371bed7ee 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -55,7 +55,7 @@ static int ioctl_fibmap(struct file *filp, int __user *p)
 	/* do we support this mess? */
 	if (!mapping->a_ops->bmap)
 		return -EINVAL;
-	if (!capable(CAP_SYS_RAWIO))
+	if (!ns_capable(filp->f_inode->i_sb->s_user_ns, CAP_SYS_RAWIO))
 		return -EPERM;
 	res = get_user(block, p);
 	if (res)
-- 
1.9.1

Re: [PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 5d01d2638ca5..45c371bed7ee 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -55,7 +55,7 @@ static int ioctl_fibmap(struct file *filp, int __user *p)
>  	/* do we support this mess? */
>  	if (!mapping->a_ops->bmap)
>  		return -EINVAL;
> -	if (!capable(CAP_SYS_RAWIO))
> +	if (!ns_capable(filp->f_inode->i_sb->s_user_ns, CAP_SYS_RAWIO))
>  		return -EPERM;
>  	res = get_user(block, p);
>  	if (res)
> -- 
> 1.9.1
> 
> --
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Re: [PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Theodore Ts'o]

The fact that we need CAP_SYS_RAIO for FIBMAP is pretty silly, given
that FIEMAP does not require privileges --- and in fact the preferred
interface.  Why not just simply drop the requirement for privileges
for FIBMAP?

(Seth, Serge, this isn't a real objection to your patch; but the fact
that FIBMAP requires root has always been a bit silly, and this would
be a great opportunity to simplify things a bit.)

						- Ted
						

On Fri, Dec 04, 2015 at 01:11:43PM -0600, Serge E. Hallyn wrote:
> Quoting Seth Forshee (seth.forshee@canonical.com):
> > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> 
> Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
> 
> > ---
> >  fs/ioctl.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/ioctl.c b/fs/ioctl.c
> > index 5d01d2638ca5..45c371bed7ee 100644
> > --- a/fs/ioctl.c
> > +++ b/fs/ioctl.c
> > @@ -55,7 +55,7 @@ static int ioctl_fibmap(struct file *filp, int __user *p)
> >  	/* do we support this mess? */
> >  	if (!mapping->a_ops->bmap)
> >  		return -EINVAL;
> > -	if (!capable(CAP_SYS_RAWIO))
> > +	if (!ns_capable(filp->f_inode->i_sb->s_user_ns, CAP_SYS_RAWIO))
> >  		return -EPERM;
> >  	res = get_user(block, p);
> >  	if (res)
> > -- 
> > 1.9.1
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> --
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Re: [PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Serge E. Hallyn]

Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611
a little while ago :)  The same question was asked 16 years ago.  Apparently
the answer then was that it was easier than fixing the code.

Quoting Theodore Ts'o (tytso@mit.edu):
> The fact that we need CAP_SYS_RAIO for FIBMAP is pretty silly, given
> that FIEMAP does not require privileges --- and in fact the preferred
> interface.  Why not just simply drop the requirement for privileges
> for FIBMAP?
> 
> (Seth, Serge, this isn't a real objection to your patch; but the fact
> that FIBMAP requires root has always been a bit silly, and this would
> be a great opportunity to simplify things a bit.)
> 
> 						- Ted
> 						
> 
> On Fri, Dec 04, 2015 at 01:11:43PM -0600, Serge E. Hallyn wrote:
> > Quoting Seth Forshee (seth.forshee@canonical.com):
> > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > 
> > Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
> > 
> > > ---
> > >  fs/ioctl.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/ioctl.c b/fs/ioctl.c
> > > index 5d01d2638ca5..45c371bed7ee 100644
> > > --- a/fs/ioctl.c
> > > +++ b/fs/ioctl.c
> > > @@ -55,7 +55,7 @@ static int ioctl_fibmap(struct file *filp, int __user *p)
> > >  	/* do we support this mess? */
> > >  	if (!mapping->a_ops->bmap)
> > >  		return -EINVAL;
> > > -	if (!capable(CAP_SYS_RAWIO))
> > > +	if (!ns_capable(filp->f_inode->i_sb->s_user_ns, CAP_SYS_RAWIO))
> > >  		return -EPERM;
> > >  	res = get_user(block, p);
> > >  	if (res)
> > > -- 
> > > 1.9.1
> > > 
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > Please read the FAQ at  http://www.tux.org/lkml/
> > --
> > 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 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Seth Forshee]

On Fri, Dec 04, 2015 at 02:07:36PM -0600, Serge E. Hallyn wrote:
> Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611
> a little while ago :)  The same question was asked 16 years ago.  Apparently
> the answer then was that it was easier than fixing the code.

So it seems then that either it still isn't safe and so unprivileged
users shouldn't be allowed to do it at all, or else it's safe and we
should drop the requirement completely. I can't say which is right,
unfortunately.

> 
> Quoting Theodore Ts'o (tytso@mit.edu):
> > The fact that we need CAP_SYS_RAIO for FIBMAP is pretty silly, given
> > that FIEMAP does not require privileges --- and in fact the preferred
> > interface.  Why not just simply drop the requirement for privileges
> > for FIBMAP?
> > 
> > (Seth, Serge, this isn't a real objection to your patch; but the fact
> > that FIBMAP requires root has always been a bit silly, and this would
> > be a great opportunity to simplify things a bit.)
> > 
> > 						- Ted
> > 						
> > 
> > On Fri, Dec 04, 2015 at 01:11:43PM -0600, Serge E. Hallyn wrote:
> > > Quoting Seth Forshee (seth.forshee@canonical.com):
> > > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > > 
> > > Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
> > > 
> > > > ---
> > > >  fs/ioctl.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/fs/ioctl.c b/fs/ioctl.c
> > > > index 5d01d2638ca5..45c371bed7ee 100644
> > > > --- a/fs/ioctl.c
> > > > +++ b/fs/ioctl.c
> > > > @@ -55,7 +55,7 @@ static int ioctl_fibmap(struct file *filp, int __user *p)
> > > >  	/* do we support this mess? */
> > > >  	if (!mapping->a_ops->bmap)
> > > >  		return -EINVAL;
> > > > -	if (!capable(CAP_SYS_RAWIO))
> > > > +	if (!ns_capable(filp->f_inode->i_sb->s_user_ns, CAP_SYS_RAWIO))
> > > >  		return -EPERM;
> > > >  	res = get_user(block, p);
> > > >  	if (res)
> > > > -- 
> > > > 1.9.1
> > > > 
> > > > --
> > > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > > > the body of a message to majordomo@vger.kernel.org
> > > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > > Please read the FAQ at  http://www.tux.org/lkml/
> > > --
> > > 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 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Theodore Ts'o]

On Fri, Dec 04, 2015 at 02:45:32PM -0600, Seth Forshee wrote:
> On Fri, Dec 04, 2015 at 02:07:36PM -0600, Serge E. Hallyn wrote:
> > Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611
> > a little while ago :)  The same question was asked 16 years ago.  Apparently
> > the answer then was that it was easier than fixing the code.
> 
> So it seems then that either it still isn't safe and so unprivileged
> users shouldn't be allowed to do it at all, or else it's safe and we
> should drop the requirement completely. I can't say which is right,
> unfortunately.

It may not have been safe 16 years agoo, but giving invalid arguments
to FIBMAP is safe for ext4 and ext2.  This is the sort of thing that
tools like trinity should and does test for, so I think it should be
fine to remove the root check for FIBMAP.

							- Ted

Re: [PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Serge E. Hallyn]

On Fri, Dec 04, 2015 at 06:11:52PM -0500, Theodore Ts'o wrote:
> On Fri, Dec 04, 2015 at 02:45:32PM -0600, Seth Forshee wrote:
> > On Fri, Dec 04, 2015 at 02:07:36PM -0600, Serge E. Hallyn wrote:
> > > Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611
> > > a little while ago :)  The same question was asked 16 years ago.  Apparently
> > > the answer then was that it was easier than fixing the code.
> > 
> > So it seems then that either it still isn't safe and so unprivileged
> > users shouldn't be allowed to do it at all, or else it's safe and we
> > should drop the requirement completely. I can't say which is right,
> > unfortunately.
> 
> It may not have been safe 16 years agoo, but giving invalid arguments
> to FIBMAP is safe for ext4 and ext2.  This is the sort of thing that
> tools like trinity should and does test for, so I think it should be
> fine to remove the root check for FIBMAP.

Seth, can I tempt you into sending a standalone patch to remove that? :)

-serge

Re: [PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Seth Forshee]

On Fri, Dec 04, 2015 at 05:43:49PM -0600, Serge E. Hallyn wrote:
> On Fri, Dec 04, 2015 at 06:11:52PM -0500, Theodore Ts'o wrote:
> > On Fri, Dec 04, 2015 at 02:45:32PM -0600, Seth Forshee wrote:
> > > On Fri, Dec 04, 2015 at 02:07:36PM -0600, Serge E. Hallyn wrote:
> > > > Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611
> > > > a little while ago :)  The same question was asked 16 years ago.  Apparently
> > > > the answer then was that it was easier than fixing the code.
> > > 
> > > So it seems then that either it still isn't safe and so unprivileged
> > > users shouldn't be allowed to do it at all, or else it's safe and we
> > > should drop the requirement completely. I can't say which is right,
> > > unfortunately.
> > 
> > It may not have been safe 16 years agoo, but giving invalid arguments
> > to FIBMAP is safe for ext4 and ext2.  This is the sort of thing that
> > tools like trinity should and does test for, so I think it should be
> > fine to remove the root check for FIBMAP.
> 
> Seth, can I tempt you into sending a standalone patch to remove that? :)

Patch sent. I'll drop this patch in v2.

Re: [PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user_ns

[Andreas Dilger]

[-- Attachment #1: Type: text/plain, Size: 1531 bytes --]


> On Dec 4, 2015, at 4:11 PM, Theodore Ts'o <tytso@mit.edu> wrote:
> 
> On Fri, Dec 04, 2015 at 02:45:32PM -0600, Seth Forshee wrote:
>> On Fri, Dec 04, 2015 at 02:07:36PM -0600, Serge E. Hallyn wrote:
>>> Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611
>>> a little while ago :)  The same question was asked 16 years ago.  Apparently
>>> the answer then was that it was easier than fixing the code.
>> 
>> So it seems then that either it still isn't safe and so unprivileged
>> users shouldn't be allowed to do it at all, or else it's safe and we
>> should drop the requirement completely. I can't say which is right,
>> unfortunately.
> 
> It may not have been safe 16 years agoo, but giving invalid arguments
> to FIBMAP is safe for ext4 and ext2.  This is the sort of thing that
> tools like trinity should and does test for, so I think it should be
> fine to remove the root check for FIBMAP.

You can use FIEMAP on regular files and directories without special permission:

$ filefrag -v /etc
Filesystem type is: ef53
File size of /etc is 12288 (3 blocks of 4096 bytes)
 ext:     logical_offset:        physical_offset: length:   expected: flags:
   0:        0..       0:    8396832..   8396832:      1:
   1:        1..       2:    8397051..   8397052:      2:    8396833: last,eof
/etc: 2 extents found


FIEMAP also has the benefit that you don't need to call it millions of times
for large files, like is needed for FIBMAP.

Cheers, Andreas






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[PATCH 15/19] capabilities: Allow privileged user in s_user_ns to set file caps

[Seth Forshee]

A privileged user in a super block's s_user_ns is privileged
towards that file system and thus should be allowed to set file
capabilities. The file capabilities will not be trusted outside
of s_user_ns, so an unprivileged user cannot use this to gain
privileges in a user namespace where they are not already
privileged.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 security/commoncap.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/security/commoncap.c b/security/commoncap.c
index 2119421613f6..d6c80c19c449 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -653,15 +653,17 @@ int cap_bprm_secureexec(struct linux_binprm *bprm)
 int cap_inode_setxattr(struct dentry *dentry, const char *name,
 		       const void *value, size_t size, int flags)
 {
+	struct user_namespace *user_ns = dentry->d_sb->s_user_ns;
+
 	if (!strcmp(name, XATTR_NAME_CAPS)) {
-		if (!capable(CAP_SETFCAP))
+		if (!ns_capable(user_ns, CAP_SETFCAP))
 			return -EPERM;
 		return 0;
 	}
 
 	if (!strncmp(name, XATTR_SECURITY_PREFIX,
 		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
-	    !capable(CAP_SYS_ADMIN))
+	    !ns_capable(user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
 	return 0;
 }
@@ -679,15 +681,17 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name,
  */
 int cap_inode_removexattr(struct dentry *dentry, const char *name)
 {
+	struct user_namespace *user_ns = dentry->d_sb->s_user_ns;
+
 	if (!strcmp(name, XATTR_NAME_CAPS)) {
-		if (!capable(CAP_SETFCAP))
+		if (!ns_capable(user_ns, CAP_SETFCAP))
 			return -EPERM;
 		return 0;
 	}
 
 	if (!strncmp(name, XATTR_SECURITY_PREFIX,
 		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
-	    !capable(CAP_SYS_ADMIN))
+	    !ns_capable(user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
 	return 0;
 }
-- 
1.9.1

Re: [PATCH 15/19] capabilities: Allow privileged user in s_user_ns to set file caps

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> A privileged user in a super block's s_user_ns is privileged
> towards that file system and thus should be allowed to set file
> capabilities. The file capabilities will not be trusted outside
> of s_user_ns, so an unprivileged user cannot use this to gain
> privileges in a user namespace where they are not already
> privileged.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> ---
>  security/commoncap.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 2119421613f6..d6c80c19c449 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -653,15 +653,17 @@ int cap_bprm_secureexec(struct linux_binprm *bprm)
>  int cap_inode_setxattr(struct dentry *dentry, const char *name,
>  		       const void *value, size_t size, int flags)
>  {
> +	struct user_namespace *user_ns = dentry->d_sb->s_user_ns;
> +
>  	if (!strcmp(name, XATTR_NAME_CAPS)) {
> -		if (!capable(CAP_SETFCAP))
> +		if (!ns_capable(user_ns, CAP_SETFCAP))
>  			return -EPERM;

This, for file capabilities, is fine,

>  		return 0;
>  	}
>  
>  	if (!strncmp(name, XATTR_SECURITY_PREFIX,
>  		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
> -	    !capable(CAP_SYS_ADMIN))
> +	    !ns_capable(user_ns, CAP_SYS_ADMIN))

but this is for all other security.*.

It's probably still ok, but let's think about it a sec.  MAC like
selinux or smack should be orthogonal to DAC.  Capabilities are the
same in essence, but the reason they can be treated differently here
is because capabilties are in fact targated at a user namespace.
Apparmor namespaces, for instance, are completely orthogonal to user
namespaces, as are contexts in selinux.

Now, if smack or selinux xattrs are being set then those modules
should be gating these writes.  Booting a kernel without those
modules should be a challenge for an untrusted user.  But such a
situation could be exploited opportunistically if it were to happen.

The problem with simply not changing this here is that if selinux
or smack authorizes the xattr write, then commoncap shouldn't be
denying it.

I get the feeling we need cooperation among the modules (i.e. "if
the write is to 'security.$lsm' and $lsm is not loaded, then require
capable(CAP_SYS_ADMIN), else just allow)  But that's not how things are
structured right now.

Maybe security.ko could grow central logic to 'assign' security.*
capabilities to specific lsms and gate writes to those if $lsm is not
loaded.

Does anything break if the second hunk in each fn in this patch is
not applied?


>  		return -EPERM;
>  	return 0;
>  }
> @@ -679,15 +681,17 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name,
>   */
>  int cap_inode_removexattr(struct dentry *dentry, const char *name)
>  {
> +	struct user_namespace *user_ns = dentry->d_sb->s_user_ns;
> +
>  	if (!strcmp(name, XATTR_NAME_CAPS)) {
> -		if (!capable(CAP_SETFCAP))
> +		if (!ns_capable(user_ns, CAP_SETFCAP))
>  			return -EPERM;
>  		return 0;
>  	}
>  
>  	if (!strncmp(name, XATTR_SECURITY_PREFIX,
>  		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
> -	    !capable(CAP_SYS_ADMIN))
> +	    !ns_capable(user_ns, CAP_SYS_ADMIN))
>  		return -EPERM;
>  	return 0;
>  }
> -- 
> 1.9.1

Re: [PATCH 15/19] capabilities: Allow privileged user in s_user_ns to set file caps

[Seth Forshee]

On Fri, Dec 04, 2015 at 01:42:06PM -0600, Serge E. Hallyn wrote:
> Quoting Seth Forshee (seth.forshee@canonical.com):
> > A privileged user in a super block's s_user_ns is privileged
> > towards that file system and thus should be allowed to set file
> > capabilities. The file capabilities will not be trusted outside
> > of s_user_ns, so an unprivileged user cannot use this to gain
> > privileges in a user namespace where they are not already
> > privileged.
> > 
> > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > ---
> >  security/commoncap.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/security/commoncap.c b/security/commoncap.c
> > index 2119421613f6..d6c80c19c449 100644
> > --- a/security/commoncap.c
> > +++ b/security/commoncap.c
> > @@ -653,15 +653,17 @@ int cap_bprm_secureexec(struct linux_binprm *bprm)
> >  int cap_inode_setxattr(struct dentry *dentry, const char *name,
> >  		       const void *value, size_t size, int flags)
> >  {
> > +	struct user_namespace *user_ns = dentry->d_sb->s_user_ns;
> > +
> >  	if (!strcmp(name, XATTR_NAME_CAPS)) {
> > -		if (!capable(CAP_SETFCAP))
> > +		if (!ns_capable(user_ns, CAP_SETFCAP))
> >  			return -EPERM;
> 
> This, for file capabilities, is fine,
> 
> >  		return 0;
> >  	}
> >  
> >  	if (!strncmp(name, XATTR_SECURITY_PREFIX,
> >  		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
> > -	    !capable(CAP_SYS_ADMIN))
> > +	    !ns_capable(user_ns, CAP_SYS_ADMIN))
> 
> but this is for all other security.*.
> 
> It's probably still ok, but let's think about it a sec.  MAC like
> selinux or smack should be orthogonal to DAC.  Capabilities are the
> same in essence, but the reason they can be treated differently here
> is because capabilties are in fact targated at a user namespace.
> Apparmor namespaces, for instance, are completely orthogonal to user
> namespaces, as are contexts in selinux.
> 
> Now, if smack or selinux xattrs are being set then those modules
> should be gating these writes.  Booting a kernel without those
> modules should be a challenge for an untrusted user.  But such a
> situation could be exploited opportunistically if it were to happen.
> 
> The problem with simply not changing this here is that if selinux
> or smack authorizes the xattr write, then commoncap shouldn't be
> denying it.

This is partly the logic behind the change, the other part being that
the user could already insert the xattrs directly into the backing store
so the LSMs must be prepared not to trust them in any case. But the
commit message doesn't explain that, my mistake. And it's a question
worth revisiting.

> I get the feeling we need cooperation among the modules (i.e. "if
> the write is to 'security.$lsm' and $lsm is not loaded, then require
> capable(CAP_SYS_ADMIN), else just allow)  But that's not how things are
> structured right now.
> 
> Maybe security.ko could grow central logic to 'assign' security.*
> capabilities to specific lsms and gate writes to those if $lsm is not
> loaded.

I don't see any meaningful difference between this case and the case of
inserting them into the backing store before mounting. We can't do
anything to prevent the latter, so LSMs just have to be aware of
unprivileged mounts and handle them with care. Previous patches do this
for SELinux and Smack by adopting a policy that doesn't respect security
labels on disk for these mounts. So I don't think that refusing to set
security.* xattrs for an LSM that isn't loaded really accomplishes
anything.

Then there's the case of setting xattrs for an LSM that is currently
loaded. I think that SELinux and Smack are both going to refuse these
writes, Smack rather directly by seeing that the user lacks global
CAP_MAC_ADMIN and SELinux by virtue of the fact that the previous patch
in this series applies mountpoint labeling to these mounts. As far as I
can tell the other LSMs don't take security policy from xattrs.

So, as far as I can tell, removing the check doesn't create any
vulnerabilities.

But that's not to say it's the right thing to do. After reconsidering
it, I'm inclined to be more conservative and to keep requiring
capable(CAP_SYS_ADMIN) until such time as there's a use case for
allowing a user privileged only in s_user_ns to write these xattrs.

> Does anything break if the second hunk in each fn in this patch is
> not applied?

Not that I'm aware of, no.

Seth

Re: [PATCH 15/19] capabilities: Allow privileged user in s_user_ns to set file caps

[Serge E. Hallyn]

On Fri, Dec 04, 2015 at 02:36:27PM -0600, Seth Forshee wrote:
> On Fri, Dec 04, 2015 at 01:42:06PM -0600, Serge E. Hallyn wrote:
> > Quoting Seth Forshee (seth.forshee@canonical.com):
> > > A privileged user in a super block's s_user_ns is privileged
> > > towards that file system and thus should be allowed to set file
> > > capabilities. The file capabilities will not be trusted outside
> > > of s_user_ns, so an unprivileged user cannot use this to gain
> > > privileges in a user namespace where they are not already
> > > privileged.
> > > 
> > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > > ---
> > >  security/commoncap.c | 12 ++++++++----
> > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/security/commoncap.c b/security/commoncap.c
> > > index 2119421613f6..d6c80c19c449 100644
> > > --- a/security/commoncap.c
> > > +++ b/security/commoncap.c
> > > @@ -653,15 +653,17 @@ int cap_bprm_secureexec(struct linux_binprm *bprm)
> > >  int cap_inode_setxattr(struct dentry *dentry, const char *name,
> > >  		       const void *value, size_t size, int flags)
> > >  {
> > > +	struct user_namespace *user_ns = dentry->d_sb->s_user_ns;
> > > +
> > >  	if (!strcmp(name, XATTR_NAME_CAPS)) {
> > > -		if (!capable(CAP_SETFCAP))
> > > +		if (!ns_capable(user_ns, CAP_SETFCAP))
> > >  			return -EPERM;
> > 
> > This, for file capabilities, is fine,
> > 
> > >  		return 0;
> > >  	}
> > >  
> > >  	if (!strncmp(name, XATTR_SECURITY_PREFIX,
> > >  		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
> > > -	    !capable(CAP_SYS_ADMIN))
> > > +	    !ns_capable(user_ns, CAP_SYS_ADMIN))
> > 
> > but this is for all other security.*.
> > 
> > It's probably still ok, but let's think about it a sec.  MAC like
> > selinux or smack should be orthogonal to DAC.  Capabilities are the
> > same in essence, but the reason they can be treated differently here
> > is because capabilties are in fact targated at a user namespace.
> > Apparmor namespaces, for instance, are completely orthogonal to user
> > namespaces, as are contexts in selinux.
> > 
> > Now, if smack or selinux xattrs are being set then those modules
> > should be gating these writes.  Booting a kernel without those
> > modules should be a challenge for an untrusted user.  But such a
> > situation could be exploited opportunistically if it were to happen.
> > 
> > The problem with simply not changing this here is that if selinux
> > or smack authorizes the xattr write, then commoncap shouldn't be
> > denying it.
> 
> This is partly the logic behind the change, the other part being that
> the user could already insert the xattrs directly into the backing store
> so the LSMs must be prepared not to trust them in any case. But the
> commit message doesn't explain that, my mistake. And it's a question
> worth revisiting.
> 
> > I get the feeling we need cooperation among the modules (i.e. "if
> > the write is to 'security.$lsm' and $lsm is not loaded, then require
> > capable(CAP_SYS_ADMIN), else just allow)  But that's not how things are
> > structured right now.
> > 
> > Maybe security.ko could grow central logic to 'assign' security.*
> > capabilities to specific lsms and gate writes to those if $lsm is not
> > loaded.
> 
> I don't see any meaningful difference between this case and the case of
> inserting them into the backing store before mounting. We can't do
> anything to prevent the latter, so LSMs just have to be aware of
> unprivileged mounts and handle them with care. Previous patches do this
> for SELinux and Smack by adopting a policy that doesn't respect security
> labels on disk for these mounts. So I don't think that refusing to set
> security.* xattrs for an LSM that isn't loaded really accomplishes
> anything.

Good point.  I think that's the thing to point in the patch description.
(The original patch description doesn't mention any change apart from
file capabilities, which I think it should)

> Then there's the case of setting xattrs for an LSM that is currently
> loaded. I think that SELinux and Smack are both going to refuse these
> writes, Smack rather directly by seeing that the user lacks global
> CAP_MAC_ADMIN and SELinux by virtue of the fact that the previous patch
> in this series applies mountpoint labeling to these mounts. As far as I
> can tell the other LSMs don't take security policy from xattrs.
> 
> So, as far as I can tell, removing the check doesn't create any
> vulnerabilities.
> 
> But that's not to say it's the right thing to do. After reconsidering
> it, I'm inclined to be more conservative and to keep requiring
> capable(CAP_SYS_ADMIN) until such time as there's a use case for
> allowing a user privileged only in s_user_ns to write these xattrs.
> 
> > Does anything break if the second hunk in each fn in this patch is
> > not applied?
> 
> Not that I'm aware of, no.

That's ok, let's leave the patch as is, with updated description.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

thanks!

-serge

[PATCH 16/19] fuse: Add support for pid namespaces

[Seth Forshee]

If the userspace process servicing fuse requests is running in
a pid namespace then pids passed via the fuse fd need to be
translated relative to that namespace. Capture the pid namespace
in use when the filesystem is mounted and use this for pid
translation.

Since no use case currently exists for changing namespaces all
translations are done relative to the pid namespace in use when
/dev/fuse is opened. Mounting or /dev/fuse IO from another
namespace will return errors.

Requests from processes whose pid cannot be translated into the
target namespace are not permitted, except for requests
allocated via fuse_get_req_nofail_nopages. For no-fail requests
in.h.pid will be 0 if the pid translation fails.

File locking changes based on previous work done by Eric
Biederman.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/fuse/dev.c    | 19 +++++++++++++++----
 fs/fuse/file.c   | 22 +++++++++++++++++-----
 fs/fuse/fuse_i.h |  4 ++++
 fs/fuse/inode.c  |  3 +++
 4 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ebb5e37455a0..a4f6f30d6d86 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -19,6 +19,7 @@
 #include <linux/pipe_fs_i.h>
 #include <linux/swap.h>
 #include <linux/splice.h>
+#include <linux/sched.h>
 
 MODULE_ALIAS_MISCDEV(FUSE_MINOR);
 MODULE_ALIAS("devname:fuse");
@@ -124,11 +125,11 @@ static void __fuse_put_request(struct fuse_req *req)
 	atomic_dec(&req->count);
 }
 
-static void fuse_req_init_context(struct fuse_req *req)
+static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
 {
 	req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
 	req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
-	req->in.h.pid = current->pid;
+	req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
 }
 
 void fuse_set_initialized(struct fuse_conn *fc)
@@ -181,10 +182,14 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
 		goto out;
 	}
 
-	fuse_req_init_context(req);
+	fuse_req_init_context(fc, req);
 	__set_bit(FR_WAITING, &req->flags);
 	if (for_background)
 		__set_bit(FR_BACKGROUND, &req->flags);
+	if (req->in.h.pid == 0) {
+		fuse_put_request(fc, req);
+		return ERR_PTR(-EOVERFLOW);
+	}
 
 	return req;
 
@@ -274,7 +279,7 @@ struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc,
 	if (!req)
 		req = get_reserved_req(fc, file);
 
-	fuse_req_init_context(req);
+	fuse_req_init_context(fc, req);
 	__set_bit(FR_WAITING, &req->flags);
 	__clear_bit(FR_BACKGROUND, &req->flags);
 	return req;
@@ -1243,6 +1248,9 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
 	struct fuse_in *in;
 	unsigned reqsize;
 
+	if (task_active_pid_ns(current) != fc->pid_ns)
+		return -EIO;
+
  restart:
 	spin_lock(&fiq->waitq.lock);
 	err = -EAGAIN;
@@ -1872,6 +1880,9 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
 	struct fuse_req *req;
 	struct fuse_out_header oh;
 
+	if (task_active_pid_ns(current) != fc->pid_ns)
+		return -EIO;
+
 	if (nbytes < sizeof(struct fuse_out_header))
 		return -EINVAL;
 
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index e0faf8f2c868..a6c7484c94ee 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2061,7 +2061,8 @@ static int fuse_direct_mmap(struct file *file, struct vm_area_struct *vma)
 	return generic_file_mmap(file, vma);
 }
 
-static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,
+static int convert_fuse_file_lock(struct fuse_conn *fc,
+				  const struct fuse_file_lock *ffl,
 				  struct file_lock *fl)
 {
 	switch (ffl->type) {
@@ -2076,7 +2077,14 @@ static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,
 
 		fl->fl_start = ffl->start;
 		fl->fl_end = ffl->end;
-		fl->fl_pid = ffl->pid;
+
+		/*
+		 * Convert pid into the caller's pid namespace. If the pid
+		 * does not map into the namespace fl_pid will get set to 0.
+		 */
+		rcu_read_lock();
+		fl->fl_pid = pid_vnr(find_pid_ns(ffl->pid, fc->pid_ns));
+		rcu_read_unlock();
 		break;
 
 	default:
@@ -2125,7 +2133,7 @@ static int fuse_getlk(struct file *file, struct file_lock *fl)
 	args.out.args[0].value = &outarg;
 	err = fuse_simple_request(fc, &args);
 	if (!err)
-		err = convert_fuse_file_lock(&outarg.lk, fl);
+		err = convert_fuse_file_lock(fc, &outarg.lk, fl);
 
 	return err;
 }
@@ -2137,7 +2145,8 @@ static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 	FUSE_ARGS(args);
 	struct fuse_lk_in inarg;
 	int opcode = (fl->fl_flags & FL_SLEEP) ? FUSE_SETLKW : FUSE_SETLK;
-	pid_t pid = fl->fl_type != F_UNLCK ? current->tgid : 0;
+	struct pid *pid = fl->fl_type != F_UNLCK ? task_tgid(current) : NULL;
+	pid_t pid_nr = pid_nr_ns(pid, fc->pid_ns);
 	int err;
 
 	if (fl->fl_lmops && fl->fl_lmops->lm_grant) {
@@ -2149,7 +2158,10 @@ static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 	if (fl->fl_flags & FL_CLOSE)
 		return 0;
 
-	fuse_lk_fill(&args, file, fl, opcode, pid, flock, &inarg);
+	if (pid && pid_nr == 0)
+		return -EOVERFLOW;
+
+	fuse_lk_fill(&args, file, fl, opcode, pid_nr, flock, &inarg);
 	err = fuse_simple_request(fc, &args);
 
 	/* locking is restartable */
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 405113101db8..143b595197b6 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -22,6 +22,7 @@
 #include <linux/rbtree.h>
 #include <linux/poll.h>
 #include <linux/workqueue.h>
+#include <linux/pid_namespace.h>
 
 /** Max number of pages that can be used in a single read request */
 #define FUSE_MAX_PAGES_PER_REQ 32
@@ -456,6 +457,9 @@ struct fuse_conn {
 	/** The group id for this mount */
 	kgid_t group_id;
 
+	/** The pid namespace for this mount */
+	struct pid_namespace *pid_ns;
+
 	/** The fuse mount flags for this mount */
 	unsigned flags;
 
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 2913db2a5b99..2f31874ea9db 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -20,6 +20,7 @@
 #include <linux/random.h>
 #include <linux/sched.h>
 #include <linux/exportfs.h>
+#include <linux/pid_namespace.h>
 
 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
 MODULE_DESCRIPTION("Filesystem in Userspace");
@@ -609,6 +610,7 @@ void fuse_conn_init(struct fuse_conn *fc)
 	fc->connected = 1;
 	fc->attr_version = 1;
 	get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
+	fc->pid_ns = get_pid_ns(task_active_pid_ns(current));
 }
 EXPORT_SYMBOL_GPL(fuse_conn_init);
 
@@ -617,6 +619,7 @@ void fuse_conn_put(struct fuse_conn *fc)
 	if (atomic_dec_and_test(&fc->count)) {
 		if (fc->destroy_req)
 			fuse_request_free(fc->destroy_req);
+		put_pid_ns(fc->pid_ns);
 		fc->release(fc);
 	}
 }
-- 
1.9.1

[PATCH 17/19] fuse: Support fuse filesystems outside of init_user_ns

[Seth Forshee]

Update fuse to translate uids and gids to/from the user namspace
of the process servicing requests on /dev/fuse. Any ids which do
not map into the namespace will result in errors. inodes will
also be marked bad when unmappable ids are received from the
userspace fuse process.

Currently no use cases are known for letting the userspace fuse
daemon switch namespaces after opening /dev/fuse. Given this
fact, and in order to keep the implementation as simple as
possible and ease security auditing, the user namespace from
which /dev/fuse is opened is used for all id translations. This
is required to be the same namespace as s_user_ns to maintain
behavior consistent with other filesystems which can be mounted
in user namespaces.

For cuse the namespace used for the connection is also simply
current_user_ns() at the time /dev/cuse is opened.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/fuse/cuse.c   |  3 +-
 fs/fuse/dev.c    | 13 +++++----
 fs/fuse/dir.c    | 81 ++++++++++++++++++++++++++++++++++-------------------
 fs/fuse/fuse_i.h | 14 ++++++----
 fs/fuse/inode.c  | 85 ++++++++++++++++++++++++++++++++++++++++++--------------
 5 files changed, 136 insertions(+), 60 deletions(-)

diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index eae2c11268bc..a10aca57bfe4 100644
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -48,6 +48,7 @@
 #include <linux/stat.h>
 #include <linux/module.h>
 #include <linux/uio.h>
+#include <linux/user_namespace.h>
 
 #include "fuse_i.h"
 
@@ -498,7 +499,7 @@ static int cuse_channel_open(struct inode *inode, struct file *file)
 	if (!cc)
 		return -ENOMEM;
 
-	fuse_conn_init(&cc->fc);
+	fuse_conn_init(&cc->fc, current_user_ns());
 
 	fud = fuse_dev_alloc(&cc->fc);
 	if (!fud) {
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index a4f6f30d6d86..11b4cb0a0e2f 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -127,8 +127,8 @@ static void __fuse_put_request(struct fuse_req *req)
 
 static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
 {
-	req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
-	req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
+	req->in.h.uid = from_kuid(fc->user_ns, current_fsuid());
+	req->in.h.gid = from_kgid(fc->user_ns, current_fsgid());
 	req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
 }
 
@@ -186,7 +186,8 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
 	__set_bit(FR_WAITING, &req->flags);
 	if (for_background)
 		__set_bit(FR_BACKGROUND, &req->flags);
-	if (req->in.h.pid == 0) {
+	if (req->in.h.pid == 0 || req->in.h.uid == (uid_t)-1 ||
+	    req->in.h.gid == (gid_t)-1) {
 		fuse_put_request(fc, req);
 		return ERR_PTR(-EOVERFLOW);
 	}
@@ -1248,7 +1249,8 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
 	struct fuse_in *in;
 	unsigned reqsize;
 
-	if (task_active_pid_ns(current) != fc->pid_ns)
+	if (task_active_pid_ns(current) != fc->pid_ns ||
+	    current_user_ns() != fc->user_ns)
 		return -EIO;
 
  restart:
@@ -1880,7 +1882,8 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
 	struct fuse_req *req;
 	struct fuse_out_header oh;
 
-	if (task_active_pid_ns(current) != fc->pid_ns)
+	if (task_active_pid_ns(current) != fc->pid_ns ||
+	    current_user_ns() != fc->user_ns)
 		return -EIO;
 
 	if (nbytes < sizeof(struct fuse_out_header))
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 5e2e08712d3b..f67f4dd86b36 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -243,9 +243,12 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 		if (ret || (outarg.attr.mode ^ inode->i_mode) & S_IFMT)
 			goto invalid;
 
-		fuse_change_attributes(inode, &outarg.attr,
-				       entry_attr_timeout(&outarg),
-				       attr_version);
+		ret = fuse_change_attributes(inode, &outarg.attr,
+					     entry_attr_timeout(&outarg),
+					     attr_version);
+		if (ret)
+			goto invalid;
+
 		fuse_change_entry_timeout(entry, &outarg);
 	} else if (inode) {
 		fi = get_fuse_inode(inode);
@@ -319,8 +322,9 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, struct qstr *name,
 	*inode = fuse_iget(sb, outarg->nodeid, outarg->generation,
 			   &outarg->attr, entry_attr_timeout(outarg),
 			   attr_version);
-	err = -ENOMEM;
-	if (!*inode) {
+	if (IS_ERR(*inode)) {
+		err = PTR_ERR(*inode);
+		*inode = NULL;
 		fuse_queue_forget(fc, forget, outarg->nodeid, 1);
 		goto out;
 	}
@@ -441,11 +445,11 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 	ff->open_flags = outopen.open_flags;
 	inode = fuse_iget(dir->i_sb, outentry.nodeid, outentry.generation,
 			  &outentry.attr, entry_attr_timeout(&outentry), 0);
-	if (!inode) {
+	if (IS_ERR(inode)) {
 		flags &= ~(O_CREAT | O_EXCL | O_TRUNC);
 		fuse_sync_release(ff, flags);
 		fuse_queue_forget(fc, forget, outentry.nodeid, 1);
-		err = -ENOMEM;
+		err = PTR_ERR(inode);
 		goto out_err;
 	}
 	kfree(forget);
@@ -547,9 +551,9 @@ static int create_new_entry(struct fuse_conn *fc, struct fuse_args *args,
 
 	inode = fuse_iget(dir->i_sb, outarg.nodeid, outarg.generation,
 			  &outarg.attr, entry_attr_timeout(&outarg), 0);
-	if (!inode) {
+	if (IS_ERR(inode)) {
 		fuse_queue_forget(fc, forget, outarg.nodeid, 1);
-		return -ENOMEM;
+		return PTR_ERR(inode);
 	}
 	kfree(forget);
 
@@ -841,8 +845,8 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
 	stat->ino = attr->ino;
 	stat->mode = (inode->i_mode & S_IFMT) | (attr->mode & 07777);
 	stat->nlink = attr->nlink;
-	stat->uid = make_kuid(&init_user_ns, attr->uid);
-	stat->gid = make_kgid(&init_user_ns, attr->gid);
+	stat->uid = inode->i_uid;
+	stat->gid = inode->i_gid;
 	stat->rdev = inode->i_rdev;
 	stat->atime.tv_sec = attr->atime;
 	stat->atime.tv_nsec = attr->atimensec;
@@ -896,10 +900,10 @@ static int fuse_do_getattr(struct inode *inode, struct kstat *stat,
 			make_bad_inode(inode);
 			err = -EIO;
 		} else {
-			fuse_change_attributes(inode, &outarg.attr,
-					       attr_timeout(&outarg),
-					       attr_version);
-			if (stat)
+			err = fuse_change_attributes(inode, &outarg.attr,
+						     attr_timeout(&outarg),
+						     attr_version);
+			if (!err && stat)
 				fuse_fillattr(inode, &outarg.attr, stat);
 		}
 	}
@@ -1221,9 +1225,11 @@ static int fuse_direntplus_link(struct file *file,
 			fi->nlookup++;
 			spin_unlock(&fc->lock);
 
-			fuse_change_attributes(inode, &o->attr,
-					       entry_attr_timeout(o),
-					       attr_version);
+			err = fuse_change_attributes(inode, &o->attr,
+						     entry_attr_timeout(o),
+						     attr_version);
+			if (err)
+				goto out;
 
 			/*
 			 * The other branch to 'found' comes via fuse_iget()
@@ -1241,8 +1247,10 @@ static int fuse_direntplus_link(struct file *file,
 
 	inode = fuse_iget(dir->i_sb, o->nodeid, o->generation,
 			  &o->attr, entry_attr_timeout(o), attr_version);
-	if (!inode)
+	if (IS_ERR(inode)) {
+		err = PTR_ERR(inode);
 		goto out;
+	}
 
 	alias = d_splice_alias(inode, dentry);
 	err = PTR_ERR(alias);
@@ -1455,17 +1463,25 @@ static bool update_mtime(unsigned ivalid, bool trust_local_mtime)
 	return true;
 }
 
-static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg,
-			   bool trust_local_cmtime)
+static int iattr_to_fattr(struct fuse_conn *fc, struct iattr *iattr,
+			   struct fuse_setattr_in *arg, bool trust_local_cmtime)
 {
 	unsigned ivalid = iattr->ia_valid;
 
 	if (ivalid & ATTR_MODE)
 		arg->valid |= FATTR_MODE,   arg->mode = iattr->ia_mode;
-	if (ivalid & ATTR_UID)
-		arg->valid |= FATTR_UID,    arg->uid = from_kuid(&init_user_ns, iattr->ia_uid);
-	if (ivalid & ATTR_GID)
-		arg->valid |= FATTR_GID,    arg->gid = from_kgid(&init_user_ns, iattr->ia_gid);
+	if (ivalid & ATTR_UID) {
+		arg->uid = from_kuid(fc->user_ns, iattr->ia_uid);
+		if (arg->uid == (uid_t)-1)
+			return -EINVAL;
+		arg->valid |= FATTR_UID;
+	}
+	if (ivalid & ATTR_GID) {
+		arg->gid = from_kgid(fc->user_ns, iattr->ia_gid);
+		if (arg->gid == (gid_t)-1)
+			return -EINVAL;
+		arg->valid |= FATTR_GID;
+	}
 	if (ivalid & ATTR_SIZE)
 		arg->valid |= FATTR_SIZE,   arg->size = iattr->ia_size;
 	if (ivalid & ATTR_ATIME) {
@@ -1487,6 +1503,8 @@ static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg,
 		arg->ctime = iattr->ia_ctime.tv_sec;
 		arg->ctimensec = iattr->ia_ctime.tv_nsec;
 	}
+
+	return 0;
 }
 
 /*
@@ -1625,7 +1643,9 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
 
 	memset(&inarg, 0, sizeof(inarg));
 	memset(&outarg, 0, sizeof(outarg));
-	iattr_to_fattr(attr, &inarg, trust_local_cmtime);
+	err = iattr_to_fattr(fc, attr, &inarg, trust_local_cmtime);
+	if (err)
+		goto error;
 	if (file) {
 		struct fuse_file *ff = file->private_data;
 		inarg.valid |= FATTR_FH;
@@ -1660,8 +1680,13 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
 		/* FIXME: clear I_DIRTY_SYNC? */
 	}
 
-	fuse_change_attributes_common(inode, &outarg.attr,
-				      attr_timeout(&outarg));
+	err = fuse_change_attributes_common(inode, &outarg.attr,
+				            attr_timeout(&outarg));
+	if (err) {
+		spin_unlock(&fc->lock);
+		goto error;
+	}
+
 	oldsize = inode->i_size;
 	/* see the comment in fuse_change_attributes() */
 	if (!is_wb || is_truncate || !S_ISREG(inode->i_mode))
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 143b595197b6..98c669ccfe7f 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -23,6 +23,7 @@
 #include <linux/poll.h>
 #include <linux/workqueue.h>
 #include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
 
 /** Max number of pages that can be used in a single read request */
 #define FUSE_MAX_PAGES_PER_REQ 32
@@ -460,6 +461,9 @@ struct fuse_conn {
 	/** The pid namespace for this mount */
 	struct pid_namespace *pid_ns;
 
+	/** The user namespace for this mount */
+	struct user_namespace *user_ns;
+
 	/** The fuse mount flags for this mount */
 	unsigned flags;
 
@@ -761,11 +765,11 @@ void fuse_init_symlink(struct inode *inode);
 /**
  * Change attributes of an inode
  */
-void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
-			    u64 attr_valid, u64 attr_version);
+int fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
+			   u64 attr_valid, u64 attr_version);
 
-void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
-				   u64 attr_valid);
+int fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
+				  u64 attr_valid);
 
 /**
  * Initialize the client device
@@ -855,7 +859,7 @@ struct fuse_conn *fuse_conn_get(struct fuse_conn *fc);
 /**
  * Initialize fuse_conn
  */
-void fuse_conn_init(struct fuse_conn *fc);
+void fuse_conn_init(struct fuse_conn *fc, struct user_namespace *user_ns);
 
 /**
  * Release reference to fuse_conn
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 2f31874ea9db..ea61a7639a8e 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -155,11 +155,22 @@ static ino_t fuse_squash_ino(u64 ino64)
 	return ino;
 }
 
-void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
-				   u64 attr_valid)
+int fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
+				  u64 attr_valid)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_inode *fi = get_fuse_inode(inode);
+	kuid_t uid;
+	kgid_t gid;
+
+	uid = make_kuid(fc->user_ns, attr->uid);
+	gid = make_kgid(fc->user_ns, attr->gid);
+	if (!uid_valid(uid) || !gid_valid(gid)) {
+		make_bad_inode(inode);
+		return -EIO;
+	}
+	inode->i_uid = uid;
+	inode->i_gid = gid;
 
 	fi->attr_version = ++fc->attr_version;
 	fi->i_time = attr_valid;
@@ -167,8 +178,6 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
 	inode->i_ino     = fuse_squash_ino(attr->ino);
 	inode->i_mode    = (inode->i_mode & S_IFMT) | (attr->mode & 07777);
 	set_nlink(inode, attr->nlink);
-	inode->i_uid     = make_kuid(&init_user_ns, attr->uid);
-	inode->i_gid     = make_kgid(&init_user_ns, attr->gid);
 	inode->i_blocks  = attr->blocks;
 	inode->i_atime.tv_sec   = attr->atime;
 	inode->i_atime.tv_nsec  = attr->atimensec;
@@ -195,26 +204,32 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
 		inode->i_mode &= ~S_ISVTX;
 
 	fi->orig_ino = attr->ino;
+	return 0;
 }
 
-void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
-			    u64 attr_valid, u64 attr_version)
+int fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
+			   u64 attr_valid, u64 attr_version)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_inode *fi = get_fuse_inode(inode);
 	bool is_wb = fc->writeback_cache;
 	loff_t oldsize;
 	struct timespec old_mtime;
+	int err;
 
 	spin_lock(&fc->lock);
 	if ((attr_version != 0 && fi->attr_version > attr_version) ||
 	    test_bit(FUSE_I_SIZE_UNSTABLE, &fi->state)) {
 		spin_unlock(&fc->lock);
-		return;
+		return 0;
 	}
 
 	old_mtime = inode->i_mtime;
-	fuse_change_attributes_common(inode, attr, attr_valid);
+	err = fuse_change_attributes_common(inode, attr, attr_valid);
+	if (err) {
+		spin_unlock(&fc->lock);
+		return err;
+	}
 
 	oldsize = inode->i_size;
 	/*
@@ -249,6 +264,8 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
 		if (inval)
 			invalidate_inode_pages2(inode->i_mapping);
 	}
+
+	return 0;
 }
 
 static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)
@@ -302,7 +319,7 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
  retry:
 	inode = iget5_locked(sb, nodeid, fuse_inode_eq, fuse_inode_set, &nodeid);
 	if (!inode)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	if ((inode->i_state & I_NEW)) {
 		inode->i_flags |= S_NOATIME;
@@ -318,11 +335,23 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
 		goto retry;
 	}
 
+	/*
+	 * Must do this before incrementing nlookup, as the caller will
+	 * send a forget for the node if this function fails.
+	 */
+	if (fuse_change_attributes(inode, attr, attr_valid, attr_version)) {
+		/*
+		 * inode_make_bad() already called by
+		 * fuse_change_attributes()
+		 */
+		iput(inode);
+		return ERR_PTR(-EIO);
+	}
+
 	fi = get_fuse_inode(inode);
 	spin_lock(&fc->lock);
 	fi->nlookup++;
 	spin_unlock(&fc->lock);
-	fuse_change_attributes(inode, attr, attr_valid, attr_version);
 
 	return inode;
 }
@@ -467,12 +496,15 @@ static int fuse_match_uint(substring_t *s, unsigned int *res)
 	return err;
 }
 
-static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
+static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev,
+			  struct user_namespace *user_ns)
 {
 	char *p;
 	memset(d, 0, sizeof(struct fuse_mount_data));
 	d->max_read = ~0;
 	d->blksize = FUSE_DEFAULT_BLKSIZE;
+	d->user_id = make_kuid(user_ns, 0);
+	d->group_id = make_kgid(user_ns, 0);
 
 	while ((p = strsep(&opt, ",")) != NULL) {
 		int token;
@@ -503,7 +535,7 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
 		case OPT_USER_ID:
 			if (fuse_match_uint(&args[0], &uv))
 				return 0;
-			d->user_id = make_kuid(current_user_ns(), uv);
+			d->user_id = make_kuid(user_ns, uv);
 			if (!uid_valid(d->user_id))
 				return 0;
 			d->user_id_present = 1;
@@ -512,7 +544,7 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
 		case OPT_GROUP_ID:
 			if (fuse_match_uint(&args[0], &uv))
 				return 0;
-			d->group_id = make_kgid(current_user_ns(), uv);
+			d->group_id = make_kgid(user_ns, uv);
 			if (!gid_valid(d->group_id))
 				return 0;
 			d->group_id_present = 1;
@@ -555,8 +587,10 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
 	struct super_block *sb = root->d_sb;
 	struct fuse_conn *fc = get_fuse_conn_super(sb);
 
-	seq_printf(m, ",user_id=%u", from_kuid_munged(&init_user_ns, fc->user_id));
-	seq_printf(m, ",group_id=%u", from_kgid_munged(&init_user_ns, fc->group_id));
+	seq_printf(m, ",user_id=%u",
+		   from_kuid_munged(fc->user_ns, fc->user_id));
+	seq_printf(m, ",group_id=%u",
+		   from_kgid_munged(fc->user_ns, fc->group_id));
 	if (fc->flags & FUSE_DEFAULT_PERMISSIONS)
 		seq_puts(m, ",default_permissions");
 	if (fc->flags & FUSE_ALLOW_OTHER)
@@ -587,7 +621,7 @@ static void fuse_pqueue_init(struct fuse_pqueue *fpq)
 	fpq->connected = 1;
 }
 
-void fuse_conn_init(struct fuse_conn *fc)
+void fuse_conn_init(struct fuse_conn *fc, struct user_namespace *user_ns)
 {
 	memset(fc, 0, sizeof(*fc));
 	spin_lock_init(&fc->lock);
@@ -611,6 +645,7 @@ void fuse_conn_init(struct fuse_conn *fc)
 	fc->attr_version = 1;
 	get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
 	fc->pid_ns = get_pid_ns(task_active_pid_ns(current));
+	fc->user_ns = get_user_ns(user_ns);
 }
 EXPORT_SYMBOL_GPL(fuse_conn_init);
 
@@ -620,6 +655,7 @@ void fuse_conn_put(struct fuse_conn *fc)
 		if (fc->destroy_req)
 			fuse_request_free(fc->destroy_req);
 		put_pid_ns(fc->pid_ns);
+		put_user_ns(fc->user_ns);
 		fc->release(fc);
 	}
 }
@@ -635,12 +671,15 @@ EXPORT_SYMBOL_GPL(fuse_conn_get);
 static struct inode *fuse_get_root_inode(struct super_block *sb, unsigned mode)
 {
 	struct fuse_attr attr;
+	struct inode *inode;
+
 	memset(&attr, 0, sizeof(attr));
 
 	attr.mode = mode;
 	attr.ino = FUSE_ROOT_ID;
 	attr.nlink = 1;
-	return fuse_iget(sb, 1, 0, &attr, 0, 0);
+	inode = fuse_iget(sb, 1, 0, &attr, 0, 0);
+	return IS_ERR(inode) ? NULL : inode;
 }
 
 struct fuse_inode_handle {
@@ -1046,7 +1085,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 
 	sb->s_flags &= ~(MS_NOSEC | MS_I_VERSION);
 
-	if (!parse_fuse_opt(data, &d, is_bdev))
+	if (!parse_fuse_opt(data, &d, is_bdev, sb->s_user_ns))
 		goto err;
 
 	if (is_bdev) {
@@ -1070,8 +1109,12 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 	if (!file)
 		goto err;
 
-	if ((file->f_op != &fuse_dev_operations) ||
-	    (file->f_cred->user_ns != &init_user_ns))
+	/*
+	 * Require mount to happen from the same user namespace which
+	 * opened /dev/fuse to prevent potential attacks.
+	 */
+	if (file->f_op != &fuse_dev_operations ||
+	    file->f_cred->user_ns != sb->s_user_ns)
 		goto err_fput;
 
 	fc = kmalloc(sizeof(*fc), GFP_KERNEL);
@@ -1079,7 +1122,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 	if (!fc)
 		goto err_fput;
 
-	fuse_conn_init(fc);
+	fuse_conn_init(fc, sb->s_user_ns);
 	fc->release = fuse_free_conn;
 
 	fud = fuse_dev_alloc(fc);
-- 
1.9.1

Re: [PATCH 17/19] fuse: Support fuse filesystems outside of init_user_ns

[Seth Forshee]

On Wed, Dec 02, 2015 at 09:40:17AM -0600, Seth Forshee wrote:
> @@ -155,11 +155,22 @@ static ino_t fuse_squash_ino(u64 ino64)
>  	return ino;
>  }
>  
> -void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
> -				   u64 attr_valid)
> +int fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
> +				  u64 attr_valid)
>  {
>  	struct fuse_conn *fc = get_fuse_conn(inode);
>  	struct fuse_inode *fi = get_fuse_inode(inode);
> +	kuid_t uid;
> +	kgid_t gid;
> +
> +	uid = make_kuid(fc->user_ns, attr->uid);
> +	gid = make_kgid(fc->user_ns, attr->gid);
> +	if (!uid_valid(uid) || !gid_valid(gid)) {
> +		make_bad_inode(inode);
> +		return -EIO;
> +	}

Eric - I had kind of forgotten about this part until just now, but
previously with these patches we had discussed how to handle ids from
the filesystem that aren't valid in s_user_ns. My intention is to set
the kuids in the inode to invalid, and in these patches I've updated the
vfs so that it should be safe to do that. But at some point I think you
had suggested marking the inodes bad, and I must have added this as a
result. I guess we need to decide which way to go. I favor using invalid
ids so that a user privileged in s_user_ns can still access the inode,
change ownership, etc., but I'm interested to hear your opinion.

Thanks,
Seth

Re: [PATCH 17/19] fuse: Support fuse filesystems outside of init_user_ns

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> Update fuse to translate uids and gids to/from the user namspace
> of the process servicing requests on /dev/fuse. Any ids which do
> not map into the namespace will result in errors. inodes will
> also be marked bad when unmappable ids are received from the
> userspace fuse process.
> 
> Currently no use cases are known for letting the userspace fuse
> daemon switch namespaces after opening /dev/fuse. Given this
> fact, and in order to keep the implementation as simple as
> possible and ease security auditing, the user namespace from
> which /dev/fuse is opened is used for all id translations. This
> is required to be the same namespace as s_user_ns to maintain
> behavior consistent with other filesystems which can be mounted
> in user namespaces.
> 
> For cuse the namespace used for the connection is also simply
> current_user_ns() at the time /dev/cuse is opened.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> ---
>  fs/fuse/cuse.c   |  3 +-
>  fs/fuse/dev.c    | 13 +++++----
>  fs/fuse/dir.c    | 81 ++++++++++++++++++++++++++++++++++-------------------
>  fs/fuse/fuse_i.h | 14 ++++++----
>  fs/fuse/inode.c  | 85 ++++++++++++++++++++++++++++++++++++++++++--------------
>  5 files changed, 136 insertions(+), 60 deletions(-)
> 
> diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
> index eae2c11268bc..a10aca57bfe4 100644
> --- a/fs/fuse/cuse.c
> +++ b/fs/fuse/cuse.c
> @@ -48,6 +48,7 @@
>  #include <linux/stat.h>
>  #include <linux/module.h>
>  #include <linux/uio.h>
> +#include <linux/user_namespace.h>
>  
>  #include "fuse_i.h"
>  
> @@ -498,7 +499,7 @@ static int cuse_channel_open(struct inode *inode, struct file *file)
>  	if (!cc)
>  		return -ENOMEM;
>  
> -	fuse_conn_init(&cc->fc);
> +	fuse_conn_init(&cc->fc, current_user_ns());
>  
>  	fud = fuse_dev_alloc(&cc->fc);
>  	if (!fud) {
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index a4f6f30d6d86..11b4cb0a0e2f 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -127,8 +127,8 @@ static void __fuse_put_request(struct fuse_req *req)
>  
>  static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
>  {
> -	req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
> -	req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
> +	req->in.h.uid = from_kuid(fc->user_ns, current_fsuid());
> +	req->in.h.gid = from_kgid(fc->user_ns, current_fsgid());
>  	req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
>  }
>  
> @@ -186,7 +186,8 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
>  	__set_bit(FR_WAITING, &req->flags);
>  	if (for_background)
>  		__set_bit(FR_BACKGROUND, &req->flags);
> -	if (req->in.h.pid == 0) {
> +	if (req->in.h.pid == 0 || req->in.h.uid == (uid_t)-1 ||
> +	    req->in.h.gid == (gid_t)-1) {
>  		fuse_put_request(fc, req);
>  		return ERR_PTR(-EOVERFLOW);
>  	}
> @@ -1248,7 +1249,8 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
>  	struct fuse_in *in;
>  	unsigned reqsize;
>  
> -	if (task_active_pid_ns(current) != fc->pid_ns)
> +	if (task_active_pid_ns(current) != fc->pid_ns ||
> +	    current_user_ns() != fc->user_ns)

Do you think this should be using current_in_user_ns(fc->user_ns) ?

Opening a file, forking (maybe unsharing) then acting on the file is
pretty standard fare which this would break.

(same for pidns, i guess, as well as for write below)

>  		return -EIO;
>  
>   restart:
> @@ -1880,7 +1882,8 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
>  	struct fuse_req *req;
>  	struct fuse_out_header oh;
>  
> -	if (task_active_pid_ns(current) != fc->pid_ns)
> +	if (task_active_pid_ns(current) != fc->pid_ns ||
> +	    current_user_ns() != fc->user_ns)
>  		return -EIO;
>  
>  	if (nbytes < sizeof(struct fuse_out_header))

Re: [PATCH 17/19] fuse: Support fuse filesystems outside of init_user_ns

[Seth Forshee]

On Fri, Dec 04, 2015 at 02:03:55PM -0600, Serge E. Hallyn wrote:
> Quoting Seth Forshee (seth.forshee@canonical.com):
> > Update fuse to translate uids and gids to/from the user namspace
> > of the process servicing requests on /dev/fuse. Any ids which do
> > not map into the namespace will result in errors. inodes will
> > also be marked bad when unmappable ids are received from the
> > userspace fuse process.
> > 
> > Currently no use cases are known for letting the userspace fuse
> > daemon switch namespaces after opening /dev/fuse. Given this
> > fact, and in order to keep the implementation as simple as
> > possible and ease security auditing, the user namespace from
> > which /dev/fuse is opened is used for all id translations. This
> > is required to be the same namespace as s_user_ns to maintain
> > behavior consistent with other filesystems which can be mounted
> > in user namespaces.
> > 
> > For cuse the namespace used for the connection is also simply
> > current_user_ns() at the time /dev/cuse is opened.
> > 
> > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > ---
> >  fs/fuse/cuse.c   |  3 +-
> >  fs/fuse/dev.c    | 13 +++++----
> >  fs/fuse/dir.c    | 81 ++++++++++++++++++++++++++++++++++-------------------
> >  fs/fuse/fuse_i.h | 14 ++++++----
> >  fs/fuse/inode.c  | 85 ++++++++++++++++++++++++++++++++++++++++++--------------
> >  5 files changed, 136 insertions(+), 60 deletions(-)
> > 
> > diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
> > index eae2c11268bc..a10aca57bfe4 100644
> > --- a/fs/fuse/cuse.c
> > +++ b/fs/fuse/cuse.c
> > @@ -48,6 +48,7 @@
> >  #include <linux/stat.h>
> >  #include <linux/module.h>
> >  #include <linux/uio.h>
> > +#include <linux/user_namespace.h>
> >  
> >  #include "fuse_i.h"
> >  
> > @@ -498,7 +499,7 @@ static int cuse_channel_open(struct inode *inode, struct file *file)
> >  	if (!cc)
> >  		return -ENOMEM;
> >  
> > -	fuse_conn_init(&cc->fc);
> > +	fuse_conn_init(&cc->fc, current_user_ns());
> >  
> >  	fud = fuse_dev_alloc(&cc->fc);
> >  	if (!fud) {
> > diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> > index a4f6f30d6d86..11b4cb0a0e2f 100644
> > --- a/fs/fuse/dev.c
> > +++ b/fs/fuse/dev.c
> > @@ -127,8 +127,8 @@ static void __fuse_put_request(struct fuse_req *req)
> >  
> >  static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
> >  {
> > -	req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
> > -	req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
> > +	req->in.h.uid = from_kuid(fc->user_ns, current_fsuid());
> > +	req->in.h.gid = from_kgid(fc->user_ns, current_fsgid());
> >  	req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
> >  }
> >  
> > @@ -186,7 +186,8 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
> >  	__set_bit(FR_WAITING, &req->flags);
> >  	if (for_background)
> >  		__set_bit(FR_BACKGROUND, &req->flags);
> > -	if (req->in.h.pid == 0) {
> > +	if (req->in.h.pid == 0 || req->in.h.uid == (uid_t)-1 ||
> > +	    req->in.h.gid == (gid_t)-1) {
> >  		fuse_put_request(fc, req);
> >  		return ERR_PTR(-EOVERFLOW);
> >  	}
> > @@ -1248,7 +1249,8 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
> >  	struct fuse_in *in;
> >  	unsigned reqsize;
> >  
> > -	if (task_active_pid_ns(current) != fc->pid_ns)
> > +	if (task_active_pid_ns(current) != fc->pid_ns ||
> > +	    current_user_ns() != fc->user_ns)
> 
> Do you think this should be using current_in_user_ns(fc->user_ns) ?
> 
> Opening a file, forking (maybe unsharing) then acting on the file is
> pretty standard fare which this would break.
> 
> (same for pidns, i guess, as well as for write below)

I'd rather leave it as is. It might be okay, but even if current_user_ns
is a child of fc->user_ns it could end up seeing ids that aren't valid
for it's namespaces, and that might cause issues for filesystems which
aren't expecting it.

But if you have a use case for a process in a child namespace servicing
requests for a mount, I'd be willing to reconsider.

Re: [PATCH 17/19] fuse: Support fuse filesystems outside of init_user_ns

[Serge E. Hallyn]

On Fri, Dec 04, 2015 at 02:41:22PM -0600, Seth Forshee wrote:
> On Fri, Dec 04, 2015 at 02:03:55PM -0600, Serge E. Hallyn wrote:
> > Quoting Seth Forshee (seth.forshee@canonical.com):
> > > Update fuse to translate uids and gids to/from the user namspace
> > > of the process servicing requests on /dev/fuse. Any ids which do
> > > not map into the namespace will result in errors. inodes will
> > > also be marked bad when unmappable ids are received from the
> > > userspace fuse process.
> > > 
> > > Currently no use cases are known for letting the userspace fuse
> > > daemon switch namespaces after opening /dev/fuse. Given this
> > > fact, and in order to keep the implementation as simple as
> > > possible and ease security auditing, the user namespace from
> > > which /dev/fuse is opened is used for all id translations. This
> > > is required to be the same namespace as s_user_ns to maintain
> > > behavior consistent with other filesystems which can be mounted
> > > in user namespaces.
> > > 
> > > For cuse the namespace used for the connection is also simply
> > > current_user_ns() at the time /dev/cuse is opened.
> > > 
> > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > > ---
> > >  fs/fuse/cuse.c   |  3 +-
> > >  fs/fuse/dev.c    | 13 +++++----
> > >  fs/fuse/dir.c    | 81 ++++++++++++++++++++++++++++++++++-------------------
> > >  fs/fuse/fuse_i.h | 14 ++++++----
> > >  fs/fuse/inode.c  | 85 ++++++++++++++++++++++++++++++++++++++++++--------------
> > >  5 files changed, 136 insertions(+), 60 deletions(-)
> > > 
> > > diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
> > > index eae2c11268bc..a10aca57bfe4 100644
> > > --- a/fs/fuse/cuse.c
> > > +++ b/fs/fuse/cuse.c
> > > @@ -48,6 +48,7 @@
> > >  #include <linux/stat.h>
> > >  #include <linux/module.h>
> > >  #include <linux/uio.h>
> > > +#include <linux/user_namespace.h>
> > >  
> > >  #include "fuse_i.h"
> > >  
> > > @@ -498,7 +499,7 @@ static int cuse_channel_open(struct inode *inode, struct file *file)
> > >  	if (!cc)
> > >  		return -ENOMEM;
> > >  
> > > -	fuse_conn_init(&cc->fc);
> > > +	fuse_conn_init(&cc->fc, current_user_ns());
> > >  
> > >  	fud = fuse_dev_alloc(&cc->fc);
> > >  	if (!fud) {
> > > diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> > > index a4f6f30d6d86..11b4cb0a0e2f 100644
> > > --- a/fs/fuse/dev.c
> > > +++ b/fs/fuse/dev.c
> > > @@ -127,8 +127,8 @@ static void __fuse_put_request(struct fuse_req *req)
> > >  
> > >  static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
> > >  {
> > > -	req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
> > > -	req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
> > > +	req->in.h.uid = from_kuid(fc->user_ns, current_fsuid());
> > > +	req->in.h.gid = from_kgid(fc->user_ns, current_fsgid());
> > >  	req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
> > >  }
> > >  
> > > @@ -186,7 +186,8 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
> > >  	__set_bit(FR_WAITING, &req->flags);
> > >  	if (for_background)
> > >  		__set_bit(FR_BACKGROUND, &req->flags);
> > > -	if (req->in.h.pid == 0) {
> > > +	if (req->in.h.pid == 0 || req->in.h.uid == (uid_t)-1 ||
> > > +	    req->in.h.gid == (gid_t)-1) {
> > >  		fuse_put_request(fc, req);
> > >  		return ERR_PTR(-EOVERFLOW);
> > >  	}
> > > @@ -1248,7 +1249,8 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
> > >  	struct fuse_in *in;
> > >  	unsigned reqsize;
> > >  
> > > -	if (task_active_pid_ns(current) != fc->pid_ns)
> > > +	if (task_active_pid_ns(current) != fc->pid_ns ||
> > > +	    current_user_ns() != fc->user_ns)
> > 
> > Do you think this should be using current_in_user_ns(fc->user_ns) ?
> > 
> > Opening a file, forking (maybe unsharing) then acting on the file is
> > pretty standard fare which this would break.
> > 
> > (same for pidns, i guess, as well as for write below)
> 
> I'd rather leave it as is. It might be okay, but even if current_user_ns
> is a child of fc->user_ns it could end up seeing ids that aren't valid
> for it's namespaces, and that might cause issues for filesystems which
> aren't expecting it.
> 
> But if you have a use case for a process in a child namespace servicing
> requests for a mount, I'd be willing to reconsider.

I'm pretty sure we'll get such uses, i.e. opening a file, unsharing userns,
and not mapping in any userids, to sandbox the program.  But we can address
it when it happens, I think.

(sorry I need to re-read before acking the whole patch)

[PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

[Seth Forshee]

Unprivileged users are normally restricted from mounting with the
allow_other option by system policy, but this could be bypassed
for a mount done with user namespace root permissions. In such
cases allow_other should not allow users outside the userns
to access the mount as doing so would give the unprivileged user
the ability to manipulate processes it would otherwise be unable
to manipulate. Restrict allow_other to apply to users in the same
userns used at mount or a descendant of that namespace.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/fuse/dir.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index f67f4dd86b36..5b8edb1203b8 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1018,8 +1018,14 @@ int fuse_allow_current_process(struct fuse_conn *fc)
 {
 	const struct cred *cred;
 
-	if (fc->flags & FUSE_ALLOW_OTHER)
-		return 1;
+	if (fc->flags & FUSE_ALLOW_OTHER) {
+		struct user_namespace *ns;
+		for (ns = current_user_ns(); ns; ns = ns->parent) {
+			if (ns == fc->user_ns)
+				return 1;
+		}
+		return 0;
+	}
 
 	cred = current_cred();
 	if (uid_eq(cred->euid, fc->user_id) &&
-- 
1.9.1

Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

[Serge E. Hallyn]

Quoting Seth Forshee (seth.forshee@canonical.com):
> Unprivileged users are normally restricted from mounting with the
> allow_other option by system policy, but this could be bypassed
> for a mount done with user namespace root permissions. In such
> cases allow_other should not allow users outside the userns
> to access the mount as doing so would give the unprivileged user
> the ability to manipulate processes it would otherwise be unable
> to manipulate. Restrict allow_other to apply to users in the same
> userns used at mount or a descendant of that namespace.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> ---
>  fs/fuse/dir.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index f67f4dd86b36..5b8edb1203b8 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -1018,8 +1018,14 @@ int fuse_allow_current_process(struct fuse_conn *fc)
>  {
>  	const struct cred *cred;
>  
> -	if (fc->flags & FUSE_ALLOW_OTHER)
> -		return 1;
> +	if (fc->flags & FUSE_ALLOW_OTHER) {
> +		struct user_namespace *ns;
> +		for (ns = current_user_ns(); ns; ns = ns->parent) {
> +			if (ns == fc->user_ns)
> +				return 1;
> +		}

	use current_in_userns() ?

> +		return 0;
> +	}
>  
>  	cred = current_cred();
>  	if (uid_eq(cred->euid, fc->user_id) &&
> -- 
> 1.9.1
> 
> --
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Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

[Seth Forshee]

On Fri, Dec 04, 2015 at 02:05:41PM -0600, Serge E. Hallyn wrote:
> Quoting Seth Forshee (seth.forshee@canonical.com):
> > Unprivileged users are normally restricted from mounting with the
> > allow_other option by system policy, but this could be bypassed
> > for a mount done with user namespace root permissions. In such
> > cases allow_other should not allow users outside the userns
> > to access the mount as doing so would give the unprivileged user
> > the ability to manipulate processes it would otherwise be unable
> > to manipulate. Restrict allow_other to apply to users in the same
> > userns used at mount or a descendant of that namespace.
> > 
> > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > ---
> >  fs/fuse/dir.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> > index f67f4dd86b36..5b8edb1203b8 100644
> > --- a/fs/fuse/dir.c
> > +++ b/fs/fuse/dir.c
> > @@ -1018,8 +1018,14 @@ int fuse_allow_current_process(struct fuse_conn *fc)
> >  {
> >  	const struct cred *cred;
> >  
> > -	if (fc->flags & FUSE_ALLOW_OTHER)
> > -		return 1;
> > +	if (fc->flags & FUSE_ALLOW_OTHER) {
> > +		struct user_namespace *ns;
> > +		for (ns = current_user_ns(); ns; ns = ns->parent) {
> > +			if (ns == fc->user_ns)
> > +				return 1;
> > +		}
> 
> 	use current_in_userns() ?

Yes, it should. I wrote this before I wrote the patch which adds that
function and never thought to go back to change it here.

Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

[Serge E. Hallyn]

On Fri, Dec 04, 2015 at 02:43:19PM -0600, Seth Forshee wrote:
> On Fri, Dec 04, 2015 at 02:05:41PM -0600, Serge E. Hallyn wrote:
> > Quoting Seth Forshee (seth.forshee@canonical.com):
> > > Unprivileged users are normally restricted from mounting with the
> > > allow_other option by system policy, but this could be bypassed
> > > for a mount done with user namespace root permissions. In such
> > > cases allow_other should not allow users outside the userns
> > > to access the mount as doing so would give the unprivileged user
> > > the ability to manipulate processes it would otherwise be unable
> > > to manipulate. Restrict allow_other to apply to users in the same
> > > userns used at mount or a descendant of that namespace.
> > > 
> > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > > ---
> > >  fs/fuse/dir.c | 10 ++++++++--
> > >  1 file changed, 8 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> > > index f67f4dd86b36..5b8edb1203b8 100644
> > > --- a/fs/fuse/dir.c
> > > +++ b/fs/fuse/dir.c
> > > @@ -1018,8 +1018,14 @@ int fuse_allow_current_process(struct fuse_conn *fc)
> > >  {
> > >  	const struct cred *cred;
> > >  
> > > -	if (fc->flags & FUSE_ALLOW_OTHER)
> > > -		return 1;
> > > +	if (fc->flags & FUSE_ALLOW_OTHER) {
> > > +		struct user_namespace *ns;
> > > +		for (ns = current_user_ns(); ns; ns = ns->parent) {
> > > +			if (ns == fc->user_ns)
> > > +				return 1;
> > > +		}
> > 
> > 	use current_in_userns() ?
> 
> Yes, it should. I wrote this before I wrote the patch which adds that
> function and never thought to go back to change it here.

Ok - 

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

thanks.

[PATCH 19/19] fuse: Allow user namespace mounts

[Seth Forshee]

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/fuse/inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index ea61a7639a8e..ffce4354563e 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1233,7 +1233,7 @@ static void fuse_kill_sb_anon(struct super_block *sb)
 static struct file_system_type fuse_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "fuse",
-	.fs_flags	= FS_HAS_SUBTYPE,
+	.fs_flags	= FS_HAS_SUBTYPE | FS_USERNS_MOUNT,
 	.mount		= fuse_mount,
 	.kill_sb	= fuse_kill_sb_anon,
 };
@@ -1265,7 +1265,7 @@ static struct file_system_type fuseblk_fs_type = {
 	.name		= "fuseblk",
 	.mount		= fuse_mount_blk,
 	.kill_sb	= fuse_kill_sb_blk,
-	.fs_flags	= FS_REQUIRES_DEV | FS_HAS_SUBTYPE,
+	.fs_flags	= FS_REQUIRES_DEV | FS_HAS_SUBTYPE | FS_USERNS_MOUNT,
 };
 MODULE_ALIAS_FS("fuseblk");
 
-- 
1.9.1