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

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Quoting Miklos Szeredi (miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org):
> From: Miklos Szeredi <mszeredi-AlSwsSmVLrQ@public.gmane.org>
> 
> On mount propagation, let the owner of the clone be inherited from the
> parent into which it has been propagated.  Also if the parent has the
> "nosuid" flag, set this flag for the child as well.

What about nodev?

thanks,
-serge

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