Commit 44dfd84a authored by David Howells's avatar David Howells Committed by Al Viro
Browse files

teach move_mount(2) to work with OPEN_TREE_CLONE 



Allow a detached tree created by open_tree(..., OPEN_TREE_CLONE) to be
attached by move_mount(2).

If by the time of final fput() of OPEN_TREE_CLONE-opened file its tree is
not detached anymore, it won't be dissolved.  move_mount(2) is adjusted
to handle detached source.

That gives us equivalents of mount --bind and mount --rbind.

Thanks also to Alan Jenkins <alan.christopher.jenkins@gmail.com> for
providing a whole bunch of ways to break things using this interface.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 2db154b3

fs/namespace.c

+55 −7
Original line number Diff line number Diff line
@@ -1842,9 +1842,15 @@ void dissolve_on_fput(struct vfsmount *mnt) 
	namespace_lock();

	lock_mount_hash();

	ns = real_mount(mnt)->mnt_ns;

	if (ns) {

		if (is_anon_ns(ns))

			umount_tree(real_mount(mnt), UMOUNT_CONNECTED);

		else

			ns = NULL;

	}

	unlock_mount_hash();

	namespace_unlock();

	if (ns)

		free_mnt_ns(ns);

}
@@ -2081,6 +2087,10 @@ static int attach_recursive_mnt(struct mount *source_mnt, 
		attach_mnt(source_mnt, dest_mnt, dest_mp);

		touch_mnt_namespace(source_mnt->mnt_ns);

	} else {

		if (source_mnt->mnt_ns) {

			/* move from anon - the caller will destroy */

			list_del_init(&source_mnt->mnt_ns->list);

		}

		mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);

		commit_tree(source_mnt);

	}
@@ -2539,13 +2549,37 @@ static inline int tree_contains_unbindable(struct mount *mnt) 
	return 0;

}



/*

 * Check that there aren't references to earlier/same mount namespaces in the

 * specified subtree.  Such references can act as pins for mount namespaces

 * that aren't checked by the mount-cycle checking code, thereby allowing

 * cycles to be made.

 */

static bool check_for_nsfs_mounts(struct mount *subtree)

{

	struct mount *p;

	bool ret = false;



	lock_mount_hash();

	for (p = subtree; p; p = next_mnt(p, subtree))

		if (mnt_ns_loop(p->mnt.mnt_root))

			goto out;



	ret = true;

out:

	unlock_mount_hash();

	return ret;

}



static int do_move_mount(struct path *old_path, struct path *new_path)

{

	struct path parent_path = {.mnt = NULL, .dentry = NULL};

	struct mnt_namespace *ns;

	struct mount *p;

	struct mount *old;

	struct mountpoint *mp;

	int err;

	bool attached;



	mp = lock_mount(new_path);

	if (IS_ERR(mp))
@@ -2553,12 +2587,19 @@ static int do_move_mount(struct path *old_path, struct path *new_path) 


	old = real_mount(old_path->mnt);

	p = real_mount(new_path->mnt);

	attached = mnt_has_parent(old);

	ns = old->mnt_ns;



	err = -EINVAL;

	if (!check_mnt(p) || !check_mnt(old))

	/* The mountpoint must be in our namespace. */

	if (!check_mnt(p))

		goto out;



	/* The thing moved should be either ours or completely unattached. */

	if (attached && !check_mnt(old))

		goto out;



	if (!mnt_has_parent(old))

	if (!attached && !is_anon_ns(ns))

		goto out;



	if (old->mnt.mnt_flags & MNT_LOCKED)
@@ -2573,7 +2614,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path) 
	/*

	 * Don't move a mount residing in a shared parent.

	 */

	if (IS_MNT_SHARED(old->mnt_parent))

	if (attached && IS_MNT_SHARED(old->mnt_parent))

		goto out;

	/*

	 * Don't move a mount tree containing unbindable mounts to a destination
@@ -2582,12 +2623,14 @@ static int do_move_mount(struct path *old_path, struct path *new_path) 
	if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))

		goto out;

	err = -ELOOP;

	if (!check_for_nsfs_mounts(old))

		goto out;

	for (; mnt_has_parent(p); p = p->mnt_parent)

		if (p == old)

			goto out;



	err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp,

				   &parent_path);

				   attached ? &parent_path : NULL);

	if (err)

		goto out;
@@ -2596,8 +2639,11 @@ static int do_move_mount(struct path *old_path, struct path *new_path) 
	list_del_init(&old->mnt_expire);

out:

	unlock_mount(mp);

	if (!err)

	if (!err) {

		path_put(&parent_path);

		if (!attached)

			free_mnt_ns(ns);

	}

	return err;

}
@@ -3289,6 +3335,8 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name, 


/*

 * Move a mount from one place to another.

 * In combination with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be

 * used to copy a mount subtree.

 *

 * Note the flags value is a combination of MOVE_MOUNT_* flags.

 */

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