Unverified Commit 9ed72af4 authored by Christian Brauner's avatar Christian Brauner
Browse files

fs: add may_copy_tree() 

Add a helper that verifies whether a caller may copy a given mount tree.

Link: https://lore.kernel.org/r/20250221-brauner-open_tree-v1-5-dbcfcb98c676@kernel.org


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent b73ec10a

fs/namespace.c

+37 −7
Original line number Diff line number Diff line
@@ -2808,6 +2808,41 @@ static int do_change_type(struct path *path, int ms_flags) 
	return err;

}



/* may_copy_tree() - check if a mount tree can be copied

 * @path: path to the mount tree to be copied

 *

 * This helper checks if the caller may copy the mount tree starting

 * from @path->mnt. The caller may copy the mount tree under the

 * following circumstances:

 *

 * (1) The caller is located in the mount namespace of the mount tree.

 *     This also implies that the mount does not belong to an anonymous

 *     mount namespace.

 * (2) The caller tries to copy an nfs mount referring to a mount

 *     namespace, i.e., the caller is trying to copy a mount namespace

 *     entry from nsfs.

 * (3) The caller tries to copy a pidfs mount referring to a pidfd.

 *

 * Returns true if the mount tree can be copied, false otherwise.

 */

static inline bool may_copy_tree(struct path *path)

{

	struct mount *mnt = real_mount(path->mnt);

	const struct dentry_operations *d_op;



	if (check_mnt(mnt))

		return true;



	d_op = path->dentry->d_op;

	if (d_op == &ns_dentry_operations)

		return true;



	if (d_op == &pidfs_dentry_operations)

		return true;



	return false;

}



static struct mount *__do_loopback(struct path *old_path, int recurse)

{

	struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt);
@@ -2815,13 +2850,8 @@ static struct mount *__do_loopback(struct path *old_path, int recurse) 
	if (IS_MNT_UNBINDABLE(old))

		return mnt;



	if (!check_mnt(old)) {

		const struct dentry_operations *d_op = old_path->dentry->d_op;



		if (d_op != &ns_dentry_operations &&

		    d_op != &pidfs_dentry_operations)

	if (!may_copy_tree(old_path))

		return mnt;

	}



	if (!recurse && has_locked_children(old, old_path->dentry))

		return mnt;