Commit 4954346d authored May 15, 2025 by KONDO KAZUMA(近藤　和真) Committed by Al Viro Jun 07, 2025

fs: allow clone_private_mount() for a path on real rootfs



Mounting overlayfs with a directory on real rootfs (initramfs)
as upperdir has failed with following message since commit
db04662e ("fs: allow detached mounts in clone_private_mount()").

  [    4.080134] overlayfs: failed to clone upperpath

Overlayfs mount uses clone_private_mount() to create internal mount
for the underlying layers.

The commit made clone_private_mount() reject real rootfs because
it does not have a parent mount and is in the initial mount namespace,
that is not an anonymous mount namespace.

This issue can be fixed by modifying the permission check
of clone_private_mount() following [1].

Reviewed-by: Christian Brauner <brauner@kernel.org>
Fixes: db04662e ("fs: allow detached mounts in clone_private_mount()")
Link: https://lore.kernel.org/all/20250514190252.GQ2023217@ZenIV/ [1]
Link: https://lore.kernel.org/all/20250506194849.GT2023217@ZenIV/


Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Kazuma Kondo <kazuma-kondo@nec.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent d8cc0362

fs/namespace.c

+11 −10

Original line number	Diff line number	Diff line
		@@ -2493,18 +2493,19 @@ struct vfsmount clone_private_mount(const struct path path)
		if (IS_MNT_UNBINDABLE(old_mnt))
		return ERR_PTR(-EINVAL);

		if (mnt_has_parent(old_mnt)) {
		if (!check_mnt(old_mnt))
		return ERR_PTR(-EINVAL);
		} else {
		if (!is_mounted(&old_mnt->mnt))
		return ERR_PTR(-EINVAL);

		/* Make sure this isn't something purely kernel internal. */
		if (!is_anon_ns(old_mnt->mnt_ns))
		/*
		* Make sure the source mount is acceptable.
		* Anything mounted in our mount namespace is allowed.
		* Otherwise, it must be the root of an anonymous mount
		* namespace, and we need to make sure no namespace
		* loops get created.
		*/
		if (!check_mnt(old_mnt)) {
		if (!is_mounted(&old_mnt->mnt) \|\|
		!is_anon_ns(old_mnt->mnt_ns) \|\|
		mnt_has_parent(old_mnt))
		return ERR_PTR(-EINVAL);

		/* Make sure we don't create mount namespace loops. */
		if (!check_for_nsfs_mounts(old_mnt))
		return ERR_PTR(-EINVAL);
		}