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

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Mounting overlayfs with a directory on real rootfs (initramfs)
as upperdir has failed with following message since commit
db04662e2f ("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: db04662e2f ("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>
This commit is contained in:
KONDO KAZUMA(近藤　和真) 2025-05-15 12:18:30 +00:00 committed by Al Viro
parent d8cc0362f9
commit 4954346d80
1 changed files with 11 additions and 10 deletions
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21
fs/namespace.c
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@ -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))
/*
* 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 this isn't something purely kernel internal. */
if (!is_anon_ns(old_mnt->mnt_ns))
return ERR_PTR(-EINVAL);
/* Make sure we don't create mount namespace loops. */
if (!check_for_nsfs_mounts(old_mnt))
return ERR_PTR(-EINVAL);
}