Mounting overlayfs with a directory on real rootfs (initramfs)
as upperdir has failed with following message since commit
db04662e2f4f ("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].
Fixes: db04662e2f4f ("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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Kazuma Kondo <kazuma-kondo@xxxxxxx>
---
Changes in v2:
- Rewrite a code following [1].
- Add a comment for a condition.
- Link to v1: https://lore.kernel.org/all/20250514002650.118278-1-kazuma-kondo@xxxxxxx/
---
fs/namespace.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 1b466c54a357..306d144d691b 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2482,18 +2482,19 @@ 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);
}
--
2.49.0
