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charset="utf-8" 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 Signed-off-by: Kazuma Kondo --- 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-ko= ndo@nec.com/ --- 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 p= ath *path) if (IS_MNT_UNBINDABLE(old_mnt)) return ERR_PTR(-EINVAL); =20 - 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); =20 - /* Make sure we don't create mount namespace loops. */ if (!check_for_nsfs_mounts(old_mnt)) return ERR_PTR(-EINVAL); } --=20 2.49.0