From dc6a664089f10eab0fb36b6e4f705022210191d2 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sun, 1 Jun 2025 20:11:06 -0400 Subject: [PATCH] clone_private_mnt(): make sure that caller has CAP_SYS_ADMIN in the right userns commit c28f922c9dcee0e4876a2c095939d77fe7e15116 upstream. What we want is to verify there is that clone won't expose something hidden by a mount we wouldn't be able to undo. "Wouldn't be able to undo" may be a result of MNT_LOCKED on a child, but it may also come from lacking admin rights in the userns of the namespace mount belongs to. clone_private_mnt() checks the former, but not the latter. There's a number of rather confusing CAP_SYS_ADMIN checks in various userns during the mount, especially with the new mount API; they serve different purposes and in case of clone_private_mnt() they usually, but not always end up covering the missing check mentioned above. Reviewed-by: Christian Brauner Reported-by: "Orlando, Noah" Fixes: 427215d85e8d ("ovl: prevent private clone if bind mount is not allowed") Signed-off-by: Al Viro [ merge conflict resolution: clone_private_mount() was reworked in db04662e2f4f ("fs: allow detached mounts in clone_private_mount()"). Tweak the relevant ns_capable check so that it works on older kernels ] Signed-off-by: Noah Orlando Signed-off-by: Greg Kroah-Hartman --- fs/namespace.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index cebcb9fa2acc..6a9c53c800c4 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2110,6 +2110,11 @@ struct vfsmount *clone_private_mount(const struct path *path) if (!check_mnt(old_mnt)) goto invalid; + if (!ns_capable(old_mnt->mnt_ns->user_ns, CAP_SYS_ADMIN)) { + up_read(&namespace_sem); + return ERR_PTR(-EPERM); + } + if (has_locked_children(old_mnt, path->dentry)) goto invalid;