7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Brauner commit 08f4288a37ef4b3d19b4a9599ec3048219cac828 upstream. When mount_setattr() changes the propagation type to MS_SHARED do_mount_setattr() takes namespace_sem and calls invent_group_ids() which walks the whole target tree with next_mnt() and allocates a peer group id for every mount that doesn't have one. Whether the caller may touch the target at all is only checked afterwards under mount_lock. If it may not, cleanup_group_ids() walks the tree a second time on the way out to free the ids again. A detached tree that a file descriptor keeps alive, a mount in another mount namespace or a mount below the root of an anonymous mount namespace does a bunch of allocation work that is completely useless because it will fail and revert right after. Do the right thing and check the target right after taking namespace_sem instead. A mount leaves its namespace only under namespace_sem so the mount stays stable. The check under mount_lock stays for the case where no propagation change is requested and namespace_sem isn't taken. Callers get the same EINVAL as before. Fixes: 2a1867219c7b ("fs: add mount_setattr()") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260926-work-mount-fixes-2-v1-5-f357abf3d17b@kernel.org Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman --- fs/namespace.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/fs/namespace.c +++ b/fs/namespace.c @@ -4957,6 +4957,11 @@ static int do_mount_setattr(const struct * propagation. */ namespace_lock(); + /* invent_group_ids() walks the tree, only walk a mounted one */ + if (!anon_ns_root(mnt) && !check_mnt(mnt)) { + namespace_unlock(); + return -EINVAL; + } if (kattr->propagation == MS_SHARED) { err = invent_group_ids(mnt, kattr->kflags & MOUNT_KATTR_RECURSE); if (err) { @@ -4969,6 +4974,7 @@ static int do_mount_setattr(const struct err = -EINVAL; lock_mount_hash(); + /* Checked under namespace_sem already if the propagation changes. */ if (!anon_ns_root(mnt) && !check_mnt(mnt)) goto out;