6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Brauner [ Upstream commit 08f4288a37ef4b3d19b4a9599ec3048219cac828 ] 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) [ sashal: replaced anon_ns_root() with explicit checks using is_mounted(), mnt_has_parent(), and is_anon_ns() ] Signed-off-by: Sasha Levin --- fs/namespace.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index 70f59ac913b76..c0d32896981fc 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -4535,6 +4535,13 @@ static int do_mount_setattr(struct path *path, struct mount_kattr *kattr) * propagation. */ namespace_lock(); + /* invent_group_ids() walks the tree, only walk a mounted one */ + if (!is_mounted(&mnt->mnt) || + ((mnt_has_parent(mnt) || !is_anon_ns(mnt->mnt_ns)) && + !check_mnt(mnt))) { + namespace_unlock(); + return -EINVAL; + } if (kattr->propagation == MS_SHARED) { err = invent_group_ids(mnt, kattr->recurse); if (err) { @@ -4547,6 +4554,7 @@ static int do_mount_setattr(struct path *path, struct mount_kattr *kattr) err = -EINVAL; lock_mount_hash(); + /* Checked under namespace_sem already if the propagation changes. */ /* Ensure that this isn't anything purely vfs internal. */ if (!is_mounted(&mnt->mnt)) goto out; -- 2.53.0