fs: drop peer group ids under namespace lock

When cleaning up peer group ids in the failure path we need to make sure
to hold on to the namespace lock. Otherwise another thread might just
turn the mount from a shared into a non-shared mount concurrently.

Link: https://lore.kernel.org/lkml/00000000000088694505f8132d77@google.com
Fixes: 2a1867219c7b ("fs: add mount_setattr()")
Reported-by: syzbot+8ac3859139c685c4f597@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org # 5.12+
Message-Id: <20230330-vfs-mount_setattr-propagation-fix-v1-1-37548d91533b@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index bc0f15257b49c2f00f76ba53df2af8f44c6519c0..6836e937ee613814bda7cef7c00cda14bcc17b82 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -4183,9 +4183,9 @@ out:
        unlock_mount_hash();
 
        if (kattr->propagation) {
-               namespace_unlock();
                if (err)
                        cleanup_group_ids(mnt, NULL);
+               namespace_unlock();
        }
 
        return err;