fs: only copy to userspace on success in listmount()

Avoid copying when we failed to, or didn't have any mounts to list.

Fixes: cb54ef4f050e ("fs: don't copy to userspace under namespace semaphore") # mainline only
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index c53a0ee748c6faea48754b9198ac95ee2ebf0e0e..f44e5448c8a0d696907cc7c943685852e3a0970f 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5401,6 +5401,8 @@ SYSCALL_DEFINE4(listmount, const struct mnt_id_req __user *, req,
        scoped_guard(rwsem_read, &namespace_sem)
                ret = do_listmount(ns, kreq.mnt_id, kreq.param, kmnt_ids,
                                   nr_mnt_ids, (flags & LISTMOUNT_REVERSE));
+       if (ret <= 0)
+               return ret;
 
        if (copy_to_user(mnt_ids, kmnt_ids, ret * sizeof(*mnt_ids)))
                return -EFAULT;