We forget to release the reference of tun device in tun_recvmsg.
bug introduced in commit 
54f968d6efdbf7dec36faa44fc11f01b0e4d1990
(tuntap: move socket to tun_file)
Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 
        if (!tun)
                return -EBADFD;
 
-       if (flags & ~(MSG_DONTWAIT|MSG_TRUNC))
-               return -EINVAL;
+       if (flags & ~(MSG_DONTWAIT|MSG_TRUNC)) {
+               ret = -EINVAL;
+               goto out;
+       }
        ret = tun_do_read(tun, tfile, iocb, m->msg_iov, total_len,
                          flags & MSG_DONTWAIT);
        if (ret > total_len) {
                m->msg_flags |= MSG_TRUNC;
                ret = flags & MSG_TRUNC ? ret : total_len;
        }
+out:
        tun_put(tun);
        return ret;
 }