net/af_iucv: drop inbound packets with invalid flags

BugLink: http://bugs.launchpad.net/bugs/1800639

Inbound packets may have any combination of flag bits set in their iucv
header. If we don't know how to handle a specific combination, drop the
skb instead of leaking it.

To clarify what error is returned in this case, replace the hard-coded
0 with the corresponding macro.
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry-picked from commit 22244099)
Signed-off-by: Frank Heimes <frank.heimes@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

net/iucv/af_iucv.c

@@ -2119,8 +2119,8 @@ static int afiucv_hs_rcv(struct sk_buff *skb, struct net_device *dev,
 	struct sock *sk;
 	struct iucv_sock *iucv;
 	struct af_iucv_trans_hdr *trans_hdr;
+	int err = NET_RX_SUCCESS;
 	char nullstring[8];
-	int err = 0;
 
 	skb_pull(skb, ETH_HLEN);
 	trans_hdr = (struct af_iucv_trans_hdr *)skb->data;
@@ -2204,7 +2204,7 @@ static int afiucv_hs_rcv(struct sk_buff *skb, struct net_device *dev,
 		err = afiucv_hs_callback_rx(sk, skb);
 		break;
 	default:
-		;
+		kfree_skb(skb);
 	}
 
 	return err;