s390/qeth: guard against runt packets

Depending on a packet's type, the RX path needs to access fields in the
packet headers and thus requires a minimum packet length.
Enforce this length when building the skb.

On the other hand a single runt packet is no reason to drop the whole
RX buffer. So just skip it, and continue processing on the next packet.

Fixes: 4a71df50 ("qeth: new qeth device driver")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_core.h

@@ -480,6 +480,7 @@ struct qeth_card_stats {
 
 	u64 rx_dropped_nomem;
 	u64 rx_dropped_notsupp;
+	u64 rx_dropped_runt;
 
 	/* rtnl_link_stats64 */
 	u64 rx_packets;

drivers/s390/net/qeth_core_main.c

@@ -5063,9 +5063,9 @@ struct sk_buff *qeth_core_get_next_skb(struct qeth_card *card,
 {
 	struct qdio_buffer_element *element = *__element;
 	struct qdio_buffer *buffer = qethbuffer->buffer;
+	unsigned int headroom, linear_len;
 	int offset = *__offset;
 	bool use_rx_sg = false;
-	unsigned int headroom;
 	struct sk_buff *skb;
 	int skb_len = 0;
 	void *data_ptr;
@@ -5082,29 +5082,41 @@ struct sk_buff *qeth_core_get_next_skb(struct qeth_card *card,
 	*hdr = element->addr + offset;
 
 	offset += sizeof(struct qeth_hdr);
+	skb = NULL;
+
 	switch ((*hdr)->hdr.l2.id) {
 	case QETH_HEADER_TYPE_LAYER2:
 		skb_len = (*hdr)->hdr.l2.pkt_length;
+		linear_len = ETH_HLEN;
 		headroom = 0;
 		break;
 	case QETH_HEADER_TYPE_LAYER3:
 		skb_len = (*hdr)->hdr.l3.length;
 		if (!IS_LAYER3(card)) {
 			QETH_CARD_STAT_INC(card, rx_dropped_notsupp);
-			skb = NULL;
 			goto walk_packet;
 		}
 
+		if ((*hdr)->hdr.l3.flags & QETH_HDR_PASSTHRU) {
+			linear_len = ETH_HLEN;
+			headroom = 0;
+			break;
+		}
+
+		if ((*hdr)->hdr.l3.flags & QETH_HDR_IPV6)
+			linear_len = sizeof(struct ipv6hdr);
+		else
+			linear_len = sizeof(struct iphdr);
 		headroom = ETH_HLEN;
 		break;
 	case QETH_HEADER_TYPE_OSN:
 		skb_len = (*hdr)->hdr.osn.pdu_length;
 		if (!IS_OSN(card)) {
 			QETH_CARD_STAT_INC(card, rx_dropped_notsupp);
-			skb = NULL;
 			goto walk_packet;
 		}
 
+		linear_len = skb_len;
 		headroom = sizeof(struct qeth_hdr);
 		break;
 	default:
@@ -5117,8 +5129,10 @@ struct sk_buff *qeth_core_get_next_skb(struct qeth_card *card,
 		return NULL;
 	}
 
-	if (!skb_len)
-		return NULL;
+	if (skb_len < linear_len) {
+		QETH_CARD_STAT_INC(card, rx_dropped_runt);
+		goto walk_packet;
+	}
 
 	use_rx_sg = (card->options.cq == QETH_CQ_ENABLED) ||
 		    ((skb_len >= card->options.rx_sg_cb) &&
@@ -6268,7 +6282,8 @@ void qeth_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
 			   card->stats.rx_frame_errors +
 			   card->stats.rx_fifo_errors;
 	stats->rx_dropped = card->stats.rx_dropped_nomem +
-			    card->stats.rx_dropped_notsupp;
+			    card->stats.rx_dropped_notsupp +
+			    card->stats.rx_dropped_runt;
 	stats->multicast = card->stats.rx_multicast;
 	stats->rx_length_errors = card->stats.rx_length_errors;
 	stats->rx_frame_errors = card->stats.rx_frame_errors;

drivers/s390/net/qeth_ethtool.c

@@ -51,6 +51,7 @@ static const struct qeth_stats card_stats[] = {
 	QETH_CARD_STAT("rx0 SG page allocs", rx_sg_alloc_page),
 	QETH_CARD_STAT("rx0 dropped, no memory", rx_dropped_nomem),
 	QETH_CARD_STAT("rx0 dropped, bad format", rx_dropped_notsupp),
+	QETH_CARD_STAT("rx0 dropped, runt", rx_dropped_runt),
 };
 
 #define TXQ_STATS_LEN	ARRAY_SIZE(txq_stats)