[PATCH bluetooth-next 2/6] bluetooth: 6lowpan: use lowpan dispatch helpers

[Alexander Aring <alex.aring@gmail.com>]

This patch adds a check if the dataroom of skb contains a dispatch value
by checking if skb->len != 0. This patch also change the dispatch
evaluation by the recently introduced helpers for checking the common
6LoWPAN dispatch values for IPv6 and IPHC header.

There was also a forgotten else branch which should drop the packet if
no matching dispatch is available.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
---
Jukka,

there seems something wrong or I don't get it. There is a skb_share_check but
inside the lowpan_is_iphc branch there is a skb_clone again. From my
understanding skb_share_check will check if the skb (structure) is used
somewhere else by looking at some refcounts, if yes then clone it.

So after that the skb is always a clone, which means the skb (structure only)
is not used somewhere else. Also IPHC will manipulate the skb (buffer) as well,
so we need somewhere to be sure that the buffer isn't shared. There exists a
function "skb_unshare" which is identically like skb_share_check just for the
buffer.

It could be that you ensure that the buffer is not shared somewhere else. Anyway
I think the solution with checking the "refcounts" is a very low cost operation.

btw:
In case of IPv6 dispatch this is something else, because we move pointers there
only (adjust skb->headroom with skb->data), not manipulate the buffer, so clone
is enough there.

 net/bluetooth/6lowpan.c | 57 +++++++++++++++++++++++--------------------------
 1 file changed, 27 insertions(+), 30 deletions(-)

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index db73b8a..665bf38 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -314,15 +314,17 @@ static int recv_pkt(struct sk_buff *skb, struct net_device *dev,
 	if (!netif_running(dev))
 		goto drop;
 
-	if (dev->type != ARPHRD_6LOWPAN)
+	if (dev->type != ARPHRD_6LOWPAN || !skb->len)
 		goto drop;
 
+	skb_reset_network_header(skb);
+
 	skb = skb_share_check(skb, GFP_ATOMIC);
 	if (!skb)
 		goto drop;
 
 	/* check that it's our buffer */
-	if (skb->data[0] == LOWPAN_DISPATCH_IPV6) {
+	if (lowpan_is_ipv6(*skb_network_header(skb))) {
 		/* Copy the packet so that the IPv6 header is
 		 * properly aligned.
 		 */
@@ -334,7 +336,6 @@ static int recv_pkt(struct sk_buff *skb, struct net_device *dev,
 		local_skb->protocol = htons(ETH_P_IPV6);
 		local_skb->pkt_type = PACKET_HOST;
 
-		skb_reset_network_header(local_skb);
 		skb_set_transport_header(local_skb, sizeof(struct ipv6hdr));
 
 		if (give_skb_to_upper(local_skb, dev) != NET_RX_SUCCESS) {
@@ -347,38 +348,34 @@ static int recv_pkt(struct sk_buff *skb, struct net_device *dev,
 
 		consume_skb(local_skb);
 		consume_skb(skb);
-	} else {
-		switch (skb->data[0] & 0xe0) {
-		case LOWPAN_DISPATCH_IPHC:	/* ipv6 datagram */
-			local_skb = skb_clone(skb, GFP_ATOMIC);
-			if (!local_skb)
-				goto drop;
+	} else if (lowpan_is_iphc(*skb_network_header(skb))) {
+		local_skb = skb_clone(skb, GFP_ATOMIC);
+		if (!local_skb)
+			goto drop;
 
-			ret = iphc_decompress(local_skb, dev, chan);
-			if (ret < 0) {
-				kfree_skb(local_skb);
-				goto drop;
-			}
+		ret = iphc_decompress(local_skb, dev, chan);
+		if (ret < 0) {
+			kfree_skb(local_skb);
+			goto drop;
+		}
 
-			local_skb->protocol = htons(ETH_P_IPV6);
-			local_skb->pkt_type = PACKET_HOST;
-			local_skb->dev = dev;
+		local_skb->protocol = htons(ETH_P_IPV6);
+		local_skb->pkt_type = PACKET_HOST;
+		local_skb->dev = dev;
 
-			if (give_skb_to_upper(local_skb, dev)
-					!= NET_RX_SUCCESS) {
-				kfree_skb(local_skb);
-				goto drop;
-			}
+		if (give_skb_to_upper(local_skb, dev)
+				!= NET_RX_SUCCESS) {
+			kfree_skb(local_skb);
+			goto drop;
+		}
 
-			dev->stats.rx_bytes += skb->len;
-			dev->stats.rx_packets++;
+		dev->stats.rx_bytes += skb->len;
+		dev->stats.rx_packets++;
 
-			consume_skb(local_skb);
-			consume_skb(skb);
-			break;
-		default:
-			break;
-		}
+		consume_skb(local_skb);
+		consume_skb(skb);
+	} else {
+		goto drop;
 	}
 
 	return NET_RX_SUCCESS;
-- 
2.6.1