[PATCH net-next 4/6] 6lowpan: add udp warning for elided checksum

[Alexander Aring <alex.aring-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Bit 5 of "UDP LOWPAN_NHC Format" indicate that the checksum can be elided.
The host need to calculate the udp checksum afterwards but this isn't
supported right now.

See:
http://tools.ietf.org/html/rfc6282#section-4.3.3
Signed-off-by: Alexander Aring <alex.aring-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 net/ieee802154/6lowpan.c | 11 ++++++++---
 net/ieee802154/6lowpan.h |  1 +
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/ieee802154/6lowpan.c b/net/ieee802154/6lowpan.c
index 616f2f6..59678da 100644
--- a/net/ieee802154/6lowpan.c
+++ b/net/ieee802154/6lowpan.c
@@ -448,9 +448,14 @@ lowpan_uncompress_udp_header(struct sk_buff *skb, struct udphdr *uh)
 		pr_debug("uncompressed UDP ports: src = %d, dst = %d\n",
 			 ntohs(uh->source), ntohs(uh->dest));
 
-		/* copy checksum */
-		memcpy(&uh->check, &skb->data[0], 2);
-		skb_pull(skb, 2);
+		/* checksum */
+		if (tmp & LOWPAN_NHC_UDP_CS_C) {
+			pr_debug("checksum elided currently not supported");
+			goto err;
+		} else {
+			memcpy(&uh->check, &skb->data[0], 2);
+			skb_pull(skb, 2);
+		}
 
 		/*
 		 * UDP lenght needs to be infered from the lower layers
diff --git a/net/ieee802154/6lowpan.h b/net/ieee802154/6lowpan.h
index 2869c05..2bc231f 100644
--- a/net/ieee802154/6lowpan.h
+++ b/net/ieee802154/6lowpan.h
@@ -231,6 +231,7 @@
 #define LOWPAN_NHC_UDP_CS_P_10	0xF2 /* source = 0xF0 + 8bit inline,
 					dest = 16 bit inline */
 #define LOWPAN_NHC_UDP_CS_P_11	0xF3 /* source & dest = 0xF0B + 4bit inline */
+#define LOWPAN_NHC_UDP_CS_C	0x04 /* checksum elided */
 
 static inline bool lowpan_fetch_skb(struct sk_buff *skb,
 		void *data, const unsigned int len)
-- 
1.8.4.2


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