[PATCH net-next v2 1/4] Fix null pointer dereference in UDP uncompression function

When a UDP packet gets fragmented, a crash will occur at reassembly time.
This is because skb->transport_header is not set during earlier period of fragment reassembly.
As a consequence, call to udp_hdr() return NULL and uh (which is NULL) gets
dereferenced without much test.

---
 net/ieee802154/6lowpan.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/net/ieee802154/6lowpan.c b/net/ieee802154/6lowpan.c
index f4070e5..07fa200 100644
--- a/net/ieee802154/6lowpan.c
+++ b/net/ieee802154/6lowpan.c

@@ -314,6 +314,9 @@ lowpan_uncompress_udp_header(struct sk_buff *skb)
 {
 	struct udphdr *uh = udp_hdr(skb);
 	u8 tmp;
+
+	if (!uh)
+		goto err;
 
 	if (lowpan_fetch_skb_u8(skb, &tmp))
 		goto err;

-- 
1.7.3.4