[PATCH net-next 1/4] 6lowpan: Fix in UDP uncompression function when a null pointer gets dereferenced

[Tony Cheneau <tony.cheneauh@amnesiak.org>]

When a UDP packet gets fragmented, a crash will occur during
reassembly.
skb->transport_header is not set during earlier period of fragment
reassembly. As a consequence, calll to udp_hdr() return NULL and uh
(which is NULL) gets dereferenced without much test.
I will post a patch later that will set skb->transport_header
 correctly in lowpan_process_data(), so that
lowpan_uncompress_udp_header() behave as intended.
---
 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 32eb417..a52e795 100644
--- a/net/ieee802154/6lowpan.c
+++ b/net/ieee802154/6lowpan.c
@@ -317,6 +317,9 @@ lowpan_uncompress_udp_header(struct sk_buff *skb)
 {
 	struct udphdr *uh = udp_hdr(skb);
 	u8 tmp;
+	
+	if (!uh)
+		goto err;
 
 	tmp = lowpan_fetch_skb_u8(skb);
 
-- 
1.7.3.4