[PATCH net-next v3 1/3] 6lowpan: Fix null pointer dereference in UDP uncompression function

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

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.

Signed-off-by: Tony Cheneau <tony.cheneau@amnesiak.org>
---
 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..0c9f6d1 100644
--- a/net/ieee802154/6lowpan.c
+++ b/net/ieee802154/6lowpan.c
@@ -315,6 +315,9 @@ 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