6lowpan: 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.

Signed-off-by: Tony Cheneau <tony.cheneau@amnesiak.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ieee802154/6lowpan.c b/net/ieee802154/6lowpan.c
index 6871ec1b30f8..416a54d31fb2 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;