ipv6: check return value of ipv6_skip_exthdr

The offset value is used in pointer math on skb->data.
Since ipv6_skip_exthdr may return -1 the pointer to uh and th
may not point to the actual udp and tcp headers and potentially
overwrite other stuff. This is why I think this should be checked.

EDIT:  added {}'s, thanks Kees

Signed-off-by: Jordy Zomer <jordy@pwning.systems>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index ed2f061b87685d6109021bd64d2029798c0ceb0f..f0bac6f7ab6bb768b12e51c937c0948e35ee5c07 100644 (file)
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -808,6 +808,12 @@ int esp6_input_done2(struct sk_buff *skb, int err)
                struct tcphdr *th;
 
                offset = ipv6_skip_exthdr(skb, offset, &nexthdr, &frag_off);
+
+               if (offset < 0) {
+                       err = -EINVAL;
+                       goto out;
+               }
+
                uh = (void *)(skb->data + offset);
                th = (void *)(skb->data + offset);
                hdr_len += offset;