nettrace - skip over a single hopopts or dstops ipv6 extension header

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Iad7800387e1b84587794be93d037f712ac95fa07
diff --git a/bpf_progs/netd.c b/bpf_progs/netd.c
index 41a93f4..368cfca 100644
--- a/bpf_progs/netd.c
+++ b/bpf_progs/netd.c
@@ -272,6 +272,16 @@
         (void)bpf_skb_load_bytes_net(skb, IP6_OFFSET(nexthdr), &proto, sizeof(proto), kver);
         L4_off = sizeof(struct ipv6hdr);
         ipVersion = 6;
+        // skip over a *single* HOPOPTS or DSTOPTS extension header (if present)
+        if (proto == IPPROTO_HOPOPTS || proto == IPPROTO_DSTOPTS) {
+            struct {
+                uint8_t proto, len;
+            } ext_hdr;
+            if (!bpf_skb_load_bytes_net(skb, L4_off, &ext_hdr, sizeof(ext_hdr), kver)) {
+                proto = ext_hdr.proto;
+                L4_off += (ext_hdr.len + 1) * 8;
+            }
+        }
     }
 
     uint8_t flags = 0;