+/*
+ * If routing headers are presend and valid, set dst to the final destination.
+ * Otherwise, set it to the IPv6 destination.
+ *
+ * This is used for UDP and TCP pseudo-header in the checksum
+ * calculation.
+ */
+static void
+ip6_finddst(netdissect_options *ndo, nd_ipv6 *dst,
+ const struct ip6_hdr *ip6)
+{
+ const u_char *cp;
+ u_int advance;
+ u_int nh;
+ const void *dst_addr;
+ const struct ip6_rthdr *dp;
+ const struct ip6_rthdr0 *dp0;
+ const struct ip6_srh *srh;
+ const u_char *p;
+ int i, len;
+
+ cp = (const u_char *)ip6;
+ advance = sizeof(struct ip6_hdr);
+ nh = GET_U_1(ip6->ip6_nxt);
+ dst_addr = (const void *)ip6->ip6_dst;
+
+ while (cp < ndo->ndo_snapend) {
+ cp += advance;
+
+ switch (nh) {
+
+ case IPPROTO_HOPOPTS:
+ case IPPROTO_DSTOPTS:
+ case IPPROTO_MOBILITY_OLD:
+ case IPPROTO_MOBILITY:
+ /*
+ * These have a header length byte, following
+ * the next header byte, giving the length of
+ * the header, in units of 8 octets, excluding
+ * the first 8 octets.
+ */
+ advance = (GET_U_1(cp + 1) + 1) << 3;
+ nh = GET_U_1(cp);
+ break;
+
+ case IPPROTO_FRAGMENT:
+ /*
+ * The byte following the next header byte is
+ * marked as reserved, and the header is always
+ * the same size.
+ */
+ advance = sizeof(struct ip6_frag);
+ nh = GET_U_1(cp);
+ break;
+
+ case IPPROTO_ROUTING:
+ /*
+ * OK, we found it.
+ */
+ dp = (const struct ip6_rthdr *)cp;
+ ND_TCHECK_SIZE(dp);
+ len = GET_U_1(dp->ip6r_len);
+ switch (GET_U_1(dp->ip6r_type)) {
+
+ case IPV6_RTHDR_TYPE_0:
+ case IPV6_RTHDR_TYPE_2: /* Mobile IPv6 ID-20 */
+ dp0 = (const struct ip6_rthdr0 *)dp;
+ if (len % 2 == 1)
+ goto trunc;
+ len >>= 1;
+ p = (const u_char *) dp0->ip6r0_addr;
+ for (i = 0; i < len; i++) {
+ ND_TCHECK_16(p);
+ dst_addr = (const void *)p;
+ p += 16;
+ }
+ break;
+ case IPV6_RTHDR_TYPE_4:
+ /* IPv6 Segment Routing Header (SRH) */
+ srh = (const struct ip6_srh *)dp;
+ if (len % 2 == 1)
+ goto trunc;
+ p = (const u_char *) srh->srh_segments;
+ /*
+ * The list of segments are encoded in the reverse order.
+ * Accordingly, the final DA is encoded in srh_segments[0]
+ */
+ ND_TCHECK_16(p);
+ dst_addr = (const void *)p;
+ break;
+
+ default:
+ break;
+ }
+
+ /*
+ * Only one routing header to a customer.
+ */
+ goto done;
+
+ case IPPROTO_AH:
+ case IPPROTO_ESP:
+ case IPPROTO_IPCOMP:
+ default:
+ /*
+ * AH and ESP are, in the RFCs that describe them,
+ * described as being "viewed as an end-to-end
+ * payload" "in the IPv6 context, so that they
+ * "should appear after hop-by-hop, routing, and
+ * fragmentation extension headers". We assume
+ * that's the case, and stop as soon as we see
+ * one. (We can't handle an ESP header in
+ * the general case anyway, as its length depends
+ * on the encryption algorithm.)
+ *
+ * IPComp is also "viewed as an end-to-end
+ * payload" "in the IPv6 context".
+ *
+ * All other protocols are assumed to be the final
+ * protocol.
+ */
+ goto done;
+ }
+ }
+
+done:
+trunc:
+ GET_CPY_BYTES(dst, dst_addr, sizeof(nd_ipv6));
+}
+
projects / tcpdump / blobdiff