Don't overwrite the destination IPv6 address for routing headers.

If we have a routing header, instead of overwriting the packet's IPv6
destination address in the packet with the final destination, so that
the next protocol's checksum routine can use it, we do as we do for
IPv4, and, in the "next protocol checksum" routine, scan the headers
looking for a routing header and, if we find one, copy the final
destination from it.

While we're at it, clean up a few things.

1 files changed, 143 insertions, 5 deletions

diff --git a/print-ip6.c b/print-ip6.c
index 45508ced..3968f333 100644
--- a/print-ip6.c
+++ b/print-ip6.c
@@ -35,10 +35,131 @@
 #include "ipproto.h"
 
 /*
+ * 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, struct in6_addr *dst,
+            const struct ip6_hdr *ip6)
+{
+	const u_char *cp;
+	int advance;
+	u_int nh;
+	const struct in6_addr *dst_addr;
+	const struct ip6_rthdr *dp;
+	const struct ip6_rthdr0 *dp0;
+	const struct in6_addr *addr;
+	int i, len;
+
+	cp = (const u_char *)ip6;
+	advance = sizeof(struct ip6_hdr);
+	nh = ip6->ip6_nxt;
+	dst_addr = &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.
+			 */
+			ND_TCHECK2(*cp, 2);
+			advance = (int)((*(cp + 1) + 1) << 3);
+			nh = *cp;
+			break;
+
+		case IPPROTO_FRAGMENT:
+			/*
+			 * The byte following the next header byte is
+			 * marked as reserved, and the header is always
+			 * the same size.
+			 */
+			ND_TCHECK2(*cp, 1);
+			advance = sizeof(struct ip6_frag);
+			nh = *cp;
+			break;
+
+		case IPPROTO_ROUTING:
+			/*
+			 * OK, we found it.
+			 */
+			dp = (const struct ip6_rthdr *)cp;
+			ND_TCHECK(*dp);
+			len = dp->ip6r_len;
+			switch (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;
+				addr = &dp0->ip6r0_addr[0];
+				for (i = 0; i < len; i++) {
+					if ((const u_char *)(addr + 1) > ndo->ndo_snapend)
+						goto trunc;
+
+					dst_addr = addr;
+					addr++;
+				}
+				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:
+	UNALIGNED_MEMCPY(dst, dst_addr, sizeof(struct in6_addr));
+}
+
+/*
  * Compute a V6-style checksum by building a pseudoheader.
  */
 int
-nextproto6_cksum(const struct ip6_hdr *ip6, const uint8_t *data,
+nextproto6_cksum(netdissect_options *ndo,
+                 const struct ip6_hdr *ip6, const uint8_t *data,
 		 u_int len, u_int covlen, u_int next_proto)
 {
         struct {
@@ -53,7 +174,26 @@ nextproto6_cksum(const struct ip6_hdr *ip6, const uint8_t *data,
         /* pseudo-header */
         memset(&ph, 0, sizeof(ph));
         UNALIGNED_MEMCPY(&ph.ph_src, &ip6->ip6_src, sizeof (struct in6_addr));
-        UNALIGNED_MEMCPY(&ph.ph_dst, &ip6->ip6_dst, sizeof (struct in6_addr));
+        switch (ip6->ip6_nxt) {
+
+        case IPPROTO_HOPOPTS:
+        case IPPROTO_DSTOPTS:
+        case IPPROTO_MOBILITY_OLD:
+        case IPPROTO_MOBILITY:
+        case IPPROTO_FRAGMENT:
+        case IPPROTO_ROUTING:
+                /*
+                 * The next header is either a routing header or a header
+                 * after which there might be a routing header, so scan
+                 * for a routing header.
+                 */
+                ip6_finddst(ndo, &ph.ph_dst, ip6);
+                break;
+
+        default:
+                UNALIGNED_MEMCPY(&ph.ph_dst, &ip6->ip6_dst, sizeof (struct in6_addr));
+                break;
+        }
         ph.ph_len = htonl(len);
         ph.ph_nxt = next_proto;
 
@@ -168,9 +308,7 @@ ip6_print(netdissect_options *ndo, const u_char *bp, u_int length)
 		case IPPROTO_MOBILITY_OLD:
 		case IPPROTO_MOBILITY:
 			/*
-			 * XXX - we don't use "advance"; the current
-			 * "Mobility Support in IPv6" draft
-			 * (draft-ietf-mobileip-ipv6-24) says that
+			 * XXX - we don't use "advance"; RFC 3775 says that
 			 * the next header field in a mobility header
 			 * should be IPPROTO_NONE, but speaks of
 			 * the possiblity of a future extension in