Support translating fragmented packets.

Bug: 11542311
Change-Id: I14a20b9ac669cdb5927f6ac26147bb0109099497

1 files changed, 38 insertions, 14 deletions

diff --git a/ipv6.c b/ipv6.c
index d188e47..2e83be1 100644
--- a/ipv6.c
+++ b/ipv6.c
@@ -77,6 +77,7 @@ void log_bad_address(const char *fmt, const struct in6_addr *src, const struct i
 int ipv6_packet(clat_packet out, int pos, const char *packet, size_t len) {
   const struct ip6_hdr *ip6 = (struct ip6_hdr *) packet;
   struct iphdr *ip_targ = (struct iphdr *) out[pos].iov_base;
+  struct ip6_frag *frag_hdr = NULL;
   uint8_t protocol;
   const char *next_header;
   size_t len_left;
@@ -112,10 +113,6 @@ int ipv6_packet(clat_packet out, int pos, const char *packet, size_t len) {
   len_left = len - sizeof(struct ip6_hdr);
 
   protocol = ip6->ip6_nxt;
-  if (protocol == IPPROTO_ICMPV6) {
-    // ICMP and ICMPv6 have different protocol numbers.
-    protocol = IPPROTO_ICMP;
-  }
 
   /* Fill in the IPv4 header. We need to do this before we translate the packet because TCP and
    * UDP include parts of the IP header in the checksum. Set the length to zero because we don't
@@ -124,21 +121,48 @@ int ipv6_packet(clat_packet out, int pos, const char *packet, size_t len) {
   fill_ip_header(ip_targ, 0, protocol, ip6);
   out[pos].iov_len = sizeof(struct iphdr);
 
-  // Calculate the pseudo-header checksum.
+  // If there's a Fragment header, parse it and decide what the next header is.
+  // Do this before calculating the pseudo-header checksum because it updates the next header value.
+  if (protocol == IPPROTO_FRAGMENT) {
+    frag_hdr = (struct ip6_frag *) next_header;
+    if (len_left < sizeof(*frag_hdr)) {
+      logmsg_dbg(ANDROID_LOG_ERROR, "ipv6_packet/too short for fragment header: %d", len);
+      return 0;
+    }
+
+    next_header += sizeof(*frag_hdr);
+    len_left -= sizeof(*frag_hdr);
+
+    protocol = parse_frag_header(frag_hdr, ip_targ);
+  }
+
+  // ICMP and ICMPv6 have different protocol numbers.
+  if (protocol == IPPROTO_ICMPV6) {
+    protocol = IPPROTO_ICMP;
+    ip_targ->protocol = IPPROTO_ICMP;
+  }
+
+  /* Calculate the pseudo-header checksum.
+   * Technically, the length that is used in the pseudo-header checksum is the transport layer
+   * length, which is not the same as len_left in the case of fragmented packets. But since
+   * translation does not change the transport layer length, the checksum is unaffected.
+   */
   old_sum = ipv6_pseudo_header_checksum(ip6, len_left, protocol);
   new_sum = ipv4_pseudo_header_checksum(ip_targ, len_left);
 
-  // does not support IPv6 extension headers, this will drop any packet with them
-  if (protocol == IPPROTO_ICMP) {
-    iov_len = icmp6_packet(out, pos + 1, (const struct icmp6_hdr *) next_header, len_left);
-  } else if (ip6->ip6_nxt == IPPROTO_TCP) {
-    iov_len = tcp_packet(out, pos + 1, (const struct tcphdr *) next_header, old_sum, new_sum,
+  // Does not support IPv6 extension headers except Fragment.
+  if (frag_hdr && (frag_hdr->ip6f_offlg & IP6F_OFF_MASK)) {
+    iov_len = generic_packet(out, pos + 2, next_header, len_left);
+  } else if (protocol == IPPROTO_ICMP) {
+    iov_len = icmp6_packet(out, pos + 2, (const struct icmp6_hdr *) next_header, len_left);
+  } else if (protocol == IPPROTO_TCP) {
+    iov_len = tcp_packet(out, pos + 2, (const struct tcphdr *) next_header, old_sum, new_sum,
                          len_left);
-  } else if (ip6->ip6_nxt == IPPROTO_UDP) {
-    iov_len = udp_packet(out, pos + 1, (const struct udphdr *) next_header, old_sum, new_sum,
+  } else if (protocol == IPPROTO_UDP) {
+    iov_len = udp_packet(out, pos + 2, (const struct udphdr *) next_header, old_sum, new_sum,
                          len_left);
-  } else if (ip6->ip6_nxt == IPPROTO_GRE) {
-    iov_len = generic_packet(out, pos + 1, next_header, len_left);
+  } else if (protocol == IPPROTO_GRE) {
+    iov_len = generic_packet(out, pos + 2, next_header, len_left);
   } else {
 #if CLAT_DEBUG
     logmsg(ANDROID_LOG_ERROR, "ipv6_packet/unknown next header type: %x", ip6->ip6_nxt);