packets: Re-calculate IPv6 checksum only for first frag upon modify.

In case of modifying an IPv6 packet src/dst address the L4 checksum
should be recalculated only for the first frag.  Currently it's done
for all frags, leading to incorrect reassembled packet checksum.
Fix it by adding a new flag to recalculate the checksum only for the
first frag.

Fixes: bc7a5acdff08 ("datapath: add ipv6 'set' action")
Signed-off-by: Salem Sol <salems@nvidia.com>
Acked-by: Mike Pattrick <mkp@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

2 files changed, 43 insertions, 4 deletions

diff --git a/lib/packets.c b/lib/packets.c
index 9d7cc5024..4f9091e52 100644
--- a/lib/packets.c
+++ b/lib/packets.c
@@ -1010,7 +1010,7 @@ packet_set_ipv4_addr(struct dp_packet *packet,
  *
  * This function assumes that L3 and L4 offsets are set in the packet. */
 static bool
-packet_rh_present(struct dp_packet *packet, uint8_t *nexthdr)
+packet_rh_present(struct dp_packet *packet, uint8_t *nexthdr, bool *first_frag)
 {
     const struct ovs_16aligned_ip6_hdr *nh;
     size_t len;
@@ -1060,6 +1060,8 @@ packet_rh_present(struct dp_packet *packet, uint8_t *nexthdr)
             const struct ovs_16aligned_ip6_frag *frag_hdr
                 = ALIGNED_CAST(struct ovs_16aligned_ip6_frag *, data);
 
+            *first_frag = !(frag_hdr->ip6f_offlg & IP6F_OFF_MASK) &&
+                           (frag_hdr->ip6f_offlg & IP6F_MORE_FRAG);
             *nexthdr = frag_hdr->ip6f_nxt;
             len = sizeof *frag_hdr;
         } else if (*nexthdr == IPPROTO_ROUTING) {
@@ -1190,18 +1192,20 @@ packet_set_ipv6(struct dp_packet *packet, const struct in6_addr *src,
                 uint8_t key_hl)
 {
     struct ovs_16aligned_ip6_hdr *nh = dp_packet_l3(packet);
+    bool recalc_csum = true;
     uint8_t proto = 0;
     bool rh_present;
 
-    rh_present = packet_rh_present(packet, &proto);
+    rh_present = packet_rh_present(packet, &proto, &recalc_csum);
 
     if (memcmp(&nh->ip6_src, src, sizeof(ovs_be32[4]))) {
-        packet_set_ipv6_addr(packet, proto, nh->ip6_src.be32, src, true);
+        packet_set_ipv6_addr(packet, proto, nh->ip6_src.be32,
+                             src, recalc_csum);
     }
 
     if (memcmp(&nh->ip6_dst, dst, sizeof(ovs_be32[4]))) {
         packet_set_ipv6_addr(packet, proto, nh->ip6_dst.be32, dst,
-                             !rh_present);
+                             !rh_present && recalc_csum);
     }
 
     packet_set_ipv6_tc(&nh->ip6_flow, key_tc);
diff --git a/tests/system-traffic.at b/tests/system-traffic.at
index 4165b0a96..b53e279a9 100644
--- a/tests/system-traffic.at
+++ b/tests/system-traffic.at
@@ -192,6 +192,41 @@ NS_CHECK_EXEC([at_ns0], [ping6 -s 3200 -q -c 3 -i 0.3 -w 2 fc00:1::2 | FORMAT_PI
 OVS_TRAFFIC_VSWITCHD_STOP
 AT_CLEANUP
 
+AT_SETUP([datapath - ping6 between two ports with header modify])
+OVS_TRAFFIC_VSWITCHD_START()
+
+AT_CHECK([ovs-ofctl add-flow br0 "actions=normal"])
+
+ADD_NAMESPACES(at_ns0, at_ns1)
+
+ADD_VETH(p0, at_ns0, br0, "fc00::1/96", e4:11:22:33:44:55)
+ADD_VETH(p1, at_ns1, br0, "fc00::2/96", e4:11:22:33:44:54)
+NS_CHECK_EXEC([at_ns0], [ip -6 neigh add fc00::3 lladdr e4:11:22:33:44:54 dev p0])
+NS_CHECK_EXEC([at_ns0], [ip -6 neigh add fc00::2 lladdr e4:11:22:33:44:54 dev p0])
+NS_CHECK_EXEC([at_ns0], [ip -6 neigh add fc00::1 lladdr e4:11:22:33:44:55 dev p0])
+
+dnl Linux seems to take a little time to get its IPv6 stack in order. Without
+dnl waiting, we get occasional failures due to the following error:
+dnl "connect: Cannot assign requested address"
+OVS_WAIT_UNTIL([ip netns exec at_ns0 ping6 -c 1 fc00::2])
+
+AT_CHECK([ovs-ofctl del-flows -OOpenFlow15 br0])
+AT_CHECK([ovs-ofctl add-flow -OOpenFlow15 br0 in_port=ovs-p0,ipv6,ipv6_dst=fc00::3,ipv6_src=fc00::1,actions=set_field:fc00::2-\>ipv6_dst,ovs-p1])
+AT_CHECK([ovs-ofctl add-flow -OOpenFlow15 br0 in_port=ovs-p1,ipv6,ipv6_dst=fc00::1,ipv6_src=fc00::2,actions=set_field:fc00::3-\>ipv6_src,ovs-p0])
+
+NS_CHECK_EXEC([at_ns0], [ping6 -q -c 3 -i 0.3 -w 2 fc00::3 | FORMAT_PING], [0], [dnl
+3 packets transmitted, 3 received, 0% packet loss, time 0ms
+])
+NS_CHECK_EXEC([at_ns0], [ping6 -s 1600 -q -c 3 -i 0.3 -w 2 fc00::3 | FORMAT_PING], [0], [dnl
+3 packets transmitted, 3 received, 0% packet loss, time 0ms
+])
+NS_CHECK_EXEC([at_ns0], [ping6 -s 3200 -q -c 3 -i 0.3 -w 2 fc00::3 | FORMAT_PING], [0], [dnl
+3 packets transmitted, 3 received, 0% packet loss, time 0ms
+])
+
+OVS_TRAFFIC_VSWITCHD_STOP
+AT_CLEANUP
+
 AT_SETUP([datapath - ping over bond])
 OVS_TRAFFIC_VSWITCHD_START()