7819 IPv6 Packet and MTU bug

@@ -19,10 +19,11 @@
  * CDDL HEADER END
  */
 /*
  * Copyright (c) 1991, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 1990 Mentat Inc.
+ * Copyright 2017 OmniTI Computer Consulting, Inc. All rights reserved.
  */
 
 #include <sys/types.h>
 #include <sys/stream.h>
 #include <sys/dlpi.h>

@@ -680,11 +681,23 @@
 
         /* Caller has already pulled up everything. */
         ip6h = (ip6_t *)&icmp6[1];
         final_dst = ip_get_dst_v6(ip6h, NULL, NULL);
 
+        mtu = ntohl(icmp6->icmp6_mtu);
+        if (mtu < IPV6_MIN_MTU) {
         /*
+                 * RFC 8021 suggests to ignore messages where mtu is
+                 * less than the IPv6 minimum.
+                 */
+                ip1dbg(("Received mtu less than IPv6 "
+                    "min mtu %d: %d\n", IPV6_MIN_MTU, mtu));
+                DTRACE_PROBE1(icmp6__too__small__mtu, uint32_t, mtu);
+                return;
+        }
+
+        /*
          * For link local destinations matching simply on address is not
          * sufficient. Same link local addresses for different ILL's is
          * possible.
          */
         if (IN6_IS_ADDR_LINKSCOPE(&final_dst)) {

@@ -702,51 +715,27 @@
                             &final_dst);
                 }
                 return;
         }
 
-        mtu = ntohl(icmp6->icmp6_mtu);
-
         mutex_enter(&dce->dce_lock);
         if (dce->dce_flags & DCEF_PMTU)
                 old_max_frag = dce->dce_pmtu;
         else if (IN6_IS_ADDR_MULTICAST(&final_dst))
                 old_max_frag = ill->ill_mc_mtu;
         else
                 old_max_frag = ill->ill_mtu;
 
-        if (mtu < IPV6_MIN_MTU) {
-                ip1dbg(("Received mtu less than IPv6 "
-                    "min mtu %d: %d\n", IPV6_MIN_MTU, mtu));
-                mtu = IPV6_MIN_MTU;
-                /*
-                 * If an mtu less than IPv6 min mtu is received,
-                 * we must include a fragment header in
-                 * subsequent packets.
-                 */
-                dce->dce_flags |= DCEF_TOO_SMALL_PMTU;
-        } else {
-                dce->dce_flags &= ~DCEF_TOO_SMALL_PMTU;
-        }
         ip1dbg(("Received mtu from router: %d\n", mtu));
+        DTRACE_PROBE1(icmp6__received__mtu, uint32_t, mtu);
         dce->dce_pmtu = MIN(old_max_frag, mtu);
-
-        /* Prepare to send the new max frag size for the ULP. */
-        if (dce->dce_flags & DCEF_TOO_SMALL_PMTU) {
-                /*
-                 * If we need a fragment header in every packet
-                 * (above case or multirouting), make sure the
-                 * ULP takes it into account when computing the
-                 * payload size.
-                 */
-                icmp6->icmp6_mtu = htonl(dce->dce_pmtu - sizeof (ip6_frag_t));
-        } else {
                 icmp6->icmp6_mtu = htonl(dce->dce_pmtu);
-        }
+
         /* We now have a PMTU for sure */
         dce->dce_flags |= DCEF_PMTU;
         dce->dce_last_change_time = TICK_TO_SEC(ddi_get_lbolt64());
+
         mutex_exit(&dce->dce_lock);
         /*
          * After dropping the lock the new value is visible to everyone.
          * Then we bump the generation number so any cached values reinspect
          * the dce_t.