dns: handle multiple replies for single requests

The world is a mess. A single DNS request may yield multiple, subtly
different responses; all with the same DNS protocol-level ID.

Last response wins in terms of what ends up in the cache.

First response wins in terms of the response sent to the client. Hard
to do otherwise since we have no clue that more than one answer will
be forthcoming.

Type: fix
Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: I3175a40eb1fea237048d16b852a430f5ab51eaef

1 files changed, 74 insertions, 50 deletions

diff --git a/src/vnet/dns/dns.c b/src/vnet/dns/dns.c
index 3285bedc903..eac95450485 100644
--- a/src/vnet/dns/dns.c
+++ b/src/vnet/dns/dns.c
@@ -248,7 +248,8 @@ vnet_dns_send_dns4_request (dns_main_t * dm,
   fib_index = fib_table_find (prefix.fp_proto, 0 /* default VRF for now */ );
   if (fib_index == (u32) ~ 0)
     {
-      clib_warning ("no fib table");
+      if (0)
+	clib_warning ("no fib table");
       return;
     }
 
@@ -257,7 +258,8 @@ vnet_dns_send_dns4_request (dns_main_t * dm,
   /* Couldn't find route to destination. Bail out. */
   if (fei == FIB_NODE_INDEX_INVALID)
     {
-      clib_warning ("no route to DNS server");
+      if (0)
+	clib_warning ("no route to DNS server");
       return;
     }
 
@@ -265,9 +267,10 @@ vnet_dns_send_dns4_request (dns_main_t * dm,
 
   if (sw_if_index == ~0)
     {
-      clib_warning
-	("route to %U exists, fei %d, get_resolving_interface returned"
-	 " ~0", format_ip4_address, &prefix.fp_addr, fei);
+      if (0)
+	clib_warning
+	  ("route to %U exists, fei %d, get_resolving_interface returned"
+	   " ~0", format_ip4_address, &prefix.fp_addr, fei);
       return;
     }
 
@@ -365,7 +368,8 @@ vnet_dns_send_dns6_request (dns_main_t * dm,
   fib_index = fib_table_find (prefix.fp_proto, 0 /* default VRF for now */ );
   if (fib_index == (u32) ~ 0)
     {
-      clib_warning ("no fib table");
+      if (0)
+	clib_warning ("no fib table");
       return;
     }
 
@@ -1061,6 +1065,7 @@ vnet_dns_cname_indirection_nolock (dns_main_t * dm, u32 ep_index, u8 * reply)
 	goto found_last_request;
       }
   clib_warning ("pool elt %d supposedly pending, but not found...", ep_index);
+  return -1;
 
 found_last_request:
 
@@ -2206,46 +2211,51 @@ format_dns_cache (u8 * s, va_list * args)
       return s;
     }
 
-  /* *INDENT-OFF* */
-  pool_foreach (ep, dm->entries,
-  ({
-    if (ep->flags & DNS_CACHE_ENTRY_FLAG_VALID)
-      {
-        ASSERT (ep->dns_response);
-        if (ep->flags & DNS_CACHE_ENTRY_FLAG_STATIC)
-          ss = "[S] ";
-        else
-          ss = "    ";
+  s = format (s, "DNS cache contains %d entries\n", pool_elts (dm->entries));
 
-        if (verbose < 2 && ep->flags & DNS_CACHE_ENTRY_FLAG_CNAME)
-          s = format (s, "%s%s -> %s", ss, ep->name, ep->cname);
-        else
-          s = format (s, "%s%s -> %U", ss, ep->name,
-                      format_dns_reply,
-                      ep->dns_response,
-                      verbose);
-        if (!(ep->flags & DNS_CACHE_ENTRY_FLAG_STATIC))
+  if (verbose > 0)
+    {
+      /* *INDENT-OFF* */
+      pool_foreach (ep, dm->entries,
+      ({
+        if (ep->flags & DNS_CACHE_ENTRY_FLAG_VALID)
           {
-            f64 time_left = ep->expiration_time - now;
-            if (time_left > 0.0)
-              s = format (s, "  TTL left %.1f", time_left);
+            ASSERT (ep->dns_response);
+            if (ep->flags & DNS_CACHE_ENTRY_FLAG_STATIC)
+              ss = "[S] ";
             else
-              s = format (s, "  EXPIRED");
+              ss = "    ";
 
-            if (verbose > 2)
-              s = format (s, "    %d client notifications pending\n",
-                          vec_len(ep->pending_requests));
+            if (verbose < 2 && ep->flags & DNS_CACHE_ENTRY_FLAG_CNAME)
+              s = format (s, "%s%s -> %s", ss, ep->name, ep->cname);
+            else
+              s = format (s, "%s%s -> %U", ss, ep->name,
+                          format_dns_reply,
+                          ep->dns_response,
+                          verbose);
+            if (!(ep->flags & DNS_CACHE_ENTRY_FLAG_STATIC))
+              {
+                f64 time_left = ep->expiration_time - now;
+                if (time_left > 0.0)
+                  s = format (s, "  TTL left %.1f", time_left);
+                else
+                  s = format (s, "  EXPIRED");
+
+                if (verbose > 2)
+                  s = format (s, "    %d client notifications pending\n",
+                              vec_len(ep->pending_requests));
+              }
           }
-      }
-    else
-      {
-        ASSERT (ep->dns_request);
-        s = format (s, "[P] %U", format_dns_reply, ep->dns_request,
-                    verbose);
-      }
-    vec_add1 (s, '\n');
-  }));
-  /* *INDENT-ON* */
+        else
+          {
+            ASSERT (ep->dns_request);
+            s = format (s, "[P] %U", format_dns_reply, ep->dns_request,
+                        verbose);
+          }
+        vec_add1 (s, '\n');
+      }));
+      /* *INDENT-ON* */
+    }
 
   dns_cache_unlock (dm);
 
@@ -2764,6 +2774,7 @@ vnet_send_dns4_reply (dns_main_t * dm, dns_pending_request_t * pr,
   dns_rr_t *rr;
   u8 *rrptr;
   int is_fail = 0;
+  int is_recycle = (b0 != 0);
 
   ASSERT (ep && ep->dns_response);
 
@@ -2804,6 +2815,16 @@ vnet_send_dns4_reply (dns_main_t * dm, dns_pending_request_t * pr,
 	return;
       b0 = vlib_get_buffer (vm, bi);
     }
+  else
+    {
+      /* Use the buffer we were handed. Reinitialize it... */
+      vlib_buffer_t bt = { };
+      /* push/pop the reference count */
+      u8 save_ref_count = b0->ref_count;
+      vlib_buffer_copy_template (b0, &bt);
+      b0->ref_count = save_ref_count;
+      bi = vlib_get_buffer_index (vm, b0);
+    }
 
   if (b0->flags & VLIB_BUFFER_NEXT_PRESENT)
     vlib_buffer_free_one (vm, b0->next_buffer);
@@ -2817,9 +2838,6 @@ vnet_send_dns4_reply (dns_main_t * dm, dns_pending_request_t * pr,
    */
   b0->flags |= (VNET_BUFFER_F_LOCALLY_ORIGINATED
 		| VLIB_BUFFER_TOTAL_LENGTH_VALID);
-  b0->current_data = 0;
-  b0->current_length = 0;
-  b0->total_length_not_including_first_buffer = 0;
   vnet_buffer (b0)->sw_if_index[VLIB_RX] = 0;	/* "local0" */
   vnet_buffer (b0)->sw_if_index[VLIB_TX] = 0;	/* default VRF for now */
 
@@ -2971,12 +2989,18 @@ found_src_address:
   udp->checksum = 0;
   vec_free (reply);
 
-  /* Ship it to ip4_lookup */
-  f = vlib_get_frame_to_node (vm, ip4_lookup_node.index);
-  to_next = vlib_frame_vector_args (f);
-  to_next[0] = bi;
-  f->n_vectors = 1;
-  vlib_put_frame_to_node (vm, ip4_lookup_node.index, f);
+  /*
+   * Ship pkts made out of whole cloth to ip4_lookup
+   * Caller will ship recycled dns reply packets to ip4_lookup
+   */
+  if (is_recycle == 0)
+    {
+      f = vlib_get_frame_to_node (vm, ip4_lookup_node.index);
+      to_next = vlib_frame_vector_args (f);
+      to_next[0] = bi;
+      f->n_vectors = 1;
+      vlib_put_frame_to_node (vm, ip4_lookup_node.index, f);
+    }
 }
 
 /*