Only count valid addresses when response parsing (#302)

When ares_parse_a_reply or ares_parse_aaaa_reply is called in case
where another AAAA and A responses exist, the resulting ares_addrttl
count is invalid and the structure points to gibberish.

This is a regression since 1.15.

Issue: https://github.com/c-ares/c-ares/issues/300
Fix By: Adam Majer (@AdamMajer)

ares_parse_a_reply.c

@@ -86,7 +86,10 @@ int ares_parse_a_reply(const unsigned char *abuf, int alen,
   next = ai.nodes;
   while (next)
     {
-      ++naddrs;
+      if (next->ai_family == AF_INET)
+        {
+          ++naddrs;
+        }
       next = next->ai_next;
     }
 

ares_parse_aaaa_reply.c

@@ -88,7 +88,10 @@ int ares_parse_aaaa_reply(const unsigned char *abuf, int alen,
   next = ai.nodes;
   while (next)
     {
-      ++naddrs;
+      if(next->ai_family == AF_INET6)
+        {
+          ++naddrs;
+        }
       next = next->ai_next;
     }
 

test/ares-test-parse-a.cc

@@ -11,13 +11,14 @@ TEST_F(LibraryTest, ParseAReplyOK) {
   DNSPacket pkt;
   pkt.set_qid(0x1234).set_response().set_aa()
     .add_question(new DNSQuestion("example.com", ns_t_a))
-    .add_answer(new DNSARR("example.com", 0x01020304, {2,3,4,5}));
+    .add_answer(new DNSARR("example.com", 0x01020304, {2,3,4,5}))
+    .add_answer(new DNSAaaaRR("example.com", 0x01020304, {0,0,0,0,0,0,0,0,0,0,0,0,2,3,4,5}));
   std::vector<byte> data = {
     0x12, 0x34,  // qid
     0x84, // response + query + AA + not-TC + not-RD
     0x00, // not-RA + not-Z + not-AD + not-CD + rc=NoError
     0x00, 0x01,  // num questions
-    0x00, 0x01,  // num answer RRs
+    0x00, 0x02,  // num answer RRs
     0x00, 0x00,  // num authority RRs
     0x00, 0x00,  // num additional RRs
     // Question
@@ -35,6 +36,15 @@ TEST_F(LibraryTest, ParseAReplyOK) {
     0x01, 0x02, 0x03, 0x04, // TTL
     0x00, 0x04,  // rdata length
     0x02, 0x03, 0x04, 0x05,
+    // Answer 2
+    0x07, 'e', 'x', 'a', 'm', 'p', 'l', 'e',
+    0x03, 'c', 'o', 'm',
+    0x00,
+    0x00, 0x1c,  //  RR type
+    0x00, 0x01,  //  class IN
+    0x01, 0x02, 0x03, 0x04, // TTL
+    0x00, 0x10,  // rdata length
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x03, 0x04, 0x05,
   };
   EXPECT_EQ(data, pkt.data());
   struct hostent *host = nullptr;
@@ -68,7 +78,7 @@ TEST_F(LibraryTest, ParseMalformedAReply) {
     0x84, // [2] response + query + AA + not-TC + not-RD
     0x00, // [3] not-RA + not-Z + not-AD + not-CD + rc=NoError
     0x00, 0x01,  // [4:6) num questions
-    0x00, 0x01,  // [6:8) num answer RRs
+    0x00, 0x02,  // [6:8) num answer RRs
     0x00, 0x00,  // [8:10) num authority RRs
     0x00, 0x00,  // [10:12) num additional RRs
     // Question

test/ares-test-parse-aaaa.cc

@@ -13,7 +13,8 @@ TEST_F(LibraryTest, ParseAaaaReplyOK) {
     .add_question(new DNSQuestion("example.com", ns_t_aaaa))
     .add_answer(new DNSAaaaRR("example.com", 100,
                               {0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02,
-                               0x03, 0x03, 0x03, 0x03, 0x04, 0x04, 0x04, 0x04}));
+                               0x03, 0x03, 0x03, 0x03, 0x04, 0x04, 0x04, 0x04}))
+    .add_answer(new DNSARR("example.com", 0x01020304, {2,3,4,5}));
   std::vector<byte> data = pkt.data();
   struct hostent *host = nullptr;
   struct ares_addr6ttl info[5];