dns: handle large resolveAny address replies

src/cares_wrap.cc

@@ -249,6 +249,23 @@ std::vector<std::pair<std::string, int>> ParseServersCsv(const char* csv) {
   return servers;
 }
 
+int GetAnswerCountForTTLBuffer(const unsigned char* buf, int len) {
+  static constexpr int kDNSAnswerCountOffset = 6;
+  static constexpr int kAresDefaultTTLBufferLength = 256;
+  if (len <= kDNSAnswerCountOffset + 1) {
+    return kAresDefaultTTLBufferLength;
+  }
+
+  const int answer_count = (static_cast<int>(buf[kDNSAnswerCountOffset]) << 8) |
+                           static_cast<int>(buf[kDNSAnswerCountOffset + 1]);
+  return answer_count == 0 ? 1 : answer_count;
+}
+
+template <typename T>
+std::vector<T> MakeAddrTTLBuffer(const unsigned char* buf, int len) {
+  return std::vector<T>(GetAnswerCountForTTLBuffer(buf, len));
+}
+
 Maybe<int> ParseGeneralReply(Environment* env,
                              const unsigned char* buf,
                              int len,
@@ -1217,11 +1234,12 @@ Maybe<int> AnyTraits::Parse(QueryAnyWrap* wrap,
   int type, status, old_count;
 
   /* Parse A records or CNAME records */
-  ares_addrttl addrttls[256];
-  int naddrttls = arraysize(addrttls);
+  std::vector<ares_addrttl> addrttls =
+      MakeAddrTTLBuffer<ares_addrttl>(buf, len);
+  int naddrttls = static_cast<int>(addrttls.size());
 
   type = ns_t_cname_or_a;
-  if (!ParseGeneralReply(env, buf, len, &type, ret, addrttls, &naddrttls)
+  if (!ParseGeneralReply(env, buf, len, &type, ret, addrttls.data(), &naddrttls)
            .To(&status)) {
     return Nothing<int>();
   }
@@ -1294,11 +1312,13 @@ Maybe<int> AnyTraits::Parse(QueryAnyWrap* wrap,
   }
 
   /* Parse AAAA records */
-  ares_addr6ttl addr6ttls[256];
-  int naddr6ttls = arraysize(addr6ttls);
+  std::vector<ares_addr6ttl> addr6ttls =
+      MakeAddrTTLBuffer<ares_addr6ttl>(buf, len);
+  int naddr6ttls = static_cast<int>(addr6ttls.size());
 
   type = ns_t_aaaa;
-  if (!ParseGeneralReply(env, buf, len, &type, ret, addr6ttls, &naddr6ttls)
+  if (!ParseGeneralReply(
+           env, buf, len, &type, ret, addr6ttls.data(), &naddr6ttls)
            .To(&status)) {
     return Nothing<int>();
   }
@@ -1486,20 +1506,22 @@ Maybe<int> ATraits::Parse(QueryAWrap* wrap,
   HandleScope handle_scope(env->isolate());
   Context::Scope context_scope(env->context());
 
-  ares_addrttl addrttls[256];
-  int naddrttls = arraysize(addrttls), status;
+  std::vector<ares_addrttl> addrttls =
+      MakeAddrTTLBuffer<ares_addrttl>(buf, len);
+  int naddrttls = static_cast<int>(addrttls.size()), status;
   Local<Array> ret = Array::New(env->isolate());
 
   int type = ns_t_a;
-  if (!ParseGeneralReply(env, buf, len, &type, ret, addrttls, &naddrttls)
+  if (!ParseGeneralReply(env, buf, len, &type, ret, addrttls.data(), &naddrttls)
            .To(&status)) {
     return Nothing<int>();
   }
   if (status != ARES_SUCCESS) {
     return Just<int>(status);
   }
 
-  Local<Array> ttls = AddrTTLToArray<ares_addrttl>(env, addrttls, naddrttls);
+  Local<Array> ttls =
+      AddrTTLToArray<ares_addrttl>(env, addrttls.data(), naddrttls);
 
   wrap->CallOnComplete(ret, ttls);
   return Just<int>(ARES_SUCCESS);
@@ -1518,20 +1540,22 @@ Maybe<int> AaaaTraits::Parse(QueryAaaaWrap* wrap,
   HandleScope handle_scope(env->isolate());
   Context::Scope context_scope(env->context());
 
-  ares_addr6ttl addrttls[256];
-  int naddrttls = arraysize(addrttls), status;
+  std::vector<ares_addr6ttl> addrttls =
+      MakeAddrTTLBuffer<ares_addr6ttl>(buf, len);
+  int naddrttls = static_cast<int>(addrttls.size()), status;
   Local<Array> ret = Array::New(env->isolate());
 
   int type = ns_t_aaaa;
-  if (!ParseGeneralReply(env, buf, len, &type, ret, addrttls, &naddrttls)
+  if (!ParseGeneralReply(env, buf, len, &type, ret, addrttls.data(), &naddrttls)
            .To(&status)) {
     return Nothing<int>();
   }
   if (status != ARES_SUCCESS) {
     return Just<int>(status);
   }
 
-  Local<Array> ttls = AddrTTLToArray<ares_addr6ttl>(env, addrttls, naddrttls);
+  Local<Array> ttls =
+      AddrTTLToArray<ares_addr6ttl>(env, addrttls.data(), naddrttls);
 
   wrap->CallOnComplete(ret, ttls);
   return Just<int>(ARES_SUCCESS);

test/parallel/test-dns-resolveany-ttl-overflow.js

@@ -0,0 +1,69 @@
+'use strict';
+const common = require('../common');
+const dnstools = require('../common/dns');
+const assert = require('assert');
+const dgram = require('dgram');
+const dns = require('dns');
+
+const dnsPromises = dns.promises;
+
+const kRecordCount = 257;
+const kADomain = 'many-a.example.org';
+
+const server = dgram.createSocket('udp4');
+
+server.on('message', common.mustCall((msg, { address, port }) => {
+  const parsed = dnstools.parseDNSPacket(msg);
+  const question = parsed.questions[0];
+  const { domain } = question;
+
+  assert.strictEqual(question.type, 'ANY');
+  assert.strictEqual(domain, kADomain);
+
+  server.send(dnstools.writeDNSPacket({
+    id: parsed.id,
+    questions: parsed.questions,
+    answers: createARecords(domain),
+  }), port, address);
+}, 2));
+
+server.bind(0, common.mustCall(async () => {
+  const { port } = server.address();
+  const callbackResolver = new dns.Resolver({ timeout: 1000, tries: 1 });
+  const promiseResolver = new dnsPromises.Resolver({ timeout: 1000, tries: 1 });
+  callbackResolver.setServers([`127.0.0.1:${port}`]);
+  promiseResolver.setServers([`127.0.0.1:${port}`]);
+
+  validateRecords(await promiseResolver.resolveAny(kADomain), 'A');
+  validateRecords(await resolveAny(callbackResolver, kADomain), 'A');
+
+  server.close();
+}));
+
+function createARecords(domain) {
+  return Array.from({ length: kRecordCount }, (_, i) => ({
+    type: 'A',
+    address: `10.0.${i >> 8}.${i & 0xff}`,
+    ttl: 60 + i,
+    domain,
+  }));
+}
+
+function resolveAny(resolver, domain) {
+  return new Promise((resolve) => {
+    resolver.resolveAny(domain, common.mustSucceed(resolve));
+  });
+}
+
+function validateRecords(records, type) {
+  assert.strictEqual(records.length, kRecordCount);
+  for (const record of records) {
+    assert.strictEqual(record.type, type);
+  }
+
+  assert.strictEqual(records[0].ttl, 60);
+  assert.strictEqual(records[255].ttl, 315);
+  assert.strictEqual(records[256].ttl, 316);
+  assert.strictEqual(records[0].address, '10.0.0.0');
+  assert.strictEqual(records[256].address, '10.0.1.0');
+}