Certificate Transparency DNS log client

components/certificate_transparency/log_dns_client.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/certificate_transparency/log_dns_client.h"
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "base/time/time.h"
+#include "components/base32/base32.h"
+#include "crypto/sha2.h"
+#include "net/base/net_errors.h"
+#include "net/cert/merkle_audit_proof.h"
+#include "net/dns/dns_client.h"
+#include "net/dns/dns_protocol.h"
+#include "net/dns/dns_response.h"
+#include "net/dns/dns_transaction.h"
+#include "net/dns/record_parsed.h"
+#include "net/dns/record_rdata.h"
+
+namespace certificate_transparency {
+
+LogDnsClient::LogDnsClient(std::unique_ptr<net::DnsClient> dns_client,
+                           const net::BoundNetLog& net_log)
+    : dns_client_(std::move(dns_client)),
+      net_log_(net_log),
+      weak_ptr_factory_(this) {
+  CHECK(dns_client_);
+}
+
+LogDnsClient::~LogDnsClient() {}
+
+void LogDnsClient::QueryLeafIndex(base::StringPiece domain_for_log,
+                                  base::StringPiece leaf_hash,
+                                  const LeafIndexCallback& callback) {
+  if (leaf_hash.size() != crypto::kSHA256Length) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(callback, net::Error::ERR_INVALID_ARGUMENT, 0));
+    return;
+  }
+
+  std::string encoded_leaf_hash =
+      base32::Base32Encode(leaf_hash, base32::Base32EncodePolicy::OMIT_PADDING);
+  DCHECK_EQ(encoded_leaf_hash.size(), 52u);
+  std::string qname = encoded_leaf_hash;

[Eran Messeri, 2016/07/01 09:08:00]

Nit: Use StringPrintf

[Rob Percival, 2016/07/01 16:01:01]

I've opted for using std::ostringstream instead, as that gives me the same
behaviour. StringPrintf with StringPiece works differently (StringPrintf prints
"(null)" for null StringPieces, rather than an empty string).

+  qname += ".hash.";
+  domain_for_log.AppendToString(&qname);
+  qname += ".";
+
+  net::DnsTransactionFactory* factory = dns_client_->GetTransactionFactory();
+  if (factory == nullptr) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(callback, net::Error::ERR_NAME_RESOLUTION_FAILED, 0));
+    return;
+  }
+
+  net::DnsTransactionFactory::CallbackType transaction_callback = base::Bind(
+      &LogDnsClient::QueryLeafIndexComplete, weak_ptr_factory_.GetWeakPtr());
+
+  std::unique_ptr<net::DnsTransaction> dns_transaction =
+      factory->CreateTransaction(qname, net::dns_protocol::kTypeTXT,
+                                 transaction_callback, net_log_);
+
+  dns_transaction->Start();
+  leaf_index_queries_.push_back({std::move(dns_transaction), callback});
+}
+
+// The performance of this could be improved by sending all of the expected
+// queries up front. Each response can contain a maximum of 7 audit path nodes,
+// so for an audit proof of size 20, it could send 3 queries (for nodes 0-6,
+// 7-13 and 14-19) immediately. Currently, it sends only the first and then,
+// based on the number of nodes received, sends the next query. The complexity
+// of the code would increase though, as it would need to detect gaps in the
+// audit proof caused by the server not responding with the anticipated number
+// of nodes. Ownership of the proof would need to change, as it would be shared
+// between simultaneous DNS transactions.
+void LogDnsClient::QueryAuditProof(base::StringPiece domain_for_log,
+                                   uint64_t leaf_index,
+                                   uint64_t tree_size,
+                                   const AuditProofCallback& callback) {
+  if (leaf_index >= tree_size) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(callback, net::Error::ERR_INVALID_ARGUMENT, nullptr));
+    return;
+  }
+
+  std::unique_ptr<net::ct::MerkleAuditProof> proof(
+      new net::ct::MerkleAuditProof);
+  proof->leaf_index = leaf_index;
+
+  QueryAuditProofNodes(std::move(proof), domain_for_log, leaf_index, tree_size,

[Eran Messeri, 2016/07/01 09:07:59]

You could drop the leaf_index from the parameters list as it's in |proof|.
Also, add a TODO to add the tree size to the MerkleAuditProof, because a proof
that does not indicate which tree size it's for is useless.

[Rob Percival, 2016/07/01 16:01:01]

Done.

+                       0, callback);

[Eran Messeri, 2016/07/01 09:08:00]

comment what the 0 stands for, e.g.:
0 /* first proof node */

[Rob Percival, 2016/07/01 16:01:01]

Done.

+}
+
+void LogDnsClient::QueryLeafIndexComplete(net::DnsTransaction* transaction,
+                                          int net_error,
+                                          const net::DnsResponse* response) {
+  auto query_iterator =
+      std::find_if(leaf_index_queries_.begin(), leaf_index_queries_.end(),
+                   [transaction](const Query<LeafIndexCallback>& query) {
+                     return query.transaction.get() == transaction;
+                   });
+  if (query_iterator == leaf_index_queries_.end()) {
+    NOTREACHED();
+    return;
+  }
+  const Query<LeafIndexCallback> query = std::move(*query_iterator);
+  leaf_index_queries_.erase(query_iterator);
+
+  if (net_error != net::OK) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(query.callback, net_error, 0));
+    return;
+  }
+
+  if (response == nullptr) {

[Eran Messeri, 2016/07/01 09:08:00]

Nit: You could move this condition up (to line 115) and change the net_error to
be ERR_INVALID_RESPONSE  if response is null, then the check in lines 116-120
will catch that and invoke the callback with error.

[Rob Percival, 2016/07/01 16:01:01]

That could hide a more specific net_error though. I can do "if (response ==
nullptr && net_error == net::OK) net_error = net::ERR_INVALID_RESPONSE;" back at
line 115 I suppose. I guess it simplifies the flow a little.

+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(query.callback, net::ERR_INVALID_RESPONSE, 0));
+    return;
+  }
+
+  uint64_t leaf_index;
+  if (!ParseLeafIndex(*response, &leaf_index)) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(query.callback, net::ERR_DNS_MALFORMED_RESPONSE, 0));
+    return;
+  }
+
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE, base::Bind(query.callback, net::OK, leaf_index));
+}
+
+void LogDnsClient::QueryAuditProofNodes(
+    std::unique_ptr<net::ct::MerkleAuditProof> proof,
+    base::StringPiece domain_for_log,
+    uint64_t leaf_index,
+    uint64_t tree_size,
+    uint64_t node_index,
+    const AuditProofCallback& callback) {
+  CHECK(proof);
+  CHECK_LT(leaf_index, tree_size);
+  CHECK_LT(node_index,
+           net::ct::CalculateAuditPathLength(leaf_index, tree_size));
+
+  std::string qname = base::Uint64ToString(node_index);
+  qname += ".";
+  qname += base::Uint64ToString(leaf_index);
+  qname += ".";
+  qname += base::Uint64ToString(tree_size);
+  qname += ".tree.";
+  domain_for_log.AppendToString(&qname);
+  qname += ".";
+
+  net::DnsTransactionFactory* factory = dns_client_->GetTransactionFactory();
+  if (factory == nullptr) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(callback, net::Error::ERR_NAME_RESOLUTION_FAILED, nullptr));
+    return;
+  }
+
+  net::DnsTransactionFactory::CallbackType transaction_callback =
+      base::Bind(&LogDnsClient::QueryAuditProofNodesComplete,
+                 weak_ptr_factory_.GetWeakPtr(), base::Passed(std::move(proof)),
+                 domain_for_log, leaf_index, tree_size);
+
+  std::unique_ptr<net::DnsTransaction> dns_transaction =
+      factory->CreateTransaction(qname, net::dns_protocol::kTypeTXT,
+                                 transaction_callback, net_log_);
+  dns_transaction->Start();
+  audit_proof_queries_.push_back({std::move(dns_transaction), callback});
+}
+
+void LogDnsClient::QueryAuditProofNodesComplete(
+    std::unique_ptr<net::ct::MerkleAuditProof> proof,
+    base::StringPiece domain_for_log,
+    uint64_t leaf_index,
+    uint64_t tree_size,
+    net::DnsTransaction* transaction,
+    int net_error,
+    const net::DnsResponse* response) {
+  auto query_iterator =
+      std::find_if(audit_proof_queries_.begin(), audit_proof_queries_.end(),
+                   [transaction](const Query<AuditProofCallback>& query) {
+                     return query.transaction.get() == transaction;
+                   });
+
+  if (query_iterator == audit_proof_queries_.end()) {
+    NOTREACHED();
+    return;
+  }
+  const Query<AuditProofCallback> query = std::move(*query_iterator);
+  audit_proof_queries_.erase(query_iterator);
+
+  if (net_error != net::OK) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(query.callback, net_error, nullptr));
+    return;
+  }
+
+  if (response == nullptr) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(query.callback, net::ERR_INVALID_RESPONSE, nullptr));
+    return;
+  }
+
+  const uint64_t audit_path_length =
+      net::ct::CalculateAuditPathLength(leaf_index, tree_size);
+  proof->nodes.reserve(audit_path_length);
+
+  if (!ParseAuditPath(*response, proof.get())) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(query.callback, net::ERR_DNS_MALFORMED_RESPONSE, nullptr));
+    return;
+  }
+
+  const uint64_t audit_path_nodes_received = proof->nodes.size();
+  if (audit_path_nodes_received < audit_path_length) {
+    QueryAuditProofNodes(std::move(proof), domain_for_log, leaf_index,
+                         tree_size, audit_path_nodes_received, query.callback);
+    return;
+  }
+
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE,
+      base::Bind(query.callback, net::OK, base::Passed(std::move(proof))));
+}
+
+bool LogDnsClient::ParseTxtResponse(const net::DnsResponse& response,
+                                    std::string* txt) {
+  DCHECK(txt);
+
+  net::DnsRecordParser parser = response.Parser();
+  // We don't care about the creation time, since we're going to throw
+  // |parsed_record| away as soon as we've extracted the payload, so provide
+  // the "null" time.
+  auto parsed_record = net::RecordParsed::CreateFrom(&parser, base::Time());
+  if (parsed_record == nullptr)
+    return false;
+
+  auto txt_record = parsed_record->rdata<net::TxtRecordRdata>();
+  if (txt_record == nullptr)
+    return false;
+
+  *txt = base::JoinString(txt_record->texts(), "");
+  return true;
+}
+
+bool LogDnsClient::ParseLeafIndex(const net::DnsResponse& response,
+                                  uint64_t* index) {
+  std::string index_str;
+  if (!ParseTxtResponse(response, &index_str))
+    return false;
+
+  return base::StringToUint64(index_str, index);
+}
+
+bool LogDnsClient::ParseAuditPath(const net::DnsResponse& response,
+                                  net::ct::MerkleAuditProof* proof) {
+  std::string audit_path;
+  if (!ParseTxtResponse(response, &audit_path))

[Eran Messeri, 2016/07/01 09:07:59]

Also return false if the audit_path is of length 0, meaning the server has not
returned any nodes (which could lead to the code performing the same query again
and again).

[Rob Percival, 2016/07/01 16:01:01]

Done.

+    return false;
+
+  for (size_t i = 0; i < audit_path.size(); i += crypto::kSHA256Length) {
+    std::string node = audit_path.substr(i, crypto::kSHA256Length);
+
+    if (node.size() == crypto::kSHA256Length)

[Eran Messeri, 2016/07/01 09:08:00]

You could check beforehand:
if (audit_path.size() % crypto::kSHA256Length != 0)
  return false

And avoid checking each and every node.

[Rob Percival, 2016/07/01 16:01:01]

Done.

+      proof->nodes.push_back(node);
+    else
+      return false;
+  }
+
+  return true;
+}
+
+}  // namespace certificate_transparency