net: Add fuzzer for HostResolverImpl.

net/dns/fuzzed_host_resolver.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 "net/dns/fuzzed_host_resolver.h"
+
+#include <stdint.h>
+
+#include <limits>
+#include <string>
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
+#include "base/thread_task_runner_handle.h"
+#include "net/base/address_list.h"
+#include "net/base/fuzzed_data_provider.h"
+#include "net/base/ip_address.h"
+#include "net/base/ip_endpoint.h"
+#include "net/base/net_errors.h"
+#include "net/dns/dns_client.h"
+#include "net/dns/dns_config_service.h"
+#include "net/dns/dns_hosts.h"
+
+namespace net {
+
+namespace {
+
+// HostResolverProc that returns a random set of results, and can succeed or
+// fail. Must only be run on the thread it's created on.
+class FuzzedHostResolverProc : public HostResolverProc {
+ public:
+  // Can safely be used after the destruction of |data_provider|. This can
+  // happen if a request is issued but the code never waits for the result
+  // before the test ends.
+  explicit FuzzedHostResolverProc(
+      base::WeakPtr<FuzzedDataProvider> data_provider)
+      : HostResolverProc(nullptr),
+        data_provider_(data_provider),
+        network_task_runner_(base::ThreadTaskRunnerHandle::Get()) {}
+
+  int Resolve(const std::string& host,
+              AddressFamily address_family,
+              HostResolverFlags host_resolver_flags,
+              AddressList* addrlist,
+              int* os_error) override {
+    DCHECK(network_task_runner_->BelongsToCurrentThread());
+
+    if (os_error)
+      *os_error = 0;
+
+    // If the data provider is no longer avaiable, just fail. The HostResolver
+    // has already been deleted by this point, anyways.
+    if (!data_provider_)
+      return ERR_FAILED;
+
+    AddressList result;
+
+    // Put IPv6 addresses before IPv4 ones. This code doesn't sort addresses
+    // correctly, but when sorted according to spec, IPv6 addresses are
+    // generally before IPv4 ones.
+    if (address_family == ADDRESS_FAMILY_UNSPECIFIED ||
+        address_family == ADDRESS_FAMILY_IPV6) {
+      while (data_provider_->ConsumeBool()) {
+        result.push_back(IPEndPoint(
+            IPAddress(
+                data_provider_->ConsumeUint8(), data_provider_->ConsumeUint8(),
+                data_provider_->ConsumeUint8(), data_provider_->ConsumeUint8(),
+                data_provider_->ConsumeUint8(), data_provider_->ConsumeUint8(),
+                data_provider_->ConsumeUint8(), data_provider_->ConsumeUint8(),
+                data_provider_->ConsumeUint8(), data_provider_->ConsumeUint8(),
+                data_provider_->ConsumeUint8(), data_provider_->ConsumeUint8(),
+                data_provider_->ConsumeUint8(), data_provider_->ConsumeUint8(),
+                data_provider_->ConsumeUint8(), data_provider_->ConsumeUint8()),
+            0));
+      }
+    }
+
+    if (address_family == ADDRESS_FAMILY_UNSPECIFIED ||
+        address_family == ADDRESS_FAMILY_IPV4) {
+      while (data_provider_->ConsumeBool()) {
+        result.push_back(IPEndPoint(IPAddress(data_provider_->ConsumeUint8(),
+                                              data_provider_->ConsumeUint8(),
+                                              data_provider_->ConsumeUint8(),
+                                              data_provider_->ConsumeUint8()),
+                                    0));
+      }
+    }
+
+    if (result.empty())
+      return ERR_NAME_NOT_RESOLVED;
+
+    if (host_resolver_flags & HOST_RESOLVER_CANONNAME) {
+      // Don't bother to fuzz this - almost nothing cares.
+      result.set_canonical_name("foo.com");
+    }
+
+    *addrlist = result;
+    return OK;
+  }
+
+ private:
+  ~FuzzedHostResolverProc() override {}
+
+  base::WeakPtr<FuzzedDataProvider> data_provider_;
+
+  // Just used for thread-safety checks.
+  scoped_refptr<base::SingleThreadTaskRunner> network_task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(FuzzedHostResolverProc);
+};
+
+}  // namespace
+
+FuzzedHostResolver::FuzzedHostResolver(const Options& options,
+                                       NetLog* net_log,
+                                       FuzzedDataProvider* data_provider)
+    : HostResolverImpl(options, net_log, base::ThreadTaskRunnerHandle::Get()),
+      data_provider_(data_provider),
+      socket_factory_(data_provider),
+      is_ipv6_reachable_(data_provider->ConsumeBool()),
+      net_log_(net_log),
+      data_provider_weak_factory_(data_provider) {
+  HostResolverImpl::ProcTaskParams proc_task_params(
+      new FuzzedHostResolverProc(data_provider_weak_factory_.GetWeakPtr()),
+      // Retries are only used when the original request hangs, which this class
+      // currently can't simulate.
+      0 /* max_retry_attempts */);
+  set_proc_params_for_test(proc_task_params);
+}
+
+FuzzedHostResolver::~FuzzedHostResolver() {}
+
+void FuzzedHostResolver::SetDnsClientEnabled(bool enabled) {
+  if (!enabled) {
+    HostResolverImpl::SetDnsClientEnabled(false);
+    return;
+  }
+
+  // Fuzz DNS configuration.
+
+  DnsConfig config;
+  // Determine the number of name servers. Each case deliberately falls through.
+  switch (data_provider_->ConsumeValueInRange(0, 3)) {

[Julia Tuttle, 2016/05/13 17:15:13]

It bothers me slightly that this construction keeps us from creating, for
example, { 8.8.8.8, 8.8.4.4 } as a nameserver list, and ditto for the others
below, to a lesser degree.

[mmenke, 2016/05/17 19:50:36]

Fuzzed this, and the IPs in the hosts file (And the number / type / order of
those IPs).  Still have hard-coded DNS addresses, though.

+    case 3:
+      config.nameservers.push_back(IPEndPoint(IPAddress(1, 2, 3, 6), 345));
+    case 2:
+      config.nameservers.push_back(IPEndPoint(IPAddress::IPv6Localhost(), 77));
+    case 1:
+      config.nameservers.push_back(IPEndPoint(IPAddress(1, 2, 3, 4), 53));
+    default:
+      break;
+  }
+
+  // Determine the number of suffixes to try. Each case deliberately falls
+  // through.
+  switch (data_provider_->ConsumeValueInRange(0, 3)) {
+    case 3:
+      config.search.push_back("foo.com");
+    case 2:
+      config.search.push_back("bar");
+    case 1:
+      config.search.push_back("com");
+    default:
+      break;
+  }
+
+  net::DnsHosts hosts;
+  // Fuzz hosts file. Each case deliberately falls through.
+  switch (data_provider_->ConsumeValueInRange(0, 4)) {
+    case 4:
+      config.hosts[net::DnsHostsKey("foo.com", net::ADDRESS_FAMILY_IPV4)] =
+          net::IPAddress(1, 2, 3, 4);
+    case 3:
+      config.hosts[net::DnsHostsKey("foo.com", net::ADDRESS_FAMILY_IPV6)] =
+          net::IPAddress(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16);
+    case 2:
+      config.hosts[net::DnsHostsKey("foo", net::ADDRESS_FAMILY_IPV4)] =
+          net::IPAddress(1, 2, 3, 5);
+    case 1:
+      config.hosts[net::DnsHostsKey("foo", net::ADDRESS_FAMILY_IPV4)] =
+          net::IPAddress(1, 2, 3, 4);
+    default:
+      break;
+  }
+
+  config.unhandled_options = data_provider_->ConsumeBool();
+  config.append_to_multi_label_name = data_provider_->ConsumeBool();
+  config.randomize_ports = data_provider_->ConsumeBool();
+  config.attempts = data_provider_->ConsumeValueInRange(1, 3);
+  config.ndots = data_provider_->ConsumeValueInRange(0, 3);
+
+  // Timeouts don't really work for fuzzing. Even a timeout of 0 milliseconds

[Julia Tuttle, 2016/05/13 17:15:13]

I understand that fuzzing the timeout doesn't work, but why did you pick such a
long timeout for the constant value?

[mmenke, 2016/05/17 19:50:36]

Because if it ever triggers, it causes non-determinism.  If it's 5 milliseconds,
sometimes it may trigger, sometimes it may not, depending on whatever else the
test system is doing.  If a fuzzer does one thing on input 1% of the time, and
another thing on it 99% of the time, it's not a good fuzzer - if that 1% is a
bad failure, then you can basically never repro it, which defeats the point of
recording bad input cases to debug.

+  // will be increased after the first timeout, resulting in inconsistent
+  // behavior.
+  config.timeout = base::TimeDelta::FromDays(10);
+
+  config.rotate = data_provider_->ConsumeBool();
+
+  // Doesn't currently seem to do anything.
+  config.edns0 = false;
+
+  config.use_local_ipv6 = data_provider_->ConsumeBool();
+
+  std::unique_ptr<DnsClient> dns_client = DnsClient::CreateClientForTesting(
+      net_log_, &socket_factory_,
+      base::Bind(&FuzzedDataProvider::ConsumeValueInRangeInt,
+                 base::Unretained(data_provider_)));
+  dns_client->SetConfig(config);
+  SetDnsClient(std::move(dns_client));
+}
+
+bool FuzzedHostResolver::IsIPv6Reachable(const BoundNetLog& net_log) {
+  return is_ipv6_reachable_;
+}
+
+void FuzzedHostResolver::RunLoopbackProbeJob() {
+  SetHaveOnlyLoopbackAddresses(data_provider_->ConsumeBool());
+}
+
+}  // namespace net