// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40284755): Remove this and spanify to fix the errors.
#pragma allow_unsafe_buffers
#endif
#include "net/dns/dns_config_service_posix.h"
#include <memory>
#include <optional>
#include <string>
#include <type_traits>
#include <utility>
#include "base/files/file.h"
#include "base/files/file_path.h"
#include "base/files/file_path_watcher.h"
#include "base/functional/bind.h"
#include "base/lazy_instance.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/memory/raw_ptr.h"
#include "base/sequence_checker.h"
#include "base/task/single_thread_task_runner.h"
#include "base/threading/scoped_blocking_call.h"
#include "base/time/time.h"
#include "build/build_config.h"
#include "net/base/ip_endpoint.h"
#include "net/dns/dns_config.h"
#include "net/dns/dns_hosts.h"
#include "net/dns/notify_watcher_mac.h"
#include "net/dns/public/resolv_reader.h"
#include "net/dns/serial_worker.h"
#if BUILDFLAG(IS_MAC)
#include "net/dns/dns_config_watcher_mac.h"
#endif
namespace net {
namespace internal {
namespace {
const base::FilePath::CharType kFilePathHosts[] =
FILE_PATH_LITERAL("/etc/hosts");
#if BUILDFLAG(IS_IOS)
// There is no public API to watch the DNS configuration on iOS.
class DnsConfigWatcher {
public:
using CallbackType = base::RepeatingCallback<void(bool succeeded)>;
bool Watch(const CallbackType& callback) {
return false;
}
};
#elif BUILDFLAG(IS_MAC)
// DnsConfigWatcher for OS_MAC is in dns_config_watcher_mac.{hh,cc}.
#else // !BUILDFLAG(IS_IOS) && !BUILDFLAG(IS_MAC)
#ifndef _PATH_RESCONF // Normally defined in <resolv.h>
#define _PATH_RESCONF "/etc/resolv.conf"
#endif
const base::FilePath::CharType kFilePathConfig[] =
FILE_PATH_LITERAL(_PATH_RESCONF);
class DnsConfigWatcher {
public:
using CallbackType = base::RepeatingCallback<void(bool succeeded)>;
bool Watch(const CallbackType& callback) {
callback_ = callback;
return watcher_.Watch(base::FilePath(kFilePathConfig),
base::FilePathWatcher::Type::kNonRecursive,
base::BindRepeating(&DnsConfigWatcher::OnCallback,
base::Unretained(this)));
}
private:
void OnCallback(const base::FilePath& path, bool error) {
callback_.Run(!error);
}
base::FilePathWatcher watcher_;
CallbackType callback_;
};
#endif // BUILDFLAG(IS_IOS)
std::optional<DnsConfig> ReadDnsConfig() {
base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
base::BlockingType::MAY_BLOCK);
std::optional<DnsConfig> dns_config;
{
std::unique_ptr<ScopedResState> scoped_res_state =
ResolvReader().GetResState();
if (scoped_res_state) {
dns_config = ConvertResStateToDnsConfig(scoped_res_state->state());
}
}
if (!dns_config.has_value())
return dns_config;
#if BUILDFLAG(IS_MAC)
if (!DnsConfigWatcher::CheckDnsConfig(
dns_config->unhandled_options /* out_unhandled_options */)) {
return std::nullopt;
}
#endif // BUILDFLAG(IS_MAC)
// Override |fallback_period| value to match default setting on Windows.
dns_config->fallback_period = kDnsDefaultFallbackPeriod;
return dns_config;
}
} // namespace
class DnsConfigServicePosix::Watcher : public DnsConfigService::Watcher {
public:
explicit Watcher(DnsConfigServicePosix& service)
: DnsConfigService::Watcher(service) {}
Watcher(const Watcher&) = delete;
Watcher& operator=(const Watcher&) = delete;
~Watcher() override = default;
bool Watch() override {
CheckOnCorrectSequence();
bool success = true;
if (!config_watcher_.Watch(base::BindRepeating(&Watcher::OnConfigChanged,
base::Unretained(this)))) {
LOG(ERROR) << "DNS config watch failed to start.";
success = false;
}
// Hosts file should never change on iOS, so don't watch it there.
#if !BUILDFLAG(IS_IOS)
if (!hosts_watcher_.Watch(
base::FilePath(kFilePathHosts),
base::FilePathWatcher::Type::kNonRecursive,
base::BindRepeating(&Watcher::OnHostsFilePathWatcherChange,
base::Unretained(this)))) {
LOG(ERROR) << "DNS hosts watch failed to start.";
success = false;
}
#endif // !BUILDFLAG(IS_IOS)
return success;
}
private:
#if !BUILDFLAG(IS_IOS)
void OnHostsFilePathWatcherChange(const base::FilePath& path, bool error) {
OnHostsChanged(!error);
}
#endif // !BUILDFLAG(IS_IOS)
DnsConfigWatcher config_watcher_;
#if !BUILDFLAG(IS_IOS)
base::FilePathWatcher hosts_watcher_;
#endif // !BUILDFLAG(IS_IOS)
};
// A SerialWorker that uses libresolv to initialize res_state and converts
// it to DnsConfig.
class DnsConfigServicePosix::ConfigReader : public SerialWorker {
public:
explicit ConfigReader(DnsConfigServicePosix& service) : service_(&service) {
// Allow execution on another thread; nothing thread-specific about
// constructor.
DETACH_FROM_SEQUENCE(sequence_checker_);
}
~ConfigReader() override = default;
ConfigReader(const ConfigReader&) = delete;
ConfigReader& operator=(const ConfigReader&) = delete;
std::unique_ptr<SerialWorker::WorkItem> CreateWorkItem() override {
return std::make_unique<WorkItem>();
}
bool OnWorkFinished(std::unique_ptr<SerialWorker::WorkItem>
serial_worker_work_item) override {
DCHECK(serial_worker_work_item);
DCHECK(!IsCancelled());
WorkItem* work_item = static_cast<WorkItem*>(serial_worker_work_item.get());
if (work_item->dns_config_.has_value()) {
service_->OnConfigRead(std::move(work_item->dns_config_).value());
return true;
} else {
LOG(WARNING) << "Failed to read DnsConfig.";
return false;
}
}
private:
class WorkItem : public SerialWorker::WorkItem {
public:
void DoWork() override { dns_config_ = ReadDnsConfig(); }
private:
friend class ConfigReader;
std::optional<DnsConfig> dns_config_;
};
// Raw pointer to owning DnsConfigService.
const raw_ptr<DnsConfigServicePosix> service_;
};
DnsConfigServicePosix::DnsConfigServicePosix()
: DnsConfigService(kFilePathHosts) {
// Allow constructing on one thread and living on another.
DETACH_FROM_SEQUENCE(sequence_checker_);
}
DnsConfigServicePosix::~DnsConfigServicePosix() {
if (config_reader_)
config_reader_->Cancel();
}
void DnsConfigServicePosix::RefreshConfig() {
InvalidateConfig();
InvalidateHosts();
ReadConfigNow();
ReadHostsNow();
}
void DnsConfigServicePosix::ReadConfigNow() {
if (!config_reader_)
CreateReader();
config_reader_->WorkNow();
}
bool DnsConfigServicePosix::StartWatching() {
CreateReader();
// TODO(szym): re-start watcher if that makes sense. http://crbug.com/116139
watcher_ = std::make_unique<Watcher>(*this);
return watcher_->Watch();
}
void DnsConfigServicePosix::CreateReader() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
DCHECK(!config_reader_);
config_reader_ = std::make_unique<ConfigReader>(*this);
}
std::optional<DnsConfig> ConvertResStateToDnsConfig(
const struct __res_state& res) {
DnsConfig dns_config;
dns_config.unhandled_options = false;
if (!(res.options & RES_INIT))
return std::nullopt;
std::optional<std::vector<IPEndPoint>> nameservers = GetNameservers(res);
if (!nameservers)
return std::nullopt;
dns_config.nameservers = std::move(*nameservers);
dns_config.search.clear();
for (int i = 0; (i < MAXDNSRCH) && res.dnsrch[i]; ++i) {
dns_config.search.emplace_back(res.dnsrch[i]);
}
dns_config.ndots = res.ndots;
dns_config.fallback_period = base::Seconds(res.retrans);
dns_config.attempts = res.retry;
#if defined(RES_ROTATE)
dns_config.rotate = res.options & RES_ROTATE;
#endif
#if !defined(RES_USE_DNSSEC)
// Some versions of libresolv don't have support for the DO bit. In this
// case, we proceed without it.
static const int RES_USE_DNSSEC = 0;
#endif
// The current implementation assumes these options are set. They normally
// cannot be overwritten by /etc/resolv.conf
const unsigned kRequiredOptions = RES_RECURSE | RES_DEFNAMES | RES_DNSRCH;
if ((res.options & kRequiredOptions) != kRequiredOptions) {
dns_config.unhandled_options = true;
return dns_config;
}
const unsigned kUnhandledOptions = RES_USEVC | RES_IGNTC | RES_USE_DNSSEC;
if (res.options & kUnhandledOptions) {
dns_config.unhandled_options = true;
return dns_config;
}
if (dns_config.nameservers.empty())
return std::nullopt;
// If any name server is 0.0.0.0, assume the configuration is invalid.
// TODO(szym): Measure how often this happens. http://crbug.com/125599
for (const IPEndPoint& nameserver : dns_config.nameservers) {
if (nameserver.address().IsZero())
return std::nullopt;
}
return dns_config;
}
} // namespace internal
// static
std::unique_ptr<DnsConfigService> DnsConfigService::CreateSystemService() {
// DnsConfigService on iOS doesn't watch the config so its result can become
// inaccurate at any time. Disable it to prevent promulgation of inaccurate
// DnsConfigs.
#if BUILDFLAG(IS_IOS)
return nullptr;
#else // BUILDFLAG(IS_IOS)
return std::make_unique<internal::DnsConfigServicePosix>();
#endif // BUILDFLAG(IS_IOS)
}
} // namespace net
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