arc/network/arc_service.cc

// Copyright 2019 The Chromium OS 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 "arc/network/arc_service.h"

#include <linux/rtnetlink.h>
#include <net/if.h>

#include <utility>
#include <vector>

#include <base/bind.h>
#include <base/files/file_path.h>
#include <base/files/file_util.h>
#include <base/logging.h>
#include <base/strings/string_number_conversions.h>
#include <base/strings/string_util.h>
#include <base/strings/stringprintf.h>
#include <brillo/key_value_store.h>
#include <chromeos/constants/vm_tools.h>
#include <shill/net/rtnl_message.h>

#include "arc/network/datapath.h"
#include "arc/network/mac_address_generator.h"
#include "arc/network/manager.h"
#include "arc/network/minijailed_process_runner.h"
#include "arc/network/net_util.h"
#include "arc/network/scoped_ns.h"

namespace arc_networkd {

namespace test {
GuestMessage::GuestType guest = GuestMessage::UNKNOWN_GUEST;
}  // namespace test

namespace {
constexpr pid_t kInvalidPID = 0;
constexpr pid_t kTestPID = -2;
constexpr uint32_t kInvalidCID = 0;
constexpr int kInvalidTableID = -1;
constexpr int kMaxTableRetries = 10;  // Based on 1 second delay.
constexpr base::TimeDelta kTableRetryDelay = base::TimeDelta::FromSeconds(1);
// Android adds a constant to the interface index to derive the table id.
// This is defined in system/netd/server/RouteController.h
constexpr int kRouteControllerRouteTableOffsetFromIndex = 1000;
constexpr int kMultinetMinAndroidSdkVersion = 28;
constexpr char kMultinetFeatureName[] = "ARC multi-networking";

// This wrapper is required since the base class is a singleton that hides its
// constructor. It is necessary here because the message loop thread has to be
// reassociated to the container's network namespace; and since the container
// can be repeatedly created and destroyed, the handler must be as well.
class RTNetlinkHandler : public shill::RTNLHandler {
 public:
  RTNetlinkHandler() = default;
  ~RTNetlinkHandler() = default;

 private:
  DISALLOW_COPY_AND_ASSIGN(RTNetlinkHandler);
};

int GetAndroidRoutingTableId(const std::string& ifname, pid_t pid) {
  base::FilePath ifindex_path(base::StringPrintf(
      "/proc/%d/root/sys/class/net/%s/ifindex", pid, ifname.c_str()));
  std::string contents;
  if (!base::ReadFileToString(ifindex_path, &contents)) {
    PLOG(WARNING) << "Could not read " << ifindex_path.value();
    return kInvalidTableID;
  }

  base::TrimWhitespaceASCII(contents, base::TRIM_TRAILING, &contents);
  int table_id = kInvalidTableID;
  if (!base::StringToInt(contents, &table_id)) {
    LOG(ERROR) << "Could not parse ifindex from " << ifindex_path.value()
               << ": " << contents;
    return kInvalidTableID;
  }
  table_id += kRouteControllerRouteTableOffsetFromIndex;

  LOG(INFO) << "Found table id " << table_id << " for container interface "
            << ifname;
  return table_id;
}

void OneTimeSetup(const Datapath& datapath) {
  static bool done = false;
  if (done)
    return;

  auto& runner = datapath.runner();

  // Load networking modules needed by Android that are not compiled in the
  // kernel. Android does not allow auto-loading of kernel modules.
  // These must succeed.
  if (runner.modprobe_all({
          // The netfilter modules needed by netd for iptables commands.
          "ip6table_filter",
          "ip6t_ipv6header",
          "ip6t_REJECT",
          // The xfrm modules needed for Android's ipsec APIs.
          "xfrm4_mode_transport",
          "xfrm4_mode_tunnel",
          "xfrm6_mode_transport",
          "xfrm6_mode_tunnel",
          // The ipsec modules for AH and ESP encryption for ipv6.
          "ah6",
          "esp6",
      }) != 0) {
    LOG(ERROR) << "One or more required kernel modules failed to load."
               << " Some Android functionality may be broken.";
  }
  // Optional modules.
  if (runner.modprobe_all({
          // This module is not available in kernels < 3.18
          "nf_reject_ipv6",
          // These modules are needed for supporting Chrome traffic on Android
          // VPN which uses Android's NAT feature. Android NAT sets up
          // iptables
          // rules that use these conntrack modules for FTP/TFTP.
          "nf_nat_ftp",
          "nf_nat_tftp",
          // The tun module is needed by the Android 464xlat clatd process.
          "tun",
      }) != 0) {
    LOG(WARNING) << "One or more optional kernel modules failed to load.";
  }

  // This is only needed for CTS (b/27932574).
  if (runner.chown("655360", "655360", "/sys/class/xt_idletimer") != 0) {
    LOG(ERROR) << "Failed to change ownership of xt_idletimer.";
  }

  done = true;
}

bool IsArcVm() {
  const base::FilePath path("/run/chrome/is_arcvm");
  std::string contents;
  if (!base::ReadFileToString(path, &contents)) {
    PLOG(ERROR) << "Could not read " << path.value();
  }
  return contents == "1";
}

GuestMessage::GuestType ArcGuest() {
  if (test::guest != GuestMessage::UNKNOWN_GUEST)
    return test::guest;

  return IsArcVm() ? GuestMessage::ARC_VM
                   : Manager::ShouldEnableFeature(kMultinetMinAndroidSdkVersion,
                                                  0, std::vector<std::string>(),
                                                  kMultinetFeatureName)
                         ? GuestMessage::ARC
                         : GuestMessage::ARC_LEGACY;
}

constexpr const char kArcDevicePrefix[] = "arc";
bool IsArcDevice(const std::string& ifname) {
  return base::StartsWith(ifname, kArcDevicePrefix,
                          base::CompareCase::INSENSITIVE_ASCII);
}

}  // namespace

ArcService::ArcService(DeviceManagerBase* dev_mgr, Datapath* datapath)
    : dev_mgr_(dev_mgr), datapath_(datapath) {
  DCHECK(dev_mgr_);
  DCHECK(datapath_);

  dev_mgr_->RegisterDeviceAddedHandler(
      GuestMessage::ARC,
      base::Bind(&ArcService::OnDeviceAdded, base::Unretained(this)));
  dev_mgr_->RegisterDeviceRemovedHandler(
      GuestMessage::ARC,
      base::Bind(&ArcService::OnDeviceRemoved, base::Unretained(this)));
  dev_mgr_->RegisterDefaultInterfaceChangedHandler(
      GuestMessage::ARC, base::Bind(&ArcService::OnDefaultInterfaceChanged,
                                    base::Unretained(this)));
}

ArcService::~ArcService() {
  if (impl_) {
    // Stop the service.
    Stop(impl_->id());
    // Delete all the bridges and veth pairs.
    dev_mgr_->ProcessDevices(
        base::Bind(&ArcService::OnDeviceRemoved, weak_factory_.GetWeakPtr()));
  }
  dev_mgr_->UnregisterAllGuestHandlers(GuestMessage::ARC);
}

bool ArcService::Start(uint32_t id) {
  if (impl_) {
    uint32_t prev_id;
    if (impl_->IsStarted(&prev_id)) {
      LOG(WARNING) << "Already running - did something crash?"
                   << " Stopping and restarting...";
      Stop(prev_id);
    }
  }

  const auto guest = ArcGuest();
  if (guest == GuestMessage::ARC_VM)
    impl_ = std::make_unique<VmImpl>(dev_mgr_, datapath_);
  else
    impl_ = std::make_unique<ContainerImpl>(dev_mgr_, datapath_, guest);

  if (!impl_->Start(id)) {
    impl_.reset();
    return false;
  }

  // Start known host devices, any new ones will be setup in the process.
  dev_mgr_->ProcessDevices(
      base::Bind(&ArcService::StartDevice, weak_factory_.GetWeakPtr()));

  // If this is the first time the service is starting this will create the
  // Android bridge device; otherwise it does nothing (this is a workaround for
  // the bug in Shill that casues a Bus crash when it sees the ARC bridge a
  // second time). Do this after processing the existing devices so it doesn't
  // get started twice.
  std::string arc;
  switch (guest) {
    case GuestMessage::ARC:
      arc = kAndroidDevice;
      break;
    case GuestMessage::ARC_LEGACY:
      arc = kAndroidLegacyDevice;
      break;
    case GuestMessage::ARC_VM:
      arc = kAndroidVmDevice;
      break;
    default:
      LOG(DFATAL) << "Unexpected guest: " << guest;
      return false;
  }
  dev_mgr_->Add(arc);
  dev_mgr_->OnGuestStart(guest);
  return true;
}

void ArcService::Stop(uint32_t id) {
  if (!impl_)
    return;

  dev_mgr_->OnGuestStop(impl_->guest());

  // Stop known host devices. Note that this does not teardown any existing
  // devices.
  dev_mgr_->ProcessDevices(
      base::Bind(&ArcService::StopDevice, weak_factory_.GetWeakPtr()));

  impl_->Stop(id);
  impl_.reset();
}

bool ArcService::AllowDevice(Device* device) const {
  if (!device->IsArc())
    return false;

  // ARC P+ is multi-network enabled and should process all devices.
  if ((impl_ && impl_->guest() == GuestMessage::ARC) ||
      (!impl_ && ArcGuest() == GuestMessage::ARC))
    return true;

  // ARC N and ARCVM (for now) are both single-network - meaning they only use
  // the "default" device which uses the default interface from shill.
  return device->UsesDefaultInterface();
}

void ArcService::OnDeviceAdded(Device* device) {
  if (!AllowDevice(device))
    return;

  const auto& config = device->config();

  LOG(INFO) << "Adding device " << device->ifname()
            << " bridge: " << config.host_ifname()
            << " guest_iface: " << config.guest_ifname();

  // Create the bridge.
  if (!datapath_->AddBridge(config.host_ifname(), config.host_ipv4_addr(),
                            30)) {
    // Per crbug/1008686 this device cannot be deleted and then re-added.
    // It could be that arc-networkd was restarted after a crash and this device
    // is being re-added.
    if (!device->IsAndroid()) {
      LOG(ERROR) << "Failed to setup arc bridge: " << config.host_ifname();
      return;
    }
    if (!datapath_->MaskInterfaceFlags(config.host_ifname(), IFF_UP)) {
      LOG(ERROR) << "Failed to bring up arc bridge: " << config.host_ifname();
      return;
    }
  }

  // Setup the iptables.
  if (device->UsesDefaultInterface()) {
    if (!datapath_->AddLegacyIPv4DNAT(
            IPv4AddressToString(config.guest_ipv4_addr())))
      LOG(ERROR) << "Failed to configure ARC traffic rules";

    if (!datapath_->AddOutboundIPv4(config.host_ifname()))
      LOG(ERROR) << "Failed to configure egress traffic rules";
  } else if (!device->IsAndroid()) {
    if (!datapath_->AddInboundIPv4DNAT(
            device->ifname(), IPv4AddressToString(config.guest_ipv4_addr())))
      LOG(ERROR) << "Failed to configure ingress traffic rules for "
                 << device->ifname();

    if (!datapath_->AddOutboundIPv4(config.host_ifname()))
      LOG(ERROR) << "Failed to configure egress traffic rules";
  }

  device->set_context(std::make_unique<Context>());

  StartDevice(device);
}

void ArcService::StartDevice(Device* device) {
  if (!AllowDevice(device))
    return;

  // This can happen if OnDeviceAdded is invoked when the container is down.
  if (!impl_ || !impl_->IsStarted())
    return;

  // If there is no context, then this is a new device and it needs to run
  // through the full setup process.
  Context* ctx = dynamic_cast<Context*>(device->context());
  if (!ctx)
    return OnDeviceAdded(device);

  if (ctx->IsStarted()) {
    LOG(ERROR) << "Attempt to restart device " << device->ifname();
    return;
  }

  if (!impl_->OnStartDevice(device)) {
    LOG(ERROR) << "Failed to start device " << device->ifname();
    return;
  }

  ctx->Start();
}

void ArcService::OnDeviceRemoved(Device* device) {
  if (!AllowDevice(device))
    return;

  // If the container is down, this call does nothing.
  StopDevice(device);

  const auto& config = device->config();

  LOG(INFO) << "Removing device " << device->ifname()
            << " bridge: " << config.host_ifname()
            << " guest_iface: " << config.guest_ifname();

  device->StopIPv6RoutingLegacy();
  if (device->UsesDefaultInterface()) {
    datapath_->RemoveOutboundIPv4(config.host_ifname());
    datapath_->RemoveLegacyIPv4DNAT();
  } else if (!device->IsAndroid()) {
    datapath_->RemoveOutboundIPv4(config.host_ifname());
    datapath_->RemoveInboundIPv4DNAT(
        device->ifname(), IPv4AddressToString(config.guest_ipv4_addr()));
  }

  // Per crbug/1008686 this device cannot be deleted and then re-added.
  // So instead of removing the bridge, bring it down and mark it. This will
  // allow us to detect if the device is re-added in case of a crash restart and
  // do the right thing.
  if (device->IsAndroid()) {
    // This can be safely deleted now.
    datapath_->RemoveInterface(ArcVethHostName("arc0"));
    if (!datapath_->MaskInterfaceFlags(config.host_ifname(), IFF_DEBUG, IFF_UP))
      LOG(ERROR) << "Failed to bring down arc bridge "
                 << "- it may not restart correctly";
  } else {
    datapath_->RemoveBridge(config.host_ifname());
  }

  device->set_context(nullptr);
}

void ArcService::StopDevice(Device* device) {
  if (!AllowDevice(device))
    return;

  // This can happen if the device if OnDeviceRemoved is invoked when the
  // container is down.
  if (!impl_ || !impl_->IsStarted())
    return;

  Context* ctx = dynamic_cast<Context*>(device->context());
  if (!ctx) {
    LOG(ERROR) << "Attempt to stop removed device " << device->ifname();
    return;
  }

  if (!ctx->IsStarted()) {
    LOG(ERROR) << "Attempt to re-stop device " << device->ifname();
    return;
  }

  impl_->OnStopDevice(device);

  ctx->Stop();
}

void ArcService::OnDefaultInterfaceChanged(const std::string& ifname) {
  if (impl_)
    impl_->OnDefaultInterfaceChanged(ifname);
}

// Context

ArcService::Context::Context() : Device::Context() {
  Stop();
}

void ArcService::Context::Start() {
  Stop();
  started_ = true;
}

void ArcService::Context::Stop() {
  started_ = false;
  link_up_ = false;
  routing_table_id_ = kInvalidTableID;
  routing_table_attempts_ = 0;
}

bool ArcService::Context::IsStarted() const {
  return started_;
}

bool ArcService::Context::IsLinkUp() const {
  return link_up_;
}

bool ArcService::Context::SetLinkUp(bool link_up) {
  if (link_up == link_up_)
    return false;

  link_up_ = link_up;
  return true;
}

bool ArcService::Context::HasIPv6() const {
  return routing_table_id_ != kInvalidTableID;
}

bool ArcService::Context::SetHasIPv6(int routing_table_id) {
  if (routing_table_id <= kRouteControllerRouteTableOffsetFromIndex)
    return false;

  routing_table_id_ = routing_table_id;
  return true;
}

void ArcService::Context::ClearIPv6() {
  routing_table_id_ = kInvalidTableID;
  routing_table_attempts_ = 0;
}

int ArcService::Context::RoutingTableID() const {
  return routing_table_id_;
}

int ArcService::Context::RoutingTableAttempts() {
  return routing_table_attempts_++;
}

const std::string& ArcService::Context::TAP() const {
  return tap_;
}

void ArcService::Context::SetTAP(const std::string& tap) {
  tap_ = tap;
}

// ARC++ specific functions.

ArcService::ContainerImpl::ContainerImpl(DeviceManagerBase* dev_mgr,
                                         Datapath* datapath,
                                         GuestMessage::GuestType guest)
    : pid_(kInvalidPID), dev_mgr_(dev_mgr), datapath_(datapath), guest_(guest) {
  OneTimeSetup(*datapath_);
}

GuestMessage::GuestType ArcService::ContainerImpl::guest() const {
  return guest_;
}

uint32_t ArcService::ContainerImpl::id() const {
  return pid_;
}

bool ArcService::ContainerImpl::Start(uint32_t pid) {
  // This could happen if something crashes and the stop signal is not sent.
  // It can probably be addressed by stopping and restarting the service.
  if (pid_ != kInvalidPID)
    return false;

  // TODO(garrick): Remove this test hack.
  if (pid == kTestPID) {
    LOG(WARNING) << "Running with test PID";
    pid_ = pid;
    return true;
  }
  if (pid == kInvalidPID) {
    LOG(ERROR) << "Cannot start service - invalid container PID";
    return false;
  }
  pid_ = pid;

  // Start listening for RTNetlink messages to be notified when a virtual ARC
  // interface is brought up or down.
  // TODO(garrick): Delete when NDProxy is enabled on all boards.
  {
    host_link_listener_ = std::make_unique<shill::RTNLListener>(
        shill::RTNLHandler::kRequestLink,
        Bind(&ArcService::ContainerImpl::HostLinkMsgHandler,
             weak_factory_.GetWeakPtr()));
    shill::RTNLHandler::GetInstance()->Start(RTMGRP_LINK);
  }

  // Start listening for RTNetlink messages in the container's net namespace
  // to be notified whenever it brings up an interface.
  {
    ScopedNS ns(pid_);
    if (ns.IsValid()) {
      rtnl_handler_ = std::make_unique<RTNetlinkHandler>();
      rtnl_handler_->Start(RTMGRP_LINK);
      link_listener_ = std::make_unique<shill::RTNLListener>(
          shill::RTNLHandler::kRequestLink,
          Bind(&ArcService::ContainerImpl::LinkMsgHandler,
               weak_factory_.GetWeakPtr()),
          rtnl_handler_.get());
    } else {
      // This is bad - it means we won't ever be able to tell when the container
      // brings up an interface.
      LOG(ERROR)
          << "Cannot start netlink listener - invalid container namespace?";
      return false;
    }
  }

  LOG(INFO) << "ARC++ network service started {pid: " << pid_ << "}";
  return true;
}

void ArcService::ContainerImpl::Stop(uint32_t /*pid*/) {
  if (!IsStarted())
    return;

  rtnl_handler_->RemoveListener(link_listener_.get());
  link_listener_.reset();
  rtnl_handler_.reset();

  LOG(INFO) << "ARC++ network service stopped {pid: " << pid_ << "}";
  pid_ = kInvalidPID;
}

bool ArcService::ContainerImpl::IsStarted(uint32_t* pid) const {
  if (pid)
    *pid = pid_;

  return pid_ != kInvalidPID;
}

bool ArcService::ContainerImpl::OnStartDevice(Device* device) {
  const auto& config = device->config();

  LOG(INFO) << "Starting device " << device->ifname()
            << " bridge: " << config.host_ifname()
            << " guest_iface: " << config.guest_ifname() << " pid: " << pid_;

  std::string veth_ifname = datapath_->AddVirtualBridgedInterface(
      device->ifname(), MacAddressToString(config.guest_mac_addr()),
      config.host_ifname());
  if (veth_ifname.empty()) {
    LOG(ERROR) << "Failed to create virtual interface for container";
    return false;
  }

  if (!datapath_->AddInterfaceToContainer(
          pid_, veth_ifname, config.guest_ifname(), config.guest_ipv4_addr(),
          30, device->options().fwd_multicast)) {
    LOG(ERROR) << "Failed to create container interface.";
    datapath_->RemoveInterface(veth_ifname);
    return false;
  }

  // Setup callback for legacy IPv6 discovery, if applicable.
  if (device->options().ipv6_enabled &&
      device->options().find_ipv6_routes_legacy) {
    device->RegisterIPv6Handlers(
        base::Bind(&ArcService::ContainerImpl::SetupIPv6,
                   weak_factory_.GetWeakPtr()),
        base::Bind(&ArcService::ContainerImpl::TeardownIPv6,
                   weak_factory_.GetWeakPtr()));
  }

  // Signal the container that the network device is ready.
  if (device->IsAndroid()) {
    datapath_->runner().WriteSentinelToContainer(base::IntToString(pid_));
  }

  dev_mgr_->StartForwarding(*device);
  return true;
}

void ArcService::ContainerImpl::OnStopDevice(Device* device) {
  const auto& config = device->config();

  LOG(INFO) << "Stopping device " << device->ifname()
            << " bridge: " << config.host_ifname()
            << " guest_iface: " << config.guest_ifname() << " pid: " << pid_;

  device->StopIPv6RoutingLegacy();
  if (!device->IsAndroid()) {
    datapath_->RemoveInterface(ArcVethHostName(device->ifname()));
  }

  device->UnregisterIPv6Handlers();
}

void ArcService::ContainerImpl::OnDefaultInterfaceChanged(
    const std::string& ifname) {
  if (!IsStarted())
    return;

  // For ARC N, we must always be able to find the arc0 device and, at a
  // minimum, disable it.
  if (guest() == GuestMessage::ARC_LEGACY) {
    datapath_->RemoveLegacyIPv4InboundDNAT();
    auto* device = dev_mgr_->FindByGuestInterface("arc0");
    if (!device) {
      LOG(DFATAL) << "Expected legacy Android device missing";
      return;
    }
    device->StopIPv6RoutingLegacy();

    // If a new default interface was given, then re-enable with that.
    if (!ifname.empty()) {
      datapath_->AddLegacyIPv4InboundDNAT(ifname);
      device->StartIPv6RoutingLegacy(ifname);
    }
    return;
  }

  // For ARC P and later, we're only concerned with resetting the device when it
  // becomes the default (again) in order to ensure any previous configuration.
  // is cleared.
  if (ifname.empty())
    return;

  auto* device = dev_mgr_->FindByGuestInterface(ifname);
  if (!device) {
    LOG(ERROR) << "Expected default device missing: " << ifname;
    return;
  }
  device->StopIPv6RoutingLegacy();
  device->StartIPv6RoutingLegacy(ifname);
}

void ArcService::ContainerImpl::LinkMsgHandler(const shill::RTNLMessage& msg) {
  if (!msg.HasAttribute(IFLA_IFNAME)) {
    LOG(ERROR) << "Link event message does not have IFLA_IFNAME";
    return;
  }
  bool link_up = msg.link_status().flags & IFF_UP;
  shill::ByteString b(msg.GetAttribute(IFLA_IFNAME));
  std::string ifname(reinterpret_cast<const char*>(
      b.GetSubstring(0, IFNAMSIZ).GetConstData()));

  auto* device = dev_mgr_->FindByGuestInterface(ifname);
  if (!device)
    return;

  Context* ctx = dynamic_cast<Context*>(device->context());
  if (!ctx) {
    LOG(DFATAL) << "Context missing";
    return;
  }

  // If the link status is unchanged, there is nothing to do.
  if (!ctx->SetLinkUp(link_up))
    return;

  if (!link_up) {
    LOG(INFO) << ifname << " is now down";
    return;
  }
  LOG(INFO) << ifname << " is now up";

  if (device->UsesDefaultInterface()) {
    OnDefaultInterfaceChanged(dev_mgr_->DefaultInterface());
    return;
  }

  if (device->IsAndroid())
    return;

  device->StartIPv6RoutingLegacy(ifname);
}

// TODO(garrick): Remove once NDProxy is enabled on all boards.
void ArcService::ContainerImpl::HostLinkMsgHandler(
    const shill::RTNLMessage& msg) {
  if (!msg.HasAttribute(IFLA_IFNAME)) {
    LOG(ERROR) << "Link event message does not have IFLA_IFNAME";
    return;
  }

  // Only consider virtual interfaces that were created for guests; for now this
  // only includes those prefixed with 'arc'.
  shill::ByteString b(msg.GetAttribute(IFLA_IFNAME));
  std::string ifname(reinterpret_cast<const char*>(
      b.GetSubstring(0, IFNAMSIZ).GetConstData()));
  if (!IsArcDevice(ifname))
    return;

  bool link_up = msg.link_status().flags & IFF_UP;
  Device* device = dev_mgr_->FindByHostInterface(ifname);

  if (!device || !device->HostLinkUp(link_up))
    return;

  if (!link_up) {
    LOG(INFO) << ifname << " is now down";
    device->StopIPv6RoutingLegacy();
    return;
  }

  // The link is now up.
  LOG(INFO) << ifname << " is now up";

  if (device->UsesDefaultInterface())
    device->StartIPv6RoutingLegacy(dev_mgr_->DefaultInterface());
  else if (!device->IsAndroid())
    device->StartIPv6RoutingLegacy(device->config().guest_ifname());
}

void ArcService::ContainerImpl::SetupIPv6(Device* device) {
  auto& ipv6_config = device->ipv6_config();
  if (ipv6_config.ifname.empty())
    return;

  Context* ctx = dynamic_cast<Context*>(device->context());
  if (!ctx) {
    LOG(DFATAL) << "Context missing";
    return;
  }
  if (ctx->HasIPv6())
    return;

  LOG(INFO) << "Setting up IPv6 for " << ipv6_config.ifname;

  int table_id =
      GetAndroidRoutingTableId(device->config().guest_ifname(), pid_);
  if (table_id == kInvalidTableID) {
    if (ctx->RoutingTableAttempts() < kMaxTableRetries) {
      LOG(INFO) << "Could not look up routing table ID for container interface "
                << device->config().guest_ifname() << " - trying again...";
      base::MessageLoop::current()->task_runner()->PostDelayedTask(
          FROM_HERE,
          base::Bind(&ArcService::ContainerImpl::SetupIPv6,
                     weak_factory_.GetWeakPtr(), device),
          kTableRetryDelay);
    } else {
      LOG(DFATAL)
          << "Could not look up routing table ID for container interface "
          << device->config().guest_ifname();
    }
    return;
  }

  LOG(INFO) << "Setting IPv6 address " << ipv6_config.addr
            << "/128, gateway=" << ipv6_config.router << " on "
            << ipv6_config.ifname;

  char buf[INET6_ADDRSTRLEN] = {0};
  if (!inet_ntop(AF_INET6, &ipv6_config.addr, buf, sizeof(buf))) {
    LOG(DFATAL) << "Invalid address: " << ipv6_config.addr;
    return;
  }
  std::string addr = buf;

  if (!inet_ntop(AF_INET6, &ipv6_config.router, buf, sizeof(buf))) {
    LOG(DFATAL) << "Invalid router address: " << ipv6_config.router;
    return;
  }
  std::string router = buf;

  const auto& config = device->config();
  {
    ScopedNS ns(pid_);
    if (!ns.IsValid()) {
      LOG(ERROR) << "Invalid container namespace (" << pid_
                 << ") - cannot configure IPv6.";
      return;
    }
    // Tag the interface so that ARC can detect this manual configuration and
    // skip disabling and re-enabling IPv6 (b/144545910).
    if (!datapath_->MaskInterfaceFlags(config.guest_ifname(), IFF_DEBUG)) {
      LOG(ERROR) << "Failed to mark IPv6 manual config flag on interface";
    }
    if (!datapath_->AddIPv6GatewayRoutes(config.guest_ifname(), addr, router,
                                         ipv6_config.prefix_len, table_id)) {
      LOG(ERROR) << "Failed to setup IPv6 routes in the container";
      return;
    }
  }

  if (!datapath_->AddIPv6HostRoute(config.host_ifname(), addr, 128)) {
    LOG(ERROR) << "Failed to setup the IPv6 route for interface "
               << config.host_ifname();
    return;
  }

  if (!datapath_->AddIPv6Neighbor(ipv6_config.ifname, addr)) {
    LOG(ERROR) << "Failed to setup the IPv6 neighbor proxy";
    datapath_->RemoveIPv6HostRoute(config.host_ifname(), addr, 128);
    return;
  }

  if (!datapath_->AddIPv6Forwarding(ipv6_config.ifname,
                                    device->config().host_ifname())) {
    LOG(ERROR) << "Failed to setup iptables for IPv6";
    datapath_->RemoveIPv6Neighbor(ipv6_config.ifname, addr);
    datapath_->RemoveIPv6HostRoute(config.host_ifname(), addr, 128);
    return;
  }

  ctx->SetHasIPv6(table_id);
}

void ArcService::ContainerImpl::TeardownIPv6(Device* device) {
  Context* ctx = dynamic_cast<Context*>(device->context());
  if (!ctx || !ctx->HasIPv6())
    return;

  auto& ipv6_config = device->ipv6_config();
  LOG(INFO) << "Clearing IPv6 for " << ipv6_config.ifname;
  int table_id = ctx->RoutingTableID();
  ctx->ClearIPv6();

  char buf[INET6_ADDRSTRLEN] = {0};
  if (!inet_ntop(AF_INET6, &ipv6_config.addr, buf, sizeof(buf))) {
    LOG(DFATAL) << "Invalid address: " << ipv6_config.addr;
    return;
  }
  std::string addr = buf;

  if (!inet_ntop(AF_INET6, &ipv6_config.router, buf, sizeof(buf))) {
    LOG(DFATAL) << "Invalid router address: " << ipv6_config.router;
    return;
  }
  std::string router = buf;

  const auto& config = device->config();
  datapath_->RemoveIPv6Forwarding(ipv6_config.ifname, config.host_ifname());
  datapath_->RemoveIPv6Neighbor(ipv6_config.ifname, addr);
  datapath_->RemoveIPv6HostRoute(config.host_ifname(), addr, 128);

  ScopedNS ns(pid_);
  if (ns.IsValid()) {
    datapath_->RemoveIPv6GatewayRoutes(config.guest_ifname(), addr, router,
                                       ipv6_config.prefix_len, table_id);
  }
}

// VM specific functions

ArcService::VmImpl::VmImpl(DeviceManagerBase* dev_mgr, Datapath* datapath)
    : cid_(kInvalidCID), dev_mgr_(dev_mgr), datapath_(datapath) {}

GuestMessage::GuestType ArcService::VmImpl::guest() const {
  return GuestMessage::ARC_VM;
}

uint32_t ArcService::VmImpl::id() const {
  return cid_;
}

bool ArcService::VmImpl::Start(uint32_t cid) {
  // This can happen if concierge crashes and doesn't send the vm down RPC.
  // It can probably be addressed by stopping and restarting the service.
  if (cid_ != kInvalidCID)
    return false;

  if (cid == kInvalidCID) {
    LOG(ERROR) << "Invalid VM cid " << cid;
    return false;
  }

  cid_ = cid;
  LOG(INFO) << "ARCVM network service started {cid: " << cid_ << "}";

  return true;
}

void ArcService::VmImpl::Stop(uint32_t cid) {
  if (cid_ != cid) {
    LOG(ERROR) << "Mismatched ARCVM CIDs " << cid_ << " != " << cid;
    return;
  }

  LOG(INFO) << "ARCVM network service stopped {cid: " << cid_ << "}";
  cid_ = kInvalidCID;
}

bool ArcService::VmImpl::IsStarted(uint32_t* cid) const {
  if (cid)
    *cid = cid_;

  return cid_ != kInvalidCID;
}

bool ArcService::VmImpl::OnStartDevice(Device* device) {
  // TODO(garrick): Remove this once ARCVM supports ad hoc interface
  // configurations.
  if (!device->UsesDefaultInterface())
    return false;

  const auto& config = device->config();

  LOG(INFO) << "Starting device " << device->ifname()
            << " bridge: " << config.host_ifname()
            << " guest_iface: " << config.guest_ifname() << " cid: " << cid_;

  Context* ctx = dynamic_cast<Context*>(device->context());
  if (!ctx) {
    LOG(ERROR) << "Context missing";
    return false;
  }

  // Since the interface will be added to the bridge, no address configuration
  // should be provided here.
  std::string tap =
      datapath_->AddTAP("" /* auto-generate name */, nullptr /* no mac addr */,
                        nullptr /* no ipv4 subnet */, vm_tools::kCrosVmUser);
  if (tap.empty()) {
    LOG(ERROR) << "Failed to create TAP device for VM";
    return false;
  }

  if (!datapath_->AddToBridge(config.host_ifname(), tap)) {
    LOG(ERROR) << "Failed to bridge TAP device " << tap;
    datapath_->RemoveInterface(tap);
    return false;
  }

  ctx->SetTAP(tap);
  // TODO(garrick): Remove this once ARCVM supports ad hoc interface
  // configurations; but for now ARCVM needs to be treated like ARC++ N.
  OnDefaultInterfaceChanged(dev_mgr_->DefaultInterface());
  dev_mgr_->StartForwarding(*device);
  return true;
}

void ArcService::VmImpl::OnStopDevice(Device* device) {
  // TODO(garrick): Remove this once ARCVM supports ad hoc interface
  // configurations.
  if (!device->UsesDefaultInterface())
    return;

  const auto& config = device->config();

  LOG(INFO) << "Stopping " << device->ifname()
            << " bridge: " << config.host_ifname()
            << " guest_iface: " << config.guest_ifname() << " cid: " << cid_;

  Context* ctx = dynamic_cast<Context*>(device->context());
  if (!ctx) {
    LOG(ERROR) << "Context missing";
    return;
  }

  device->StopIPv6RoutingLegacy();
  datapath_->RemoveInterface(ctx->TAP());
}

void ArcService::VmImpl::OnDefaultInterfaceChanged(const std::string& ifname) {
  if (!IsStarted())
    return;

  // TODO(garrick): Remove this once ARCVM supports ad hoc interface
  // configurations; but for now ARCVM needs to be treated like ARC++ N.
  datapath_->RemoveLegacyIPv4InboundDNAT();
  auto* device = dev_mgr_->FindByGuestInterface("arc1");
  if (!device) {
    LOG(DFATAL) << "Expected Android device missing";
    return;
  }
  device->StopIPv6RoutingLegacy();

  // If a new default interface was given, then re-enable with that.
  if (!ifname.empty()) {
    datapath_->AddLegacyIPv4InboundDNAT(ifname);
    device->StartIPv6RoutingLegacy(ifname);
  }
}

}  // namespace arc_networkd