quiche/quic/qbone/bonnet/tun_device_packet_exchanger.cc

// Copyright (c) 2019 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 "quiche/quic/qbone/bonnet/tun_device_packet_exchanger.h"

#include <netinet/icmp6.h>
#include <netinet/ip6.h>
#include <sys/uio.h>

#include <algorithm>
#include <cerrno>
#include <cstddef>
#include <memory>
#include <string>

#include "absl/base/nullability.h"
#include "absl/status/status.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/string_view.h"
#include "absl/time/clock.h"
#include "absl/time/time.h"
#include "quiche/quic/core/quic_packets.h"
#include "quiche/quic/platform/api/quic_logging.h"
#include "quiche/quic/qbone/platform/icmp_packet.h"
#include "quiche/quic/qbone/platform/kernel_interface.h"
#include "quiche/quic/qbone/platform/netlink_interface.h"
#include "quiche/quic/qbone/qbone_client_interface.h"
#include "quiche/quic/qbone/qbone_constants.h"

namespace quic {

TunDevicePacketExchanger::TunDevicePacketExchanger(
    size_t mtu, KernelInterface* kernel, NetlinkInterface* netlink,
    Visitor* absl_nullable visitor, bool is_tap, StatsInterface* stats,
    absl::string_view ifname)
    : mtu_(mtu),
      kernel_(kernel),
      netlink_(netlink),
      visitor_(visitor),
      ifname_(ifname),
      is_tap_(is_tap),
      stats_(stats) {}

bool TunDevicePacketExchanger::ReadAndDeliverPacket(
    QboneClientInterface* qbone_client) {
  if (read_fd_ < 0) {
    std::string error =
        absl::StrCat("Invalid file descriptor of the TUN device: ", read_fd_);
    if (visitor_) {
      visitor_->OnReadError(error);
    }
    stats_->OnReadError(error);
    return false;
  }

  // Reading on a TUN device returns a packet at a time. If the packet is longer
  // than the buffer, it's truncated.
  auto read_buffer = std::make_unique<char[]>(mtu_);

  int result = 0;
  ethhdr eth_header;
  struct iovec iov[2];

  iov[0].iov_base = is_tap_ ? &eth_header : nullptr;
  iov[0].iov_len = is_tap_ ? ETH_HLEN : 0;
  iov[1].iov_base = read_buffer.get();
  iov[1].iov_len = mtu_;
  absl::Time start = absl::Now();
  result = kernel_->readv(read_fd_, iov, 2);

  absl::Duration latency = std::max(absl::Now() - start, absl::ZeroDuration());

  // Note that 0 means end of file, but we're talking about a TUN device - there
  // is no end of file. Therefore 0 also indicates error.
  if (result <= 0) {
    std::string error;
    if (errno == EAGAIN || errno == EWOULDBLOCK) {
      error =
          absl::ErrnoToStatus(errno, "Read from the TUN device was blocked.")
              .message();
      stats_->OnReadError(error);
    }
    // TODO(b/535980431): This passes an empty-string error for error codes
    // other than EAGAIN/EWOULDBLOCK, matching the behavior of a previous
    // implementation. Consider changing this to at least have a generic error
    // for any other cases.
    if (visitor_) {
      visitor_->OnReadError(error);
    }
    return false;
  }

  if (is_tap_ && result < ETH_HLEN) {
    std::string error = "Read packet too short for ethernet header.";
    if (visitor_) {
      visitor_->OnReadError(error);
    }
    stats_->OnReadError(error);
    return false;
  }

  size_t l3_packet_size = is_tap_ ? result - ETH_HLEN : result;
  auto buffer =
      std::make_unique<QuicData>(read_buffer.release(), l3_packet_size, true);
  if (is_tap_) {
    switch (ValidateL2Headers(eth_header, *buffer)) {
      case L2ValidationResult::kInvalid: {
        std::string error = "Invalid L2 headers.";
        if (visitor_) {
          visitor_->OnReadError(error);
        }
        stats_->OnReadError(error);
        return false;
      }
      case L2ValidationResult::kValidLinkLocal:
        // TODO(b/535980431): This returns false to match the behavior of a
        // previous implementation because no packet is forwarded to the tunnel,
        // but consider changing this to true. A link-local packet does not mean
        // there are no more packets to read from the TUN device.
        return false;
      case L2ValidationResult::kValidNormal:
        // Packet is valid and should be forwarded to the tunnel. Fall through
        // to normal processing.
        break;
    }
  }

  stats_->OnPacketRead(buffer->length(), latency);
  qbone_client->ProcessPacketFromNetwork(buffer->AsStringPiece());
  return true;
}

void TunDevicePacketExchanger::WritePacketToNetwork(const char* packet,
                                                    size_t size) {
  if (visitor_) {
    absl::Status status = visitor_->OnWrite(absl::string_view(packet, size));
    if (!status.ok()) {
      QUIC_LOG_EVERY_N_SEC(ERROR, 60) << status;
    }
  }

  if (write_fd_ < 0) {
    std::string error =
        absl::StrCat("Invalid file descriptor of the TUN device: ", write_fd_);
    QUIC_LOG_EVERY_N_SEC(ERROR, 60) << "Packet write failed: " << error;
    if (visitor_) {
      visitor_->OnWriteError(error);
    }
    stats_->OnWriteError(error);
    return;
  }

  if (is_tap_ && !eth_hdr_initialized_) {
    InitializeEthHdr();
  }
  struct iovec iov[2];
  iov[0].iov_base = is_tap_ ? &eth_hdr_ : nullptr;
  iov[0].iov_len = is_tap_ ? ETH_HLEN : 0;
  iov[1].iov_base = const_cast<char*>(packet);
  iov[1].iov_len = size;

  absl::Time start = absl::Now();
  int result = kernel_->writev(write_fd_, iov, 2);
  absl::Duration latency = std::max(absl::Now() - start, absl::ZeroDuration());

  if (result == -1) {
    std::string error;
    if (errno == EWOULDBLOCK || errno == EAGAIN) {
      // The tunnel is blocked. Note that this does not mean the receive
      // buffer of a TCP connection is filled. This simply means the TUN
      // device itself is blocked on handing packets to the rest of the
      // kernel.
      error = absl::ErrnoToStatus(errno, "Write to the TUN device was blocked.")
                  .message();
      stats_->OnWriteError(error);
    }

    // TODO(b/535980431): This logs/returns an empty-string error for error
    // codes other than EAGAIN/EWOULDBLOCK, matching the behavior of a previous
    // implementation. Consider changing this to at least have a generic error
    // for any other cases.
    QUIC_LOG_EVERY_N_SEC(ERROR, 60) << "Packet write failed: " << error;
    if (visitor_) {
      visitor_->OnWriteError(error);
    }
    return;
  }

  stats_->OnPacketWritten(result, latency);
}

void TunDevicePacketExchanger::set_read_file_descriptor(int fd) {
  read_fd_ = fd;
}
void TunDevicePacketExchanger::set_write_file_descriptor(int fd) {
  write_fd_ = fd;
}

const TunDevicePacketExchanger::StatsInterface*
TunDevicePacketExchanger::stats_interface() const {
  return stats_;
}

void TunDevicePacketExchanger::InitializeEthHdr() {
  if (!eth_hdr_initialized_) {
    NetlinkInterface::LinkInfo link_info{};
    if (netlink_->GetLinkInfo(ifname_, &link_info)) {
      // Set src & dst to my own address
      memcpy(&eth_hdr_.h_dest, link_info.hardware_address, ETH_ALEN);
      memcpy(&eth_hdr_.h_source, link_info.hardware_address, ETH_ALEN);
      // Assume ipv6 for now
      // TODO(b/195113643): Support additional protocols.
      eth_hdr_.h_proto = absl::ghtons(ETH_P_IPV6);
      eth_hdr_initialized_ = true;
    } else {
      QUIC_LOG_EVERY_N_SEC(ERROR, 30)
          << "Unable to get link info for: " << ifname_;
    }
  }
}

TunDevicePacketExchanger::L2ValidationResult
TunDevicePacketExchanger::ValidateL2Headers(const ethhdr& eth_header,
                                            const QuicData& packet) {
  if (eth_header.h_proto != absl::ghtons(ETH_P_IPV6)) {
    return L2ValidationResult::kInvalid;
  }
  constexpr auto kIp6PrefixLen = sizeof(ip6_hdr);
  constexpr auto kIcmp6PrefixLen = kIp6PrefixLen + sizeof(icmp6_hdr);
  if (packet.length() < kIp6PrefixLen) {
    // Packet is too short to be ipv6. Drop it.
    return L2ValidationResult::kInvalid;
  }
  auto* ip_hdr = reinterpret_cast<const ip6_hdr*>(packet.data());
  const bool is_icmp = ip_hdr->ip6_ctlun.ip6_un1.ip6_un1_nxt == IPPROTO_ICMPV6;

  bool is_neighbor_solicit = false;
  if (is_icmp) {
    if (packet.length() < kIcmp6PrefixLen) {
      // Packet is too short to be icmp6. Drop it.
      return L2ValidationResult::kInvalid;
    }
    is_neighbor_solicit =
        reinterpret_cast<const icmp6_hdr*>(packet.data() + kIp6PrefixLen)
            ->icmp6_type == ND_NEIGHBOR_SOLICIT;
  }

  if (is_neighbor_solicit) {
    // We need the local interface MAC address to respond.
    if (!eth_hdr_initialized_) {
      InitializeEthHdr();
    }
    // If we've received a neighbor solicitation, craft an advertisement to
    // respond with and write it back to the local interface.
    auto* icmp6_payload = packet.data() + kIcmp6PrefixLen;

    QuicIpAddress target_address(
        *reinterpret_cast<const in6_addr*>(icmp6_payload));
    if (target_address != *QboneConstants::GatewayAddress()) {
      // Only respond to solicitations for our gateway address
      return L2ValidationResult::kValidLinkLocal;
    }

    // Neighbor Advertisement crafted per:
    // https://datatracker.ietf.org/doc/html/rfc4861#section-4.4
    //
    // Using the Target link-layer address option defined at:
    // https://datatracker.ietf.org/doc/html/rfc4861#section-4.6.1
    constexpr size_t kIcmpv6OptionSize = 8;
    const int payload_size = sizeof(in6_addr) + kIcmpv6OptionSize;
    auto payload = std::make_unique<char[]>(payload_size);
    // Place the solicited IPv6 address at the beginning of the response payload
    memcpy(payload.get(), icmp6_payload, sizeof(in6_addr));
    // Setup the Target link-layer address option:
    //      0                   1                   2                   3
    //  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    // |     Type      |    Length     |    Link-Layer Address ...
    // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    int pos = sizeof(in6_addr);
    payload[pos++] = ND_OPT_TARGET_LINKADDR;  // Type
    payload[pos++] = 1;                       // Length in units of 8 octets
    memcpy(&payload[pos], eth_hdr_.h_source,
           ETH_ALEN);  // This interfaces' MAC address

    // Populate the ICMPv6 header
    icmp6_hdr response_hdr{};
    response_hdr.icmp6_type = ND_NEIGHBOR_ADVERT;
    // Set the solicited bit to true
    response_hdr.icmp6_dataun.icmp6_un_data8[0] = 64;
    // Craft the full ICMPv6 packet and then ship it off to WritePacket
    // to have it frame it with L2 headers and send it back to the requesting
    // neighbor.
    CreateIcmpPacket(ip_hdr->ip6_src, ip_hdr->ip6_src, response_hdr,
                     absl::string_view(payload.get(), payload_size),
                     [this](absl::string_view packet) {
                       WritePacketToNetwork(packet.data(), packet.size());
                     });
    return L2ValidationResult::kValidLinkLocal;
  }

  return L2ValidationResult::kValidNormal;
}

}  // namespace quic