system-proxy/proxy_connect_job.cc

// Copyright 2020 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 "system-proxy/proxy_connect_job.h"

#include <algorithm>
#include <utility>
#include <vector>

#include <curl/curl.h>
#include <curl/easy.h>

#include <base/base64.h>
#include <base/bind.h>
#include <base/bind_helpers.h>
#include <base/callback_helpers.h>
#include <base/files/file_util.h>
#include <base/strings/stringprintf.h>
#include <base/strings/string_split.h>
#include <base/strings/string_util.h>
#include <base/time/time.h>
#include <base/threading/thread.h>
#include <base/threading/thread_task_runner_handle.h>
#include <brillo/http/http_transport.h>
#include <chromeos/patchpanel/net_util.h>
#include <chromeos/patchpanel/socket.h>
#include <chromeos/patchpanel/socket_forwarder.h>

#include "system-proxy/curl_socket.h"

// The libarcnetwork-util library overloads << for socket data structures.
// By C++'s argument-dependent lookup rules, operators defined in a
// different namespace are not visible. We need the using directive to make
// the overload available this namespace.
using patchpanel::operator<<;

namespace {
// There's no RFC recomandation for the max size of http request headers but
// popular http server implementations (Apache, IIS, Tomcat) set the lower limit
// to 8000.
constexpr int kMaxHttpRequestHeadersSize = 8000;
constexpr char kConnectMethod[] = "CONNECT";
constexpr base::TimeDelta kCurlConnectTimeout = base::TimeDelta::FromMinutes(2);
constexpr base::TimeDelta kWaitClientConnectTimeout =
    base::TimeDelta::FromMinutes(2);
constexpr size_t kMaxBadRequestPrintSize = 120;
// This sequence is used to identify the end of a HTTP header which should be an
// empty line. Note: all HTTP header lines end with CRLF. HTTP connect requests
// don't have a body so end of header is end of request.
const std::string_view kCrlfCrlf = "\r\n\r\n";

// HTTP error codes and messages with origin information for debugging (RFC723,
// section 6.1).
const std::string_view kHttpBadRequest =
    "HTTP/1.1 400 Bad Request - Origin: local proxy\r\n\r\n";
const std::string_view kHttpConnectionTimeout =
    "HTTP/1.1 408 Request Timeout - Origin: local proxy\r\n\r\n";
const std::string_view kHttpInternalServerError =
    "HTTP/1.1 500 Internal Server Error - Origin: local proxy\r\n\r\n";
const std::string_view kHttpBadGateway =
    "HTTP/1.1 502 Bad Gateway - Origin: local proxy\r\n\r\n";

// Verifies if the http headers are ending with an http empty line, meaning a
// line that contains only CR LF preceded by a line ending with CRLF.
bool IsEndingWithHttpEmptyLine(const char* headers, int headers_size) {
  return headers_size > kCrlfCrlf.size() &&
         std::memcmp(kCrlfCrlf.data(),
                     headers + headers_size - kCrlfCrlf.size(),
                     kCrlfCrlf.size()) == 0;
}

// CURLOPT_HEADERFUNCTION callback implementation that only returns the headers
// from the last response sent by the sever. This is to make sure that we
// send back valid HTTP replies and auhentication data from the HTTP messages is
// not being leaked to the client. |userdata| is set on the libcurl CURL handle
// used to configure the request, using the the CURLOPT_HEADERDATA option. Note,
// from the libcurl documentation: This callback is being called for all the
// responses received from the proxy server after intiating the connection
// request. Multiple responses can be received in an authentication sequence.
// Only the last response's headers should be forwarded to the System-proxy
// client. The header callback will be called once for each header and only
// complete header lines are passed on to the callback.
static size_t WriteHeadersCallback(char* contents,
                                   size_t size,
                                   size_t nmemb,
                                   void* userdata) {
  std::vector<char>* vec = (std::vector<char>*)userdata;

  // Check if we are receiving a new HTTP message (after the last one was
  // terminated with an empty line).
  if (IsEndingWithHttpEmptyLine(vec->data(), vec->size())) {
    VLOG(1) << "Removing the http reply headers from the server "
            << base::StringPiece(vec->data(), vec->size());
    vec->clear();
  }
  vec->insert(vec->end(), contents, contents + (nmemb * size));
  return size * nmemb;
}

// CONNECT requests may have a reply body. This method will capture the reply
// and save it in |userdata|. |userdata| is set on the libcurl CURL handle
// used to configure the request, using the the CURLOPT_WRITEDATA option.
static size_t WriteCallback(char* contents,
                            size_t size,
                            size_t nmemb,
                            void* userdata) {
  std::vector<char>* vec = (std::vector<char>*)userdata;
  vec->insert(vec->end(), contents, contents + (nmemb * size));
  return size * nmemb;
}

// Parses the first line of the http CONNECT request and extracts the URI
// authority, defined in RFC3986, section 3.2, as the host name and port number
// separated by a colon. The destination URI is specified in the request line
// (RFC2817, section 5.2):
//      CONNECT server.example.com:80 HTTP/1.1
// If the first line in |raw_request| (the Request-Line) is a correctly formed
// CONNECT request, it will return the destination URI as host:port, otherwise
// it will return an empty string.
std::string GetUriAuthorityFromHttpHeader(
    const std::vector<char>& raw_request) {
  base::StringPiece request(raw_request.data(), raw_request.size());
  // Request-Line ends with CRLF (RFC2616, section 5.1).
  size_t i = request.find_first_of("\r\n");
  if (i == base::StringPiece::npos)
    return std::string();
  // Elements are delimited by non-breaking space (SP).
  auto pieces =
      base::SplitString(request.substr(0, i), " ", base::TRIM_WHITESPACE,
                        base::SPLIT_WANT_NONEMPTY);
  // Request-Line has the format: Method SP Request-URI SP HTTP-Version CRLF.
  if (pieces.size() < 3)
    return std::string();
  if (pieces[0] != kConnectMethod)
    return std::string();

  return pieces[1];
}
}  // namespace

namespace system_proxy {

ProxyConnectJob::ProxyConnectJob(
    std::unique_ptr<patchpanel::Socket> socket,
    const std::string& credentials,
    ResolveProxyCallback resolve_proxy_callback,
    OnConnectionSetupFinishedCallback setup_finished_callback)
    : credentials_(credentials),
      resolve_proxy_callback_(std::move(resolve_proxy_callback)),
      setup_finished_callback_(std::move(setup_finished_callback)),
      // Safe to use |base::Unretained| because the callback will be canceled
      // when it goes out of scope.
      client_connect_timeout_callback_(base::Bind(
          &ProxyConnectJob::OnClientConnectTimeout, base::Unretained(this))) {
  client_socket_ = std::move(socket);
}

ProxyConnectJob::~ProxyConnectJob() = default;

bool ProxyConnectJob::Start() {
  // Make the socket non-blocking.
  if (!base::SetNonBlocking(client_socket_->fd())) {
    PLOG(ERROR) << *this << " Failed to mark the socket as non-blocking.";
    client_socket_->SendTo(kHttpInternalServerError.data(),
                           kHttpInternalServerError.size());
    return false;
  }
  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
      FROM_HERE, client_connect_timeout_callback_.callback(),
      kWaitClientConnectTimeout);
  read_watcher_ = base::FileDescriptorWatcher::WatchReadable(
      client_socket_->fd(),
      base::Bind(&ProxyConnectJob::OnClientReadReady, base::Unretained(this)));
  return true;
}

void ProxyConnectJob::OnClientReadReady() {
  if (!read_watcher_) {
    // The connection has timed out while waiting for the client's HTTP CONNECT
    // request. See |OnClientConnectTimeout|.
    return;
  }
  client_connect_timeout_callback_.Cancel();
  // Stop watching.
  read_watcher_.reset();
  // The first message should be a HTTP CONNECT request.
  std::vector<char> connect_request;
  if (!TryReadHttpHeader(&connect_request)) {
    std::string encoded;
    base::Base64Encode(
        base::StringPiece(connect_request.data(), connect_request.size()),
        &encoded);
    LOG(ERROR) << *this
               << " Failure to read proxy CONNECT request. Base 64 encoded "
                  "request message from client: "
               << encoded;
    OnError(kHttpBadRequest);
    return;
  }

  target_url_ = GetUriAuthorityFromHttpHeader(connect_request);
  if (target_url_.empty()) {
    LOG(ERROR)
        << *this
        << " Failed to extract target url from the HTTP CONNECT request.";
    OnError(kHttpBadRequest);
    return;
  }

  // The proxy resolution service in Chrome expects a proper URL, formatted as
  // scheme://host:port. It's safe to assume only https will be used for the
  // target url.
  std::move(resolve_proxy_callback_)
      .Run(base::StringPrintf("https://%s", target_url_.c_str()),
           base::Bind(&ProxyConnectJob::OnProxyResolution,
                      base::Unretained(this)));
}

bool ProxyConnectJob::TryReadHttpHeader(std::vector<char>* raw_request) {
  size_t read_byte_count = 0;
  raw_request->resize(kMaxHttpRequestHeadersSize);

  // Read byte-by-byte and stop when reading an empty line (only CRLF) or when
  // exceeding the max buffer size.
  // TODO(acostinas, chromium:1064536) This may have some measurable performance
  // impact. We should read larger blocks of data, consume the HTTP headers,
  // cache the tunneled payload that may have already been included (e.g. TLS
  // ClientHello) and send it to server after the connection is established.
  while (read_byte_count < kMaxHttpRequestHeadersSize) {
    if (client_socket_->RecvFrom(raw_request->data() + read_byte_count, 1) <=
        0) {
      raw_request->resize(std::min(read_byte_count, kMaxBadRequestPrintSize));
      return false;
    }
    ++read_byte_count;

    if (IsEndingWithHttpEmptyLine(raw_request->data(), read_byte_count)) {
      raw_request->resize(read_byte_count);
      return true;
    }
  }
  return false;
}

void ProxyConnectJob::OnProxyResolution(
    const std::list<std::string>& proxy_servers) {
  proxy_servers_ = proxy_servers;
  DoCurlServerConnection(proxy_servers.front());
}

void ProxyConnectJob::DoCurlServerConnection(const std::string& proxy_url) {
  CURL* easyhandle = curl_easy_init();
  CURLcode res;
  curl_socket_t newSocket = -1;
  std::vector<char> server_header_reply, server_body_reply;

  if (!easyhandle) {
    // Unfortunately it's not possible to get the failure reason.
    LOG(ERROR) << *this << " Failure to create curl handle.";
    curl_easy_cleanup(easyhandle);
    OnError(kHttpInternalServerError);
    return;
  }
  curl_easy_setopt(easyhandle, CURLOPT_URL, target_url_.c_str());

  if (proxy_url != brillo::http::kDirectProxy) {
    curl_easy_setopt(easyhandle, CURLOPT_PROXY, proxy_url.c_str());
    curl_easy_setopt(easyhandle, CURLOPT_HTTPPROXYTUNNEL, 1L);
    curl_easy_setopt(easyhandle, CURLOPT_CONNECT_ONLY, 1);
    // Allow libcurl to pick authentication method. Curl will use the most
    // secure one the remote site claims to support.
    curl_easy_setopt(easyhandle, CURLOPT_PROXYAUTH, CURLAUTH_ANY);
    curl_easy_setopt(easyhandle, CURLOPT_PROXYUSERPWD, credentials_.c_str());
  }
  curl_easy_setopt(easyhandle, CURLOPT_CONNECTTIMEOUT_MS,
                   kCurlConnectTimeout.InMilliseconds());
  curl_easy_setopt(easyhandle, CURLOPT_HEADERFUNCTION, WriteHeadersCallback);
  curl_easy_setopt(easyhandle, CURLOPT_HEADERDATA, &server_header_reply);
  curl_easy_setopt(easyhandle, CURLOPT_WRITEFUNCTION, WriteCallback);
  curl_easy_setopt(easyhandle, CURLOPT_WRITEDATA, &server_body_reply);

  res = curl_easy_perform(easyhandle);

  if (res != CURLE_OK) {
    LOG(ERROR) << *this << " curl_easy_perform() failed with error: ",
        curl_easy_strerror(res);
    curl_easy_cleanup(easyhandle);

    if (server_header_reply.size() > 0) {
      // Send the error message from the remote server back to the client.
      OnError(std::string_view(server_header_reply.data(),
                               server_header_reply.size()));
    } else {
      OnError(kHttpInternalServerError);
    }
    return;
  }
  // Extract the socket from the curl handle.
  res = curl_easy_getinfo(easyhandle, CURLINFO_ACTIVESOCKET, &newSocket);
  if (res != CURLE_OK) {
    LOG(ERROR) << *this << " Failed to get socket from curl with error: "
               << curl_easy_strerror(res);
    curl_easy_cleanup(easyhandle);
    OnError(kHttpBadGateway);
    return;
  }

  ScopedCurlEasyhandle scoped_handle(easyhandle, FreeCurlEasyhandle());
  auto server_conn = std::make_unique<CurlSocket>(base::ScopedFD(newSocket),
                                                  std::move(scoped_handle));

  // Send the server reply to the client. If the connection is successful, the
  // reply headers should be "HTTP/1.1 200 Connection Established".
  if (client_socket_->SendTo(server_header_reply.data(),
                             server_header_reply.size()) !=
      server_header_reply.size()) {
    PLOG(ERROR) << *this << " Failed to send HTTP reply headers to client: "
                << base::StringPiece(server_header_reply.data(),
                                     server_header_reply.size());
    OnError(kHttpInternalServerError);
    return;
  }
  // HTTP CONNECT responses can have a payload body which should be forwarded to
  // the client.
  if (server_body_reply.size() > 0) {
    // TODO(acostinas, chromium:1064536) Resend the reply body in case of EAGAIN
    // or EWOULDBLOCK errors.
    if (client_socket_->SendTo(server_body_reply.data(),
                               server_body_reply.size()) !=
        server_body_reply.size()) {
      PLOG(ERROR) << *this
                  << " Failed to send HTTP CONNECT reply body to client: "
                  << base::StringPiece(server_body_reply.data(),
                                       server_body_reply.size());
    }
  }

  auto fwd = std::make_unique<patchpanel::SocketForwarder>(
      base::StringPrintf("%d-%d", client_socket_->fd(), server_conn->fd()),
      std::move(client_socket_), std::move(server_conn));
  // Start forwarding data between sockets.
  fwd->Start();
  std::move(setup_finished_callback_).Run(std::move(fwd), this);
}

void ProxyConnectJob::OnError(const std::string_view& http_error_message) {
  client_socket_->SendTo(http_error_message.data(), http_error_message.size());
  std::move(setup_finished_callback_).Run(nullptr, this);
}

void ProxyConnectJob::OnClientConnectTimeout() {
  // Stop listening for client connect requests.
  read_watcher_.reset();
  LOG(ERROR) << *this
             << " Connection timed out while waiting for the client to send a "
                "connect request.";
  OnError(kHttpConnectionTimeout);
}

std::ostream& operator<<(std::ostream& stream, const ProxyConnectJob& job) {
  stream << "{fd: " << job.client_socket_->fd();
  if (!job.target_url_.empty()) {
    stream << ", url: " << job.target_url_;
  }
  stream << "}";
  return stream;
}

}  // namespace system_proxy