breakpad/src/client/linux/crash_generation/crash_generation_server.cc

// Copyright (c) 2010 Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include <assert.h>
#include <dirent.h>
#include <fcntl.h>
#include <limits.h>
#include <poll.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <vector>

#include "client/linux/crash_generation/crash_generation_server.h"
#include "client/linux/crash_generation/client_info.h"
#include "client/linux/handler/exception_handler.h"
#include "client/linux/minidump_writer/minidump_writer.h"
#include "common/linux/eintr_wrapper.h"
#include "common/linux/guid_creator.h"
#include "common/linux/safe_readlink.h"

static const char kCommandQuit = 'x';

static bool
GetInodeForFileDescriptor(ino_t* inode_out, int fd)
{
  assert(inode_out);

  struct stat buf;
  if (fstat(fd, &buf) < 0)
    return false;

  if (!S_ISSOCK(buf.st_mode))
    return false;

  *inode_out = buf.st_ino;
  return true;
}

// expected prefix of the target of the /proc/self/fd/%d link for a socket
static const char kSocketLinkPrefix[] = "socket:[";

// Parse a symlink in /proc/pid/fd/$x and return the inode number of the
// socket.
//   inode_out: (output) set to the inode number on success
//   path: e.g. /proc/1234/fd/5 (must be a UNIX domain socket descriptor)
static bool
GetInodeForProcPath(ino_t* inode_out, const char* path)
{
  assert(inode_out);
  assert(path);

  char buf[PATH_MAX];
  if (!google_breakpad::SafeReadLink(path, buf)) {
    return false;
  }

  if (0 != memcmp(kSocketLinkPrefix, buf, sizeof(kSocketLinkPrefix) - 1)) {
    return false;
  }

  char* endptr;
  const uint64_t inode_ul =
      strtoull(buf + sizeof(kSocketLinkPrefix) - 1, &endptr, 10);
  if (*endptr != ']')
    return false;

  if (inode_ul == ULLONG_MAX) {
    return false;
  }

  *inode_out = inode_ul;
  return true;
}

static bool
FindProcessHoldingSocket(pid_t* pid_out, ino_t socket_inode)
{
  assert(pid_out);
  bool already_found = false;

  DIR* proc = opendir("/proc");
  if (!proc) {
    return false;
  }

  std::vector<pid_t> pids;

  struct dirent* dent;
  while ((dent = readdir(proc))) {
    char* endptr;
    const unsigned long int pid_ul = strtoul(dent->d_name, &endptr, 10);
    if (pid_ul == ULONG_MAX || '\0' != *endptr)
      continue;
    pids.push_back(pid_ul);
  }
  closedir(proc);

  for (std::vector<pid_t>::const_iterator
       i = pids.begin(); i != pids.end(); ++i) {
    const pid_t current_pid = *i;
    char buf[PATH_MAX];
    snprintf(buf, sizeof(buf), "/proc/%d/fd", current_pid);
    DIR* fd = opendir(buf);
    if (!fd)
      continue;

    while ((dent = readdir(fd))) {
      if (snprintf(buf, sizeof(buf), "/proc/%d/fd/%s", current_pid,
                   dent->d_name) >= static_cast<int>(sizeof(buf))) {
        continue;
      }

      ino_t fd_inode;
      if (GetInodeForProcPath(&fd_inode, buf)
          && fd_inode == socket_inode) {
        if (already_found) {
          closedir(fd);
          return false;
        }

        already_found = true;
        *pid_out = current_pid;
        break;
      }
    }

    closedir(fd);
  }

  return already_found;
}

namespace google_breakpad {

CrashGenerationServer::CrashGenerationServer(
  const int listen_fd,
  OnClientDumpRequestCallback dump_callback,
  void* dump_context,
  OnClientExitingCallback exit_callback,
  void* exit_context,
  bool generate_dumps,
  const string* dump_path) :
    server_fd_(listen_fd),
    dump_callback_(dump_callback),
    dump_context_(dump_context),
    exit_callback_(exit_callback),
    exit_context_(exit_context),
    generate_dumps_(generate_dumps),
    started_(false)
{
  if (dump_path)
    dump_dir_ = *dump_path;
  else
    dump_dir_ = "/tmp";
}

CrashGenerationServer::~CrashGenerationServer()
{
  if (started_)
    Stop();
}

bool
CrashGenerationServer::Start()
{
  if (started_ || 0 > server_fd_)
    return false;

  int control_pipe[2];
  if (pipe(control_pipe))
    return false;

  if (fcntl(control_pipe[0], F_SETFD, FD_CLOEXEC))
    return false;
  if (fcntl(control_pipe[1], F_SETFD, FD_CLOEXEC))
    return false;

  if (fcntl(control_pipe[0], F_SETFL, O_NONBLOCK))
    return false;

  control_pipe_in_ = control_pipe[0];
  control_pipe_out_ = control_pipe[1];

  if (pthread_create(&thread_, NULL,
                     ThreadMain, reinterpret_cast<void*>(this)))
    return false;

  started_ = true;
  return true;
}

void
CrashGenerationServer::Stop()
{
  assert(pthread_self() != thread_);

  if (!started_)
    return;

  HANDLE_EINTR(write(control_pipe_out_, &kCommandQuit, 1));

  void* dummy;
  pthread_join(thread_, &dummy);

  started_ = false;
}

//static
bool
CrashGenerationServer::CreateReportChannel(int* server_fd, int* client_fd)
{
  int fds[2];

  if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, fds))
    return false;

  static const int on = 1;
  // Enable passcred on the server end of the socket
  if (setsockopt(fds[1], SOL_SOCKET, SO_PASSCRED, &on, sizeof(on)))
    return false;

  if (fcntl(fds[1], F_SETFL, O_NONBLOCK))
    return false;
  if (fcntl(fds[1], F_SETFD, FD_CLOEXEC))
    return false;

  *client_fd = fds[0];
  *server_fd = fds[1];
  return true;
}

// The following methods/functions execute on the server thread

void
CrashGenerationServer::Run()
{
  struct pollfd pollfds[2];
  memset(&pollfds, 0, sizeof(pollfds));

  pollfds[0].fd = server_fd_;
  pollfds[0].events = POLLIN;

  pollfds[1].fd = control_pipe_in_;
  pollfds[1].events = POLLIN;

  while (true) {
    // infinite timeout
    int nevents = poll(pollfds, sizeof(pollfds)/sizeof(pollfds[0]), -1);
    if (-1 == nevents) {
      if (EINTR == errno) {
        continue;
      } else {
        return;
      }
    }

    if (pollfds[0].revents && !ClientEvent(pollfds[0].revents))
      return;

    if (pollfds[1].revents && !ControlEvent(pollfds[1].revents))
      return;
  }
}

bool
CrashGenerationServer::ClientEvent(short revents)
{
  if (POLLHUP & revents)
    return false;
  assert(POLLIN & revents);

  // A process has crashed and has signaled us by writing a datagram
  // to the death signal socket. The datagram contains the crash context needed
  // for writing the minidump as well as a file descriptor and a credentials
  // block so that they can't lie about their pid.

  // The length of the control message:
  static const unsigned kControlMsgSize =
      CMSG_SPACE(sizeof(int)) + CMSG_SPACE(sizeof(struct ucred));
  // The length of the regular payload:
  static const unsigned kCrashContextSize =
      sizeof(google_breakpad::ExceptionHandler::CrashContext);

  struct msghdr msg = {0};
  struct iovec iov[1];
  char crash_context[kCrashContextSize];
  char control[kControlMsgSize];
  const ssize_t expected_msg_size = sizeof(crash_context);

  iov[0].iov_base = crash_context;
  iov[0].iov_len = sizeof(crash_context);
  msg.msg_iov = iov;
  msg.msg_iovlen = sizeof(iov)/sizeof(iov[0]);
  msg.msg_control = control;
  msg.msg_controllen = kControlMsgSize;

  const ssize_t msg_size = HANDLE_EINTR(recvmsg(server_fd_, &msg, 0));
  if (msg_size != expected_msg_size)
    return true;

  if (msg.msg_controllen != kControlMsgSize ||
      msg.msg_flags & ~MSG_TRUNC)
    return true;

  // Walk the control payload and extract the file descriptor and validated pid.
  pid_t crashing_pid = -1;
  int signal_fd = -1;
  for (struct cmsghdr *hdr = CMSG_FIRSTHDR(&msg); hdr;
       hdr = CMSG_NXTHDR(&msg, hdr)) {
    if (hdr->cmsg_level != SOL_SOCKET)
      continue;
    if (hdr->cmsg_type == SCM_RIGHTS) {
      const unsigned len = hdr->cmsg_len -
          (((uint8_t*)CMSG_DATA(hdr)) - (uint8_t*)hdr);
      assert(len % sizeof(int) == 0u);
      const unsigned num_fds = len / sizeof(int);
      if (num_fds > 1 || num_fds == 0) {
        // A nasty process could try and send us too many descriptors and
        // force a leak.
        for (unsigned i = 0; i < num_fds; ++i)
          close(reinterpret_cast<int*>(CMSG_DATA(hdr))[i]);
        return true;
      } else {
        signal_fd = reinterpret_cast<int*>(CMSG_DATA(hdr))[0];
      }
    } else if (hdr->cmsg_type == SCM_CREDENTIALS) {
      const struct ucred *cred =
          reinterpret_cast<struct ucred*>(CMSG_DATA(hdr));
      crashing_pid = cred->pid;
    }
  }

  if (crashing_pid == -1 || signal_fd == -1) {
    if (signal_fd)
      close(signal_fd);
    return true;
  }

  // Kernel bug workaround (broken in 2.6.30 at least):
  // The kernel doesn't translate PIDs in SCM_CREDENTIALS across PID
  // namespaces. Thus |crashing_pid| might be garbage from our point of view.
  // In the future we can remove this workaround, but we have to wait a couple
  // of years to be sure that it's worked its way out into the world.

  ino_t inode_number;
  if (!GetInodeForFileDescriptor(&inode_number, signal_fd)) {
    close(signal_fd);
    return true;
  }

  if (!FindProcessHoldingSocket(&crashing_pid, inode_number - 1)) {
    close(signal_fd);
    return true;
  }

  string minidump_filename;
  if (!MakeMinidumpFilename(minidump_filename))
    return true;

  if (!google_breakpad::WriteMinidump(minidump_filename.c_str(),
                                      crashing_pid, crash_context,
                                      kCrashContextSize)) {
    close(signal_fd);
    return true;
  }

  if (dump_callback_) {
    ClientInfo info(crashing_pid, this);

    dump_callback_(dump_context_, &info, &minidump_filename);
  }

  // Send the done signal to the process: it can exit now.
  memset(&msg, 0, sizeof(msg));
  struct iovec done_iov;
  done_iov.iov_base = const_cast<char*>("\x42");
  done_iov.iov_len = 1;
  msg.msg_iov = &done_iov;
  msg.msg_iovlen = 1;

  HANDLE_EINTR(sendmsg(signal_fd, &msg, MSG_DONTWAIT | MSG_NOSIGNAL));
  close(signal_fd);

  return true;
}

bool
CrashGenerationServer::ControlEvent(short revents)
{
  if (POLLHUP & revents)
    return false;
  assert(POLLIN & revents);

  char command;
  if (read(control_pipe_in_, &command, 1))
    return false;

  switch (command) {
  case kCommandQuit:
    return false;
  default:
    assert(0);
  }

  return true;
}

bool
CrashGenerationServer::MakeMinidumpFilename(string& outFilename)
{
  GUID guid;
  char guidString[kGUIDStringLength+1];

  if (!(CreateGUID(&guid)
        && GUIDToString(&guid, guidString, sizeof(guidString))))
    return false;

  char path[PATH_MAX];
  snprintf(path, sizeof(path), "%s/%s.dmp", dump_dir_.c_str(), guidString);

  outFilename = path;
  return true;
}

// static
void*
CrashGenerationServer::ThreadMain(void *arg)
{
  reinterpret_cast<CrashGenerationServer*>(arg)->Run();
  return NULL;
}

}  // namespace google_breakpad