content/zygote/zygote_linux.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/zygote/zygote_linux.h"
   6
   7 #include <fcntl.h>
   8 #include <string.h>
   9 #include <sys/socket.h>
  10 #include <sys/types.h>
  11 #include <sys/wait.h>
  12
  13 #include "base/command_line.h"
  14 #include "base/debug/trace_event.h"
  15 #include "base/files/file_util.h"
  16 #include "base/linux_util.h"
  17 #include "base/logging.h"
  18 #include "base/macros.h"
  19 #include "base/memory/scoped_vector.h"
  20 #include "base/pickle.h"
  21 #include "base/posix/eintr_wrapper.h"
  22 #include "base/posix/global_descriptors.h"
  23 #include "base/posix/unix_domain_socket_linux.h"
  24 #include "base/process/kill.h"
  25 #include "content/common/child_process_sandbox_support_impl_linux.h"
  26 #include "content/common/sandbox_linux/sandbox_linux.h"
  27 #include "content/common/set_process_title.h"
  28 #include "content/common/zygote_commands_linux.h"
  29 #include "content/public/common/content_descriptors.h"
  30 #include "content/public/common/result_codes.h"
  31 #include "content/public/common/sandbox_linux.h"
  32 #include "content/public/common/send_zygote_child_ping_linux.h"
  33 #include "content/public/common/zygote_fork_delegate_linux.h"
  34 #include "ipc/ipc_channel.h"
  35 #include "ipc/ipc_switches.h"
  36 #include "sandbox/linux/services/syscall_wrappers.h"
  37
  38 #if defined(ADDRESS_SANITIZER)
  39 #include <sanitizer/asan_interface.h>
  40 #endif
  41
  42 // See http://code.google.com/p/chromium/wiki/LinuxZygote
  43
  44 namespace content {
  45
  46 namespace {
  47
  48 // NOP function. See below where this handler is installed.
  49 void SIGCHLDHandler(int signal) {
  50 }
  51
  52 int LookUpFd(const base::GlobalDescriptors::Mapping& fd_mapping, uint32_t key) {
  53   for (size_t index = 0; index < fd_mapping.size(); ++index) {
  54     if (fd_mapping[index].key == key)
  55       return fd_mapping[index].fd;
  56   }
  57   return -1;
  58 }
  59
  60 void CreatePipe(base::ScopedFD* read_pipe, base::ScopedFD* write_pipe) {
  61   int raw_pipe[2];
  62   PCHECK(0 == pipe(raw_pipe));
  63   read_pipe->reset(raw_pipe[0]);
  64   write_pipe->reset(raw_pipe[1]);
  65 }
  66
  67 void KillAndReap(pid_t pid, ZygoteForkDelegate* helper) {
  68   if (helper) {
  69     // Helper children may be forked in another PID namespace, so |pid| might
  70     // be meaningless to us; or we just might not be able to directly send it
  71     // signals.  So we can't kill it.
  72     // Additionally, we're not its parent, so we can't reap it anyway.
  73     // TODO(mdempsky): Extend the ZygoteForkDelegate API to handle this.
  74     LOG(WARNING) << "Unable to kill or reap helper children";
  75     return;
  76   }
  77
  78   // Kill the child process in case it's not already dead, so we can safely
  79   // perform a blocking wait.
  80   PCHECK(0 == kill(pid, SIGKILL));
  81   PCHECK(pid == HANDLE_EINTR(waitpid(pid, NULL, 0)));
  82 }
  83
  84 }  // namespace
  85
  86 Zygote::Zygote(int sandbox_flags, ScopedVector<ZygoteForkDelegate> helpers,
  87                const std::vector<base::ProcessHandle>& extra_children,
  88                const std::vector<int>& extra_fds)
  89     : sandbox_flags_(sandbox_flags),
  90       helpers_(helpers.Pass()),
  91       initial_uma_index_(0),
  92       extra_children_(extra_children),
  93       extra_fds_(extra_fds) {}
  94
  95 Zygote::~Zygote() {
  96 }
  97
  98 bool Zygote::ProcessRequests() {
  99   // A SOCK_SEQPACKET socket is installed in fd 3. We get commands from the
 100   // browser on it.
 101   // A SOCK_DGRAM is installed in fd 5. This is the sandbox IPC channel.
 102   // See http://code.google.com/p/chromium/wiki/LinuxSandboxIPC
 103
 104   // We need to accept SIGCHLD, even though our handler is a no-op because
 105   // otherwise we cannot wait on children. (According to POSIX 2001.)
 106   struct sigaction action;
 107   memset(&action, 0, sizeof(action));
 108   action.sa_handler = &SIGCHLDHandler;
 109   CHECK(sigaction(SIGCHLD, &action, NULL) == 0);
 110
 111   if (UsingSUIDSandbox()) {
 112     // Let the ZygoteHost know we are ready to go.
 113     // The receiving code is in content/browser/zygote_host_linux.cc.
 114     bool r = UnixDomainSocket::SendMsg(kZygoteSocketPairFd,
 115                                        kZygoteHelloMessage,
 116                                        sizeof(kZygoteHelloMessage),
 117                                        std::vector<int>());
 118 #if defined(OS_CHROMEOS)
 119     LOG_IF(WARNING, !r) << "Sending zygote magic failed";
 120     // Exit normally on chromeos because session manager may send SIGTERM
 121     // right after the process starts and it may fail to send zygote magic
 122     // number to browser process.
 123     if (!r)
 124       _exit(RESULT_CODE_NORMAL_EXIT);
 125 #else
 126     CHECK(r) << "Sending zygote magic failed";
 127 #endif
 128   }
 129
 130   for (;;) {
 131     // This function call can return multiple times, once per fork().
 132     if (HandleRequestFromBrowser(kZygoteSocketPairFd))
 133       return true;
 134   }
 135 }
 136
 137 bool Zygote::GetProcessInfo(base::ProcessHandle pid,
 138                             ZygoteProcessInfo* process_info) {
 139   DCHECK(process_info);
 140   const ZygoteProcessMap::const_iterator it = process_info_map_.find(pid);
 141   if (it == process_info_map_.end()) {
 142     return false;
 143   }
 144   *process_info = it->second;
 145   return true;
 146 }
 147
 148 bool Zygote::UsingSUIDSandbox() const {
 149   return sandbox_flags_ & kSandboxLinuxSUID;
 150 }
 151
 152 bool Zygote::HandleRequestFromBrowser(int fd) {
 153   ScopedVector<base::ScopedFD> fds;
 154   char buf[kZygoteMaxMessageLength];
 155   const ssize_t len = UnixDomainSocket::RecvMsg(fd, buf, sizeof(buf), &fds);
 156
 157   if (len == 0 || (len == -1 && errno == ECONNRESET)) {
 158     // EOF from the browser. We should die.
 159     // TODO(earthdok): call __sanititizer_cov_dump() here to obtain code
 160     // coverage  for the Zygote. Currently it's not possible because of
 161     // confusion over who is responsible for closing the file descriptor.
 162     for (std::vector<int>::iterator it = extra_fds_.begin();
 163          it < extra_fds_.end(); ++it) {
 164       PCHECK(0 == IGNORE_EINTR(close(*it)));
 165     }
 166 #if !defined(ADDRESS_SANITIZER)
 167     // TODO(earthdok): add watchdog thread before using this in non-ASAN builds.
 168     CHECK(extra_children_.empty());
 169 #endif
 170     for (std::vector<base::ProcessHandle>::iterator it =
 171              extra_children_.begin();
 172          it < extra_children_.end(); ++it) {
 173       PCHECK(*it == HANDLE_EINTR(waitpid(*it, NULL, 0)));
 174     }
 175     _exit(0);
 176     return false;
 177   }
 178
 179   if (len == -1) {
 180     PLOG(ERROR) << "Error reading message from browser";
 181     return false;
 182   }
 183
 184   Pickle pickle(buf, len);
 185   PickleIterator iter(pickle);
 186
 187   int kind;
 188   if (iter.ReadInt(&kind)) {
 189     switch (kind) {
 190       case kZygoteCommandFork:
 191         // This function call can return multiple times, once per fork().
 192         return HandleForkRequest(fd, iter, fds.Pass());
 193
 194       case kZygoteCommandReap:
 195         if (!fds.empty())
 196           break;
 197         HandleReapRequest(fd, iter);
 198         return false;
 199       case kZygoteCommandGetTerminationStatus:
 200         if (!fds.empty())
 201           break;
 202         HandleGetTerminationStatus(fd, iter);
 203         return false;
 204       case kZygoteCommandGetSandboxStatus:
 205         HandleGetSandboxStatus(fd, iter);
 206         return false;
 207       case kZygoteCommandForkRealPID:
 208         // This shouldn't happen in practice, but some failure paths in
 209         // HandleForkRequest (e.g., if ReadArgsAndFork fails during depickling)
 210         // could leave this command pending on the socket.
 211         LOG(ERROR) << "Unexpected real PID message from browser";
 212         NOTREACHED();
 213         return false;
 214       default:
 215         NOTREACHED();
 216         break;
 217     }
 218   }
 219
 220   LOG(WARNING) << "Error parsing message from browser";
 221   return false;
 222 }
 223
 224 // TODO(jln): remove callers to this broken API. See crbug.com/274855.
 225 void Zygote::HandleReapRequest(int fd,
 226                                PickleIterator iter) {
 227   base::ProcessId child;
 228
 229   if (!iter.ReadInt(&child)) {
 230     LOG(WARNING) << "Error parsing reap request from browser";
 231     return;
 232   }
 233
 234   ZygoteProcessInfo child_info;
 235   if (!GetProcessInfo(child, &child_info)) {
 236     LOG(ERROR) << "Child not found!";
 237     NOTREACHED();
 238     return;
 239   }
 240
 241   if (!child_info.started_from_helper) {
 242     // Do not call base::EnsureProcessTerminated() under ThreadSanitizer, as it
 243     // spawns a separate thread which may live until the call to fork() in the
 244     // zygote. As a result, ThreadSanitizer will report an error and almost
 245     // disable race detection in the child process.
 246     // Not calling EnsureProcessTerminated() may result in zombie processes
 247     // sticking around. This will only happen during testing, so we can live
 248     // with this for now.
 249 #if !defined(THREAD_SANITIZER)
 250     // TODO(jln): this old code is completely broken. See crbug.com/274855.
 251     base::EnsureProcessTerminated(base::Process(child_info.internal_pid));
 252 #else
 253     LOG(WARNING) << "Zygote process omitting a call to "
 254         << "base::EnsureProcessTerminated() for child pid " << child
 255         << " under ThreadSanitizer. See http://crbug.com/274855.";
 256 #endif
 257   } else {
 258     // For processes from the helper, send a GetTerminationStatus request
 259     // with known_dead set to true.
 260     // This is not perfect, as the process may be killed instantly, but is
 261     // better than ignoring the request.
 262     base::TerminationStatus status;
 263     int exit_code;
 264     bool got_termination_status =
 265         GetTerminationStatus(child, true /* known_dead */, &status, &exit_code);
 266     DCHECK(got_termination_status);
 267   }
 268   process_info_map_.erase(child);
 269 }
 270
 271 bool Zygote::GetTerminationStatus(base::ProcessHandle real_pid,
 272                                   bool known_dead,
 273                                   base::TerminationStatus* status,
 274                                   int* exit_code) {
 275
 276   ZygoteProcessInfo child_info;
 277   if (!GetProcessInfo(real_pid, &child_info)) {
 278     LOG(ERROR) << "Zygote::GetTerminationStatus for unknown PID "
 279                << real_pid;
 280     NOTREACHED();
 281     return false;
 282   }
 283   // We know about |real_pid|.
 284   const base::ProcessHandle child = child_info.internal_pid;
 285   if (child_info.started_from_helper) {
 286     if (!child_info.started_from_helper->GetTerminationStatus(
 287             child, known_dead, status, exit_code)) {
 288       return false;
 289     }
 290   } else {
 291     // Handle the request directly.
 292     if (known_dead) {
 293       *status = base::GetKnownDeadTerminationStatus(child, exit_code);
 294     } else {
 295       // We don't know if the process is dying, so get its status but don't
 296       // wait.
 297       *status = base::GetTerminationStatus(child, exit_code);
 298     }
 299   }
 300   // Successfully got a status for |real_pid|.
 301   if (*status != base::TERMINATION_STATUS_STILL_RUNNING) {
 302     // Time to forget about this process.
 303     process_info_map_.erase(real_pid);
 304   }
 305   return true;
 306 }
 307
 308 void Zygote::HandleGetTerminationStatus(int fd,
 309                                         PickleIterator iter) {
 310   bool known_dead;
 311   base::ProcessHandle child_requested;
 312
 313   if (!iter.ReadBool(&known_dead) || !iter.ReadInt(&child_requested)) {
 314     LOG(WARNING) << "Error parsing GetTerminationStatus request "
 315                  << "from browser";
 316     return;
 317   }
 318
 319   base::TerminationStatus status;
 320   int exit_code;
 321
 322   bool got_termination_status =
 323       GetTerminationStatus(child_requested, known_dead, &status, &exit_code);
 324   if (!got_termination_status) {
 325     // Assume that if we can't find the child in the sandbox, then
 326     // it terminated normally.
 327     NOTREACHED();
 328     status = base::TERMINATION_STATUS_NORMAL_TERMINATION;
 329     exit_code = RESULT_CODE_NORMAL_EXIT;
 330   }
 331
 332   Pickle write_pickle;
 333   write_pickle.WriteInt(static_cast<int>(status));
 334   write_pickle.WriteInt(exit_code);
 335   ssize_t written =
 336       HANDLE_EINTR(write(fd, write_pickle.data(), write_pickle.size()));
 337   if (written != static_cast<ssize_t>(write_pickle.size()))
 338     PLOG(ERROR) << "write";
 339 }
 340
 341 int Zygote::ForkWithRealPid(const std::string& process_type,
 342                             const base::GlobalDescriptors::Mapping& fd_mapping,
 343                             const std::string& channel_id,
 344                             base::ScopedFD pid_oracle,
 345                             std::string* uma_name,
 346                             int* uma_sample,
 347                             int* uma_boundary_value) {
 348   ZygoteForkDelegate* helper = NULL;
 349   for (ScopedVector<ZygoteForkDelegate>::iterator i = helpers_.begin();
 350        i != helpers_.end();
 351        ++i) {
 352     if ((*i)->CanHelp(process_type, uma_name, uma_sample, uma_boundary_value)) {
 353       helper = *i;
 354       break;
 355     }
 356   }
 357
 358   base::ScopedFD read_pipe, write_pipe;
 359   base::ProcessId pid = 0;
 360   if (helper) {
 361     int ipc_channel_fd = LookUpFd(fd_mapping, kPrimaryIPCChannel);
 362     if (ipc_channel_fd < 0) {
 363       DLOG(ERROR) << "Failed to find kPrimaryIPCChannel in FD mapping";
 364       return -1;
 365     }
 366     std::vector<int> fds;
 367     fds.push_back(ipc_channel_fd);  // kBrowserFDIndex
 368     fds.push_back(pid_oracle.get());  // kPIDOracleFDIndex
 369     pid = helper->Fork(process_type, fds, channel_id);
 370
 371     // Helpers should never return in the child process.
 372     CHECK_NE(pid, 0);
 373   } else {
 374     CreatePipe(&read_pipe, &write_pipe);
 375     // This is roughly equivalent to a fork(). We are using ForkWithFlags mainly
 376     // to give it some more diverse test coverage.
 377     pid = base::ForkWithFlags(SIGCHLD, nullptr, nullptr);
 378   }
 379
 380   if (pid == 0) {
 381     // In the child process.
 382     write_pipe.reset();
 383
 384     // Ping the PID oracle socket so the browser can find our PID.
 385     CHECK(SendZygoteChildPing(pid_oracle.get()));
 386
 387     // Now read back our real PID from the zygote.
 388     base::ProcessId real_pid;
 389     if (!base::ReadFromFD(read_pipe.get(),
 390                           reinterpret_cast<char*>(&real_pid),
 391                           sizeof(real_pid))) {
 392       LOG(FATAL) << "Failed to synchronise with parent zygote process";
 393     }
 394     if (real_pid <= 0) {
 395       LOG(FATAL) << "Invalid pid from parent zygote";
 396     }
 397 #if defined(OS_LINUX)
 398     // Sandboxed processes need to send the global, non-namespaced PID when
 399     // setting up an IPC channel to their parent.
 400     IPC::Channel::SetGlobalPid(real_pid);
 401     // Force the real PID so chrome event data have a PID that corresponds
 402     // to system trace event data.
 403     base::debug::TraceLog::GetInstance()->SetProcessID(
 404         static_cast<int>(real_pid));
 405 #endif
 406     return 0;
 407   }
 408
 409   // In the parent process.
 410   read_pipe.reset();
 411   pid_oracle.reset();
 412
 413   // Always receive a real PID from the zygote host, though it might
 414   // be invalid (see below).
 415   base::ProcessId real_pid;
 416   {
 417     ScopedVector<base::ScopedFD> recv_fds;
 418     char buf[kZygoteMaxMessageLength];
 419     const ssize_t len = UnixDomainSocket::RecvMsg(
 420         kZygoteSocketPairFd, buf, sizeof(buf), &recv_fds);
 421     CHECK_GT(len, 0);
 422     CHECK(recv_fds.empty());
 423
 424     Pickle pickle(buf, len);
 425     PickleIterator iter(pickle);
 426
 427     int kind;
 428     CHECK(iter.ReadInt(&kind));
 429     CHECK(kind == kZygoteCommandForkRealPID);
 430     CHECK(iter.ReadInt(&real_pid));
 431   }
 432
 433   // Fork failed.
 434   if (pid < 0) {
 435     return -1;
 436   }
 437
 438   // If we successfully forked a child, but it crashed without sending
 439   // a message to the browser, the browser won't have found its PID.
 440   if (real_pid < 0) {
 441     KillAndReap(pid, helper);
 442     return -1;
 443   }
 444
 445   // If we're not using a helper, send the PID back to the child process.
 446   if (!helper) {
 447     ssize_t written =
 448         HANDLE_EINTR(write(write_pipe.get(), &real_pid, sizeof(real_pid)));
 449     if (written != sizeof(real_pid)) {
 450       KillAndReap(pid, helper);
 451       return -1;
 452     }
 453   }
 454
 455   // Now set-up this process to be tracked by the Zygote.
 456   if (process_info_map_.find(real_pid) != process_info_map_.end()) {
 457     LOG(ERROR) << "Already tracking PID " << real_pid;
 458     NOTREACHED();
 459   }
 460   process_info_map_[real_pid].internal_pid = pid;
 461   process_info_map_[real_pid].started_from_helper = helper;
 462
 463   return real_pid;
 464 }
 465
 466 base::ProcessId Zygote::ReadArgsAndFork(PickleIterator iter,
 467                                         ScopedVector<base::ScopedFD> fds,
 468                                         std::string* uma_name,
 469                                         int* uma_sample,
 470                                         int* uma_boundary_value) {
 471   std::vector<std::string> args;
 472   int argc = 0;
 473   int numfds = 0;
 474   base::GlobalDescriptors::Mapping mapping;
 475   std::string process_type;
 476   std::string channel_id;
 477   const std::string channel_id_prefix = std::string("--")
 478       + switches::kProcessChannelID + std::string("=");
 479
 480   if (!iter.ReadString(&process_type))
 481     return -1;
 482   if (!iter.ReadInt(&argc))
 483     return -1;
 484
 485   for (int i = 0; i < argc; ++i) {
 486     std::string arg;
 487     if (!iter.ReadString(&arg))
 488       return -1;
 489     args.push_back(arg);
 490     if (arg.compare(0, channel_id_prefix.length(), channel_id_prefix) == 0)
 491       channel_id = arg.substr(channel_id_prefix.length());
 492   }
 493
 494   if (!iter.ReadInt(&numfds))
 495     return -1;
 496   if (numfds != static_cast<int>(fds.size()))
 497     return -1;
 498
 499   // First FD is the PID oracle socket.
 500   if (fds.size() < 1)
 501     return -1;
 502   base::ScopedFD pid_oracle(fds[0]->Pass());
 503
 504   // Remaining FDs are for the global descriptor mapping.
 505   for (int i = 1; i < numfds; ++i) {
 506     base::GlobalDescriptors::Key key;
 507     if (!iter.ReadUInt32(&key))
 508       return -1;
 509     mapping.push_back(base::GlobalDescriptors::Descriptor(key, fds[i]->get()));
 510   }
 511
 512   mapping.push_back(base::GlobalDescriptors::Descriptor(
 513       static_cast<uint32_t>(kSandboxIPCChannel), GetSandboxFD()));
 514
 515   // Returns twice, once per process.
 516   base::ProcessId child_pid = ForkWithRealPid(process_type,
 517                                               mapping,
 518                                               channel_id,
 519                                               pid_oracle.Pass(),
 520                                               uma_name,
 521                                               uma_sample,
 522                                               uma_boundary_value);
 523   if (!child_pid) {
 524     // This is the child process.
 525
 526     // Our socket from the browser.
 527     PCHECK(0 == IGNORE_EINTR(close(kZygoteSocketPairFd)));
 528
 529     // Pass ownership of file descriptors from fds to GlobalDescriptors.
 530     for (ScopedVector<base::ScopedFD>::iterator i = fds.begin(); i != fds.end();
 531          ++i)
 532       ignore_result((*i)->release());
 533     base::GlobalDescriptors::GetInstance()->Reset(mapping);
 534
 535     // Reset the process-wide command line to our new command line.
 536     base::CommandLine::Reset();
 537     base::CommandLine::Init(0, NULL);
 538     base::CommandLine::ForCurrentProcess()->InitFromArgv(args);
 539
 540     // Update the process title. The argv was already cached by the call to
 541     // SetProcessTitleFromCommandLine in ChromeMain, so we can pass NULL here
 542     // (we don't have the original argv at this point).
 543     SetProcessTitleFromCommandLine(NULL);
 544   } else if (child_pid < 0) {
 545     LOG(ERROR) << "Zygote could not fork: process_type " << process_type
 546         << " numfds " << numfds << " child_pid " << child_pid;
 547   }
 548   return child_pid;
 549 }
 550
 551 bool Zygote::HandleForkRequest(int fd,
 552                                PickleIterator iter,
 553                                ScopedVector<base::ScopedFD> fds) {
 554   std::string uma_name;
 555   int uma_sample;
 556   int uma_boundary_value;
 557   base::ProcessId child_pid = ReadArgsAndFork(
 558       iter, fds.Pass(), &uma_name, &uma_sample, &uma_boundary_value);
 559   if (child_pid == 0)
 560     return true;
 561   // If there's no UMA report for this particular fork, then check if any
 562   // helpers have an initial UMA report for us to send instead.
 563   while (uma_name.empty() && initial_uma_index_ < helpers_.size()) {
 564     helpers_[initial_uma_index_++]->InitialUMA(
 565         &uma_name, &uma_sample, &uma_boundary_value);
 566   }
 567   // Must always send reply, as ZygoteHost blocks while waiting for it.
 568   Pickle reply_pickle;
 569   reply_pickle.WriteInt(child_pid);
 570   reply_pickle.WriteString(uma_name);
 571   if (!uma_name.empty()) {
 572     reply_pickle.WriteInt(uma_sample);
 573     reply_pickle.WriteInt(uma_boundary_value);
 574   }
 575   if (HANDLE_EINTR(write(fd, reply_pickle.data(), reply_pickle.size())) !=
 576       static_cast<ssize_t> (reply_pickle.size()))
 577     PLOG(ERROR) << "write";
 578   return false;
 579 }
 580
 581 bool Zygote::HandleGetSandboxStatus(int fd,
 582                                     PickleIterator iter) {
 583   if (HANDLE_EINTR(write(fd, &sandbox_flags_, sizeof(sandbox_flags_))) !=
 584                    sizeof(sandbox_flags_)) {
 585     PLOG(ERROR) << "write";
 586   }
 587
 588   return false;
 589 }
 590
 591 }  // namespace content