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/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/zygote_fork_delegate_linux.h"
  33 #include "ipc/ipc_channel.h"
  34 #include "ipc/ipc_switches.h"
  35
  36 #if defined(ADDRESS_SANITIZER)
  37 #include <sanitizer/asan_interface.h>
  38 #endif
  39
  40 // See http://code.google.com/p/chromium/wiki/LinuxZygote
  41
  42 namespace content {
  43
  44 namespace {
  45
  46 // NOP function. See below where this handler is installed.
  47 void SIGCHLDHandler(int signal) {
  48 }
  49
  50 int LookUpFd(const base::GlobalDescriptors::Mapping& fd_mapping, uint32_t key) {
  51   for (size_t index = 0; index < fd_mapping.size(); ++index) {
  52     if (fd_mapping[index].first == key)
  53       return fd_mapping[index].second;
  54   }
  55   return -1;
  56 }
  57
  58 void CreatePipe(base::ScopedFD* read_pipe, base::ScopedFD* write_pipe) {
  59   int raw_pipe[2];
  60   PCHECK(0 == pipe(raw_pipe));
  61   read_pipe->reset(raw_pipe[0]);
  62   write_pipe->reset(raw_pipe[1]);
  63 }
  64
  65 void KillAndReap(pid_t pid, ZygoteForkDelegate* helper) {
  66   if (helper) {
  67     // Helper children may be forked in another PID namespace, so |pid| might
  68     // be meaningless to us; or we just might not be able to directly send it
  69     // signals.  So we can't kill it.
  70     // Additionally, we're not its parent, so we can't reap it anyway.
  71     // TODO(mdempsky): Extend the ZygoteForkDelegate API to handle this.
  72     LOG(WARNING) << "Unable to kill or reap helper children";
  73     return;
  74   }
  75
  76   // Kill the child process in case it's not already dead, so we can safely
  77   // perform a blocking wait.
  78   PCHECK(0 == kill(pid, SIGKILL));
  79   PCHECK(pid == HANDLE_EINTR(waitpid(pid, NULL, 0)));
  80 }
  81
  82 }  // namespace
  83
  84 Zygote::Zygote(int sandbox_flags, ScopedVector<ZygoteForkDelegate> helpers,
  85                const std::vector<base::ProcessHandle>& extra_children,
  86                const std::vector<int>& extra_fds)
  87     : sandbox_flags_(sandbox_flags),
  88       helpers_(helpers.Pass()),
  89       initial_uma_index_(0),
  90       extra_children_(extra_children),
  91       extra_fds_(extra_fds) {}
  92
  93 Zygote::~Zygote() {
  94 }
  95
  96 bool Zygote::ProcessRequests() {
  97   // A SOCK_SEQPACKET socket is installed in fd 3. We get commands from the
  98   // browser on it.
  99   // A SOCK_DGRAM is installed in fd 5. This is the sandbox IPC channel.
 100   // See http://code.google.com/p/chromium/wiki/LinuxSandboxIPC
 101
 102   // We need to accept SIGCHLD, even though our handler is a no-op because
 103   // otherwise we cannot wait on children. (According to POSIX 2001.)
 104   struct sigaction action;
 105   memset(&action, 0, sizeof(action));
 106   action.sa_handler = &SIGCHLDHandler;
 107   CHECK(sigaction(SIGCHLD, &action, NULL) == 0);
 108
 109   if (UsingSUIDSandbox()) {
 110     // Let the ZygoteHost know we are ready to go.
 111     // The receiving code is in content/browser/zygote_host_linux.cc.
 112     bool r = UnixDomainSocket::SendMsg(kZygoteSocketPairFd,
 113                                        kZygoteHelloMessage,
 114                                        sizeof(kZygoteHelloMessage),
 115                                        std::vector<int>());
 116 #if defined(OS_CHROMEOS)
 117     LOG_IF(WARNING, !r) << "Sending zygote magic failed";
 118     // Exit normally on chromeos because session manager may send SIGTERM
 119     // right after the process starts and it may fail to send zygote magic
 120     // number to browser process.
 121     if (!r)
 122       _exit(RESULT_CODE_NORMAL_EXIT);
 123 #else
 124     CHECK(r) << "Sending zygote magic failed";
 125 #endif
 126   }
 127
 128   for (;;) {
 129     // This function call can return multiple times, once per fork().
 130     if (HandleRequestFromBrowser(kZygoteSocketPairFd))
 131       return true;
 132   }
 133 }
 134
 135 bool Zygote::GetProcessInfo(base::ProcessHandle pid,
 136                             ZygoteProcessInfo* process_info) {
 137   DCHECK(process_info);
 138   const ZygoteProcessMap::const_iterator it = process_info_map_.find(pid);
 139   if (it == process_info_map_.end()) {
 140     return false;
 141   }
 142   *process_info = it->second;
 143   return true;
 144 }
 145
 146 bool Zygote::UsingSUIDSandbox() const {
 147   return sandbox_flags_ & kSandboxLinuxSUID;
 148 }
 149
 150 bool Zygote::HandleRequestFromBrowser(int fd) {
 151   ScopedVector<base::ScopedFD> fds;
 152   char buf[kZygoteMaxMessageLength];
 153   const ssize_t len = UnixDomainSocket::RecvMsg(fd, buf, sizeof(buf), &fds);
 154
 155   if (len == 0 || (len == -1 && errno == ECONNRESET)) {
 156     // EOF from the browser. We should die.
 157     // TODO(earthdok): call __sanititizer_cov_dump() here to obtain code
 158     // coverage  for the Zygote. Currently it's not possible because of
 159     // confusion over who is responsible for closing the file descriptor.
 160     for (std::vector<int>::iterator it = extra_fds_.begin();
 161          it < extra_fds_.end(); ++it) {
 162       PCHECK(0 == IGNORE_EINTR(close(*it)));
 163     }
 164 #if !defined(ADDRESS_SANITIZER)
 165     // TODO(earthdok): add watchdog thread before using this in non-ASAN builds.
 166     CHECK(extra_children_.empty());
 167 #endif
 168     for (std::vector<base::ProcessHandle>::iterator it =
 169              extra_children_.begin();
 170          it < extra_children_.end(); ++it) {
 171       PCHECK(*it == HANDLE_EINTR(waitpid(*it, NULL, 0)));
 172     }
 173     _exit(0);
 174     return false;
 175   }
 176
 177   if (len == -1) {
 178     PLOG(ERROR) << "Error reading message from browser";
 179     return false;
 180   }
 181
 182   Pickle pickle(buf, len);
 183   PickleIterator iter(pickle);
 184
 185   int kind;
 186   if (pickle.ReadInt(&iter, &kind)) {
 187     switch (kind) {
 188       case kZygoteCommandFork:
 189         // This function call can return multiple times, once per fork().
 190         return HandleForkRequest(fd, pickle, iter, fds.Pass());
 191
 192       case kZygoteCommandReap:
 193         if (!fds.empty())
 194           break;
 195         HandleReapRequest(fd, pickle, iter);
 196         return false;
 197       case kZygoteCommandGetTerminationStatus:
 198         if (!fds.empty())
 199           break;
 200         HandleGetTerminationStatus(fd, pickle, iter);
 201         return false;
 202       case kZygoteCommandGetSandboxStatus:
 203         HandleGetSandboxStatus(fd, pickle, iter);
 204         return false;
 205       case kZygoteCommandForkRealPID:
 206         // This shouldn't happen in practice, but some failure paths in
 207         // HandleForkRequest (e.g., if ReadArgsAndFork fails during depickling)
 208         // could leave this command pending on the socket.
 209         LOG(ERROR) << "Unexpected real PID message from browser";
 210         NOTREACHED();
 211         return false;
 212       default:
 213         NOTREACHED();
 214         break;
 215     }
 216   }
 217
 218   LOG(WARNING) << "Error parsing message from browser";
 219   return false;
 220 }
 221
 222 // TODO(jln): remove callers to this broken API. See crbug.com/274855.
 223 void Zygote::HandleReapRequest(int fd,
 224                                const Pickle& pickle,
 225                                PickleIterator iter) {
 226   base::ProcessId child;
 227
 228   if (!pickle.ReadInt(&iter, &child)) {
 229     LOG(WARNING) << "Error parsing reap request from browser";
 230     return;
 231   }
 232
 233   ZygoteProcessInfo child_info;
 234   if (!GetProcessInfo(child, &child_info)) {
 235     LOG(ERROR) << "Child not found!";
 236     NOTREACHED();
 237     return;
 238   }
 239
 240   if (!child_info.started_from_helper) {
 241     // Do not call base::EnsureProcessTerminated() under ThreadSanitizer, as it
 242     // spawns a separate thread which may live until the call to fork() in the
 243     // zygote. As a result, ThreadSanitizer will report an error and almost
 244     // disable race detection in the child process.
 245     // Not calling EnsureProcessTerminated() may result in zombie processes
 246     // sticking around. This will only happen during testing, so we can live
 247     // with this for now.
 248 #if !defined(THREAD_SANITIZER)
 249     // TODO(jln): this old code is completely broken. See crbug.com/274855.
 250     base::EnsureProcessTerminated(child_info.internal_pid);
 251 #else
 252     LOG(WARNING) << "Zygote process omitting a call to "
 253         << "base::EnsureProcessTerminated() for child pid " << child
 254         << " under ThreadSanitizer. See http://crbug.com/274855.";
 255 #endif
 256   } else {
 257     // For processes from the helper, send a GetTerminationStatus request
 258     // with known_dead set to true.
 259     // This is not perfect, as the process may be killed instantly, but is
 260     // better than ignoring the request.
 261     base::TerminationStatus status;
 262     int exit_code;
 263     bool got_termination_status =
 264         GetTerminationStatus(child, true /* known_dead */, &status, &exit_code);
 265     DCHECK(got_termination_status);
 266   }
 267   process_info_map_.erase(child);
 268 }
 269
 270 bool Zygote::GetTerminationStatus(base::ProcessHandle real_pid,
 271                                   bool known_dead,
 272                                   base::TerminationStatus* status,
 273                                   int* exit_code) {
 274
 275   ZygoteProcessInfo child_info;
 276   if (!GetProcessInfo(real_pid, &child_info)) {
 277     LOG(ERROR) << "Zygote::GetTerminationStatus for unknown PID "
 278                << real_pid;
 279     NOTREACHED();
 280     return false;
 281   }
 282   // We know about |real_pid|.
 283   const base::ProcessHandle child = child_info.internal_pid;
 284   if (child_info.started_from_helper) {
 285     if (!child_info.started_from_helper->GetTerminationStatus(
 286             child, known_dead, status, exit_code)) {
 287       return false;
 288     }
 289   } else {
 290     // Handle the request directly.
 291     if (known_dead) {
 292       *status = base::GetKnownDeadTerminationStatus(child, exit_code);
 293     } else {
 294       // We don't know if the process is dying, so get its status but don't
 295       // wait.
 296       *status = base::GetTerminationStatus(child, exit_code);
 297     }
 298   }
 299   // Successfully got a status for |real_pid|.
 300   if (*status != base::TERMINATION_STATUS_STILL_RUNNING) {
 301     // Time to forget about this process.
 302     process_info_map_.erase(real_pid);
 303   }
 304   return true;
 305 }
 306
 307 void Zygote::HandleGetTerminationStatus(int fd,
 308                                         const Pickle& pickle,
 309                                         PickleIterator iter) {
 310   bool known_dead;
 311   base::ProcessHandle child_requested;
 312
 313   if (!pickle.ReadBool(&iter, &known_dead) ||
 314       !pickle.ReadInt(&iter, &child_requested)) {
 315     LOG(WARNING) << "Error parsing GetTerminationStatus request "
 316                  << "from browser";
 317     return;
 318   }
 319
 320   base::TerminationStatus status;
 321   int exit_code;
 322
 323   bool got_termination_status =
 324       GetTerminationStatus(child_requested, known_dead, &status, &exit_code);
 325   if (!got_termination_status) {
 326     // Assume that if we can't find the child in the sandbox, then
 327     // it terminated normally.
 328     NOTREACHED();
 329     status = base::TERMINATION_STATUS_NORMAL_TERMINATION;
 330     exit_code = RESULT_CODE_NORMAL_EXIT;
 331   }
 332
 333   Pickle write_pickle;
 334   write_pickle.WriteInt(static_cast<int>(status));
 335   write_pickle.WriteInt(exit_code);
 336   ssize_t written =
 337       HANDLE_EINTR(write(fd, write_pickle.data(), write_pickle.size()));
 338   if (written != static_cast<ssize_t>(write_pickle.size()))
 339     PLOG(ERROR) << "write";
 340 }
 341
 342 int Zygote::ForkWithRealPid(const std::string& process_type,
 343                             const base::GlobalDescriptors::Mapping& fd_mapping,
 344                             const std::string& channel_id,
 345                             base::ScopedFD pid_oracle,
 346                             std::string* uma_name,
 347                             int* uma_sample,
 348                             int* uma_boundary_value) {
 349   ZygoteForkDelegate* helper = NULL;
 350   for (ScopedVector<ZygoteForkDelegate>::iterator i = helpers_.begin();
 351        i != helpers_.end();
 352        ++i) {
 353     if ((*i)->CanHelp(process_type, uma_name, uma_sample, uma_boundary_value)) {
 354       helper = *i;
 355       break;
 356     }
 357   }
 358
 359   base::ScopedFD read_pipe, write_pipe;
 360   base::ProcessId pid = 0;
 361   if (helper) {
 362     int ipc_channel_fd = LookUpFd(fd_mapping, kPrimaryIPCChannel);
 363     if (ipc_channel_fd < 0) {
 364       DLOG(ERROR) << "Failed to find kPrimaryIPCChannel in FD mapping";
 365       return -1;
 366     }
 367     std::vector<int> fds;
 368     fds.push_back(ipc_channel_fd);  // kBrowserFDIndex
 369     fds.push_back(pid_oracle.get());  // kPIDOracleFDIndex
 370     pid = helper->Fork(process_type, fds, channel_id);
 371
 372     // Helpers should never return in the child process.
 373     CHECK_NE(pid, 0);
 374   } else {
 375     CreatePipe(&read_pipe, &write_pipe);
 376     pid = fork();
 377   }
 378
 379   if (pid == 0) {
 380     // In the child process.
 381     write_pipe.reset();
 382
 383     // Ping the PID oracle socket so the browser can find our PID.
 384     CHECK(SendZygoteChildPing(pid_oracle.get()));
 385
 386     // Now read back our real PID from the zygote.
 387     base::ProcessId real_pid;
 388     if (!base::ReadFromFD(read_pipe.get(),
 389                           reinterpret_cast<char*>(&real_pid),
 390                           sizeof(real_pid))) {
 391       LOG(FATAL) << "Failed to synchronise with parent zygote process";
 392     }
 393     if (real_pid <= 0) {
 394       LOG(FATAL) << "Invalid pid from parent zygote";
 395     }
 396 #if defined(OS_LINUX)
 397     // Sandboxed processes need to send the global, non-namespaced PID when
 398     // setting up an IPC channel to their parent.
 399     IPC::Channel::SetGlobalPid(real_pid);
 400     // Force the real PID so chrome event data have a PID that corresponds
 401     // to system trace event data.
 402     base::debug::TraceLog::GetInstance()->SetProcessID(
 403         static_cast<int>(real_pid));
 404 #endif
 405     return 0;
 406   }
 407
 408   // In the parent process.
 409   read_pipe.reset();
 410   pid_oracle.reset();
 411
 412   // Always receive a real PID from the zygote host, though it might
 413   // be invalid (see below).
 414   base::ProcessId real_pid;
 415   {
 416     ScopedVector<base::ScopedFD> recv_fds;
 417     char buf[kZygoteMaxMessageLength];
 418     const ssize_t len = UnixDomainSocket::RecvMsg(
 419         kZygoteSocketPairFd, buf, sizeof(buf), &recv_fds);
 420     CHECK_GT(len, 0);
 421     CHECK(recv_fds.empty());
 422
 423     Pickle pickle(buf, len);
 424     PickleIterator iter(pickle);
 425
 426     int kind;
 427     CHECK(pickle.ReadInt(&iter, &kind));
 428     CHECK(kind == kZygoteCommandForkRealPID);
 429     CHECK(pickle.ReadInt(&iter, &real_pid));
 430   }
 431
 432   // Fork failed.
 433   if (pid < 0) {
 434     return -1;
 435   }
 436
 437   // If we successfully forked a child, but it crashed without sending
 438   // a message to the browser, the browser won't have found its PID.
 439   if (real_pid < 0) {
 440     KillAndReap(pid, helper);
 441     return -1;
 442   }
 443
 444   // If we're not using a helper, send the PID back to the child process.
 445   if (!helper) {
 446     ssize_t written =
 447         HANDLE_EINTR(write(write_pipe.get(), &real_pid, sizeof(real_pid)));
 448     if (written != sizeof(real_pid)) {
 449       KillAndReap(pid, helper);
 450       return -1;
 451     }
 452   }
 453
 454   // Now set-up this process to be tracked by the Zygote.
 455   if (process_info_map_.find(real_pid) != process_info_map_.end()) {
 456     LOG(ERROR) << "Already tracking PID " << real_pid;
 457     NOTREACHED();
 458   }
 459   process_info_map_[real_pid].internal_pid = pid;
 460   process_info_map_[real_pid].started_from_helper = helper;
 461
 462   return real_pid;
 463 }
 464
 465 base::ProcessId Zygote::ReadArgsAndFork(const Pickle& pickle,
 466                                         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 (!pickle.ReadString(&iter, &process_type))
 481     return -1;
 482   if (!pickle.ReadInt(&iter, &argc))
 483     return -1;
 484
 485   for (int i = 0; i < argc; ++i) {
 486     std::string arg;
 487     if (!pickle.ReadString(&iter, &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 (!pickle.ReadInt(&iter, &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 (!pickle.ReadUInt32(&iter, &key))
 508       return -1;
 509     mapping.push_back(std::make_pair(key, fds[i]->get()));
 510   }
 511
 512   mapping.push_back(std::make_pair(
 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     CommandLine::Reset();
 537     CommandLine::Init(0, NULL);
 538     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                                const Pickle& pickle,
 553                                PickleIterator iter,
 554                                ScopedVector<base::ScopedFD> fds) {
 555   std::string uma_name;
 556   int uma_sample;
 557   int uma_boundary_value;
 558   base::ProcessId child_pid = ReadArgsAndFork(
 559       pickle, iter, fds.Pass(), &uma_name, &uma_sample, &uma_boundary_value);
 560   if (child_pid == 0)
 561     return true;
 562   // If there's no UMA report for this particular fork, then check if any
 563   // helpers have an initial UMA report for us to send instead.
 564   while (uma_name.empty() && initial_uma_index_ < helpers_.size()) {
 565     helpers_[initial_uma_index_++]->InitialUMA(
 566         &uma_name, &uma_sample, &uma_boundary_value);
 567   }
 568   // Must always send reply, as ZygoteHost blocks while waiting for it.
 569   Pickle reply_pickle;
 570   reply_pickle.WriteInt(child_pid);
 571   reply_pickle.WriteString(uma_name);
 572   if (!uma_name.empty()) {
 573     reply_pickle.WriteInt(uma_sample);
 574     reply_pickle.WriteInt(uma_boundary_value);
 575   }
 576   if (HANDLE_EINTR(write(fd, reply_pickle.data(), reply_pickle.size())) !=
 577       static_cast<ssize_t> (reply_pickle.size()))
 578     PLOG(ERROR) << "write";
 579   return false;
 580 }
 581
 582 bool Zygote::HandleGetSandboxStatus(int fd,
 583                                     const Pickle& pickle,
 584                                     PickleIterator iter) {
 585   if (HANDLE_EINTR(write(fd, &sandbox_flags_, sizeof(sandbox_flags_))) !=
 586                    sizeof(sandbox_flags_)) {
 587     PLOG(ERROR) << "write";
 588   }
 589
 590   return false;
 591 }
 592
 593 }  // namespace content