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/files/file_util.h"
  15 #include "base/linux_util.h"
  16 #include "base/logging.h"
  17 #include "base/macros.h"
  18 #include "base/memory/scoped_vector.h"
  19 #include "base/pickle.h"
  20 #include "base/posix/eintr_wrapper.h"
  21 #include "base/posix/global_descriptors.h"
  22 #include "base/posix/unix_domain_socket_linux.h"
  23 #include "base/process/kill.h"
  24 #include "base/process/launch.h"
  25 #include "base/process/process.h"
  26 #include "base/process/process_handle.h"
  27 #include "base/trace_event/trace_event.h"
  28 #include "content/common/child_process_sandbox_support_impl_linux.h"
  29 #include "content/common/sandbox_linux/sandbox_linux.h"
  30 #include "content/common/set_process_title.h"
  31 #include "content/common/zygote_commands_linux.h"
  32 #include "content/public/common/content_descriptors.h"
  33 #include "content/public/common/result_codes.h"
  34 #include "content/public/common/sandbox_linux.h"
  35 #include "content/public/common/send_zygote_child_ping_linux.h"
  36 #include "content/public/common/zygote_fork_delegate_linux.h"
  37 #include "ipc/ipc_channel.h"
  38 #include "ipc/ipc_switches.h"
  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].key == key)
  53       return fd_mapping[index].fd;
  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() || UsingNSSandbox()) {
 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::UsingNSSandbox() const {
 151   return sandbox_flags_ & kSandboxLinuxUserNS;
 152 }
 153
 154 bool Zygote::HandleRequestFromBrowser(int fd) {
 155   ScopedVector<base::ScopedFD> fds;
 156   char buf[kZygoteMaxMessageLength];
 157   const ssize_t len = UnixDomainSocket::RecvMsg(fd, buf, sizeof(buf), &fds);
 158
 159   if (len == 0 || (len == -1 && errno == ECONNRESET)) {
 160     // EOF from the browser. We should die.
 161     // TODO(earthdok): call __sanititizer_cov_dump() here to obtain code
 162     // coverage  for the Zygote. Currently it's not possible because of
 163     // confusion over who is responsible for closing the file descriptor.
 164     for (std::vector<int>::iterator it = extra_fds_.begin();
 165          it < extra_fds_.end(); ++it) {
 166       PCHECK(0 == IGNORE_EINTR(close(*it)));
 167     }
 168 #if !defined(SANITIZER_COVERAGE)
 169     // TODO(earthdok): add watchdog thread before using this in builds not
 170     // using sanitizer coverage.
 171     CHECK(extra_children_.empty());
 172 #endif
 173     for (std::vector<base::ProcessHandle>::iterator it =
 174              extra_children_.begin();
 175          it < extra_children_.end(); ++it) {
 176       PCHECK(*it == HANDLE_EINTR(waitpid(*it, NULL, 0)));
 177     }
 178     _exit(0);
 179     return false;
 180   }
 181
 182   if (len == -1) {
 183     PLOG(ERROR) << "Error reading message from browser";
 184     return false;
 185   }
 186
 187   Pickle pickle(buf, len);
 188   PickleIterator iter(pickle);
 189
 190   int kind;
 191   if (iter.ReadInt(&kind)) {
 192     switch (kind) {
 193       case kZygoteCommandFork:
 194         // This function call can return multiple times, once per fork().
 195         return HandleForkRequest(fd, iter, fds.Pass());
 196
 197       case kZygoteCommandReap:
 198         if (!fds.empty())
 199           break;
 200         HandleReapRequest(fd, iter);
 201         return false;
 202       case kZygoteCommandGetTerminationStatus:
 203         if (!fds.empty())
 204           break;
 205         HandleGetTerminationStatus(fd, iter);
 206         return false;
 207       case kZygoteCommandGetSandboxStatus:
 208         HandleGetSandboxStatus(fd, iter);
 209         return false;
 210       case kZygoteCommandForkRealPID:
 211         // This shouldn't happen in practice, but some failure paths in
 212         // HandleForkRequest (e.g., if ReadArgsAndFork fails during depickling)
 213         // could leave this command pending on the socket.
 214         LOG(ERROR) << "Unexpected real PID message from browser";
 215         NOTREACHED();
 216         return false;
 217       default:
 218         NOTREACHED();
 219         break;
 220     }
 221   }
 222
 223   LOG(WARNING) << "Error parsing message from browser";
 224   return false;
 225 }
 226
 227 // TODO(jln): remove callers to this broken API. See crbug.com/274855.
 228 void Zygote::HandleReapRequest(int fd,
 229                                PickleIterator iter) {
 230   base::ProcessId child;
 231
 232   if (!iter.ReadInt(&child)) {
 233     LOG(WARNING) << "Error parsing reap request from browser";
 234     return;
 235   }
 236
 237   ZygoteProcessInfo child_info;
 238   if (!GetProcessInfo(child, &child_info)) {
 239     LOG(ERROR) << "Child not found!";
 240     NOTREACHED();
 241     return;
 242   }
 243
 244   if (!child_info.started_from_helper) {
 245     // Do not call base::EnsureProcessTerminated() under ThreadSanitizer, as it
 246     // spawns a separate thread which may live until the call to fork() in the
 247     // zygote. As a result, ThreadSanitizer will report an error and almost
 248     // disable race detection in the child process.
 249     // Not calling EnsureProcessTerminated() may result in zombie processes
 250     // sticking around. This will only happen during testing, so we can live
 251     // with this for now.
 252 #if !defined(THREAD_SANITIZER)
 253     // TODO(jln): this old code is completely broken. See crbug.com/274855.
 254     base::EnsureProcessTerminated(base::Process(child_info.internal_pid));
 255 #else
 256     LOG(WARNING) << "Zygote process omitting a call to "
 257         << "base::EnsureProcessTerminated() for child pid " << child
 258         << " under ThreadSanitizer. See http://crbug.com/274855.";
 259 #endif
 260   } else {
 261     // For processes from the helper, send a GetTerminationStatus request
 262     // with known_dead set to true.
 263     // This is not perfect, as the process may be killed instantly, but is
 264     // better than ignoring the request.
 265     base::TerminationStatus status;
 266     int exit_code;
 267     bool got_termination_status =
 268         GetTerminationStatus(child, true /* known_dead */, &status, &exit_code);
 269     DCHECK(got_termination_status);
 270   }
 271   process_info_map_.erase(child);
 272 }
 273
 274 bool Zygote::GetTerminationStatus(base::ProcessHandle real_pid,
 275                                   bool known_dead,
 276                                   base::TerminationStatus* status,
 277                                   int* exit_code) {
 278
 279   ZygoteProcessInfo child_info;
 280   if (!GetProcessInfo(real_pid, &child_info)) {
 281     LOG(ERROR) << "Zygote::GetTerminationStatus for unknown PID "
 282                << real_pid;
 283     NOTREACHED();
 284     return false;
 285   }
 286   // We know about |real_pid|.
 287   const base::ProcessHandle child = child_info.internal_pid;
 288   if (child_info.started_from_helper) {
 289     if (!child_info.started_from_helper->GetTerminationStatus(
 290             child, known_dead, status, exit_code)) {
 291       return false;
 292     }
 293   } else {
 294     // Handle the request directly.
 295     if (known_dead) {
 296       *status = base::GetKnownDeadTerminationStatus(child, exit_code);
 297     } else {
 298       // We don't know if the process is dying, so get its status but don't
 299       // wait.
 300       *status = base::GetTerminationStatus(child, exit_code);
 301     }
 302   }
 303   // Successfully got a status for |real_pid|.
 304   if (*status != base::TERMINATION_STATUS_STILL_RUNNING) {
 305     // Time to forget about this process.
 306     process_info_map_.erase(real_pid);
 307   }
 308   return true;
 309 }
 310
 311 void Zygote::HandleGetTerminationStatus(int fd,
 312                                         PickleIterator iter) {
 313   bool known_dead;
 314   base::ProcessHandle child_requested;
 315
 316   if (!iter.ReadBool(&known_dead) || !iter.ReadInt(&child_requested)) {
 317     LOG(WARNING) << "Error parsing GetTerminationStatus request "
 318                  << "from browser";
 319     return;
 320   }
 321
 322   base::TerminationStatus status;
 323   int exit_code;
 324
 325   bool got_termination_status =
 326       GetTerminationStatus(child_requested, known_dead, &status, &exit_code);
 327   if (!got_termination_status) {
 328     // Assume that if we can't find the child in the sandbox, then
 329     // it terminated normally.
 330     NOTREACHED();
 331     status = base::TERMINATION_STATUS_NORMAL_TERMINATION;
 332     exit_code = RESULT_CODE_NORMAL_EXIT;
 333   }
 334
 335   Pickle write_pickle;
 336   write_pickle.WriteInt(static_cast<int>(status));
 337   write_pickle.WriteInt(exit_code);
 338   ssize_t written =
 339       HANDLE_EINTR(write(fd, write_pickle.data(), write_pickle.size()));
 340   if (written != static_cast<ssize_t>(write_pickle.size()))
 341     PLOG(ERROR) << "write";
 342 }
 343
 344 int Zygote::ForkWithRealPid(const std::string& process_type,
 345                             const base::GlobalDescriptors::Mapping& fd_mapping,
 346                             const std::string& channel_id,
 347                             base::ScopedFD pid_oracle,
 348                             std::string* uma_name,
 349                             int* uma_sample,
 350                             int* uma_boundary_value) {
 351   ZygoteForkDelegate* helper = NULL;
 352   for (ScopedVector<ZygoteForkDelegate>::iterator i = helpers_.begin();
 353        i != helpers_.end();
 354        ++i) {
 355     if ((*i)->CanHelp(process_type, uma_name, uma_sample, uma_boundary_value)) {
 356       helper = *i;
 357       break;
 358     }
 359   }
 360
 361   base::ScopedFD read_pipe, write_pipe;
 362   base::ProcessId pid = 0;
 363   if (helper) {
 364     int ipc_channel_fd = LookUpFd(fd_mapping, kPrimaryIPCChannel);
 365     if (ipc_channel_fd < 0) {
 366       DLOG(ERROR) << "Failed to find kPrimaryIPCChannel in FD mapping";
 367       return -1;
 368     }
 369     std::vector<int> fds;
 370     fds.push_back(ipc_channel_fd);  // kBrowserFDIndex
 371     fds.push_back(pid_oracle.get());  // kPIDOracleFDIndex
 372     pid = helper->Fork(process_type, fds, channel_id);
 373
 374     // Helpers should never return in the child process.
 375     CHECK_NE(pid, 0);
 376   } else {
 377     CreatePipe(&read_pipe, &write_pipe);
 378     // This is roughly equivalent to a fork(). We are using ForkWithFlags mainly
 379     // to give it some more diverse test coverage.
 380     pid = base::ForkWithFlags(SIGCHLD, nullptr, nullptr);
 381   }
 382
 383   if (pid == 0) {
 384     // In the child process.
 385     write_pipe.reset();
 386
 387     // Ping the PID oracle socket so the browser can find our PID.
 388     CHECK(SendZygoteChildPing(pid_oracle.get()));
 389
 390     // Now read back our real PID from the zygote.
 391     base::ProcessId real_pid;
 392     if (!base::ReadFromFD(read_pipe.get(),
 393                           reinterpret_cast<char*>(&real_pid),
 394                           sizeof(real_pid))) {
 395       LOG(FATAL) << "Failed to synchronise with parent zygote process";
 396     }
 397     if (real_pid <= 0) {
 398       LOG(FATAL) << "Invalid pid from parent zygote";
 399     }
 400 #if defined(OS_LINUX)
 401     // Sandboxed processes need to send the global, non-namespaced PID when
 402     // setting up an IPC channel to their parent.
 403     IPC::Channel::SetGlobalPid(real_pid);
 404     // Force the real PID so chrome event data have a PID that corresponds
 405     // to system trace event data.
 406     base::trace_event::TraceLog::GetInstance()->SetProcessID(
 407         static_cast<int>(real_pid));
 408 #endif
 409     return 0;
 410   }
 411
 412   // In the parent process.
 413   read_pipe.reset();
 414   pid_oracle.reset();
 415
 416   // Always receive a real PID from the zygote host, though it might
 417   // be invalid (see below).
 418   base::ProcessId real_pid;
 419   {
 420     ScopedVector<base::ScopedFD> recv_fds;
 421     char buf[kZygoteMaxMessageLength];
 422     const ssize_t len = UnixDomainSocket::RecvMsg(
 423         kZygoteSocketPairFd, buf, sizeof(buf), &recv_fds);
 424     CHECK_GT(len, 0);
 425     CHECK(recv_fds.empty());
 426
 427     Pickle pickle(buf, len);
 428     PickleIterator iter(pickle);
 429
 430     int kind;
 431     CHECK(iter.ReadInt(&kind));
 432     CHECK(kind == kZygoteCommandForkRealPID);
 433     CHECK(iter.ReadInt(&real_pid));
 434   }
 435
 436   // Fork failed.
 437   if (pid < 0) {
 438     return -1;
 439   }
 440
 441   // If we successfully forked a child, but it crashed without sending
 442   // a message to the browser, the browser won't have found its PID.
 443   if (real_pid < 0) {
 444     KillAndReap(pid, helper);
 445     return -1;
 446   }
 447
 448   // If we're not using a helper, send the PID back to the child process.
 449   if (!helper) {
 450     ssize_t written =
 451         HANDLE_EINTR(write(write_pipe.get(), &real_pid, sizeof(real_pid)));
 452     if (written != sizeof(real_pid)) {
 453       KillAndReap(pid, helper);
 454       return -1;
 455     }
 456   }
 457
 458   // Now set-up this process to be tracked by the Zygote.
 459   if (process_info_map_.find(real_pid) != process_info_map_.end()) {
 460     LOG(ERROR) << "Already tracking PID " << real_pid;
 461     NOTREACHED();
 462   }
 463   process_info_map_[real_pid].internal_pid = pid;
 464   process_info_map_[real_pid].started_from_helper = helper;
 465
 466   return real_pid;
 467 }
 468
 469 base::ProcessId Zygote::ReadArgsAndFork(PickleIterator iter,
 470                                         ScopedVector<base::ScopedFD> fds,
 471                                         std::string* uma_name,
 472                                         int* uma_sample,
 473                                         int* uma_boundary_value) {
 474   std::vector<std::string> args;
 475   int argc = 0;
 476   int numfds = 0;
 477   base::GlobalDescriptors::Mapping mapping;
 478   std::string process_type;
 479   std::string channel_id;
 480   const std::string channel_id_prefix = std::string("--")
 481       + switches::kProcessChannelID + std::string("=");
 482
 483   if (!iter.ReadString(&process_type))
 484     return -1;
 485   if (!iter.ReadInt(&argc))
 486     return -1;
 487
 488   for (int i = 0; i < argc; ++i) {
 489     std::string arg;
 490     if (!iter.ReadString(&arg))
 491       return -1;
 492     args.push_back(arg);
 493     if (arg.compare(0, channel_id_prefix.length(), channel_id_prefix) == 0)
 494       channel_id = arg.substr(channel_id_prefix.length());
 495   }
 496
 497   if (!iter.ReadInt(&numfds))
 498     return -1;
 499   if (numfds != static_cast<int>(fds.size()))
 500     return -1;
 501
 502   // First FD is the PID oracle socket.
 503   if (fds.size() < 1)
 504     return -1;
 505   base::ScopedFD pid_oracle(fds[0]->Pass());
 506
 507   // Remaining FDs are for the global descriptor mapping.
 508   for (int i = 1; i < numfds; ++i) {
 509     base::GlobalDescriptors::Key key;
 510     if (!iter.ReadUInt32(&key))
 511       return -1;
 512     mapping.push_back(base::GlobalDescriptors::Descriptor(key, fds[i]->get()));
 513   }
 514
 515   mapping.push_back(base::GlobalDescriptors::Descriptor(
 516       static_cast<uint32_t>(kSandboxIPCChannel), GetSandboxFD()));
 517
 518   // Returns twice, once per process.
 519   base::ProcessId child_pid = ForkWithRealPid(process_type,
 520                                               mapping,
 521                                               channel_id,
 522                                               pid_oracle.Pass(),
 523                                               uma_name,
 524                                               uma_sample,
 525                                               uma_boundary_value);
 526   if (!child_pid) {
 527     // This is the child process.
 528
 529     // Our socket from the browser.
 530     PCHECK(0 == IGNORE_EINTR(close(kZygoteSocketPairFd)));
 531
 532     // Pass ownership of file descriptors from fds to GlobalDescriptors.
 533     for (ScopedVector<base::ScopedFD>::iterator i = fds.begin(); i != fds.end();
 534          ++i)
 535       ignore_result((*i)->release());
 536     base::GlobalDescriptors::GetInstance()->Reset(mapping);
 537
 538     // Reset the process-wide command line to our new command line.
 539     base::CommandLine::Reset();
 540     base::CommandLine::Init(0, NULL);
 541     base::CommandLine::ForCurrentProcess()->InitFromArgv(args);
 542
 543     // Update the process title. The argv was already cached by the call to
 544     // SetProcessTitleFromCommandLine in ChromeMain, so we can pass NULL here
 545     // (we don't have the original argv at this point).
 546     SetProcessTitleFromCommandLine(NULL);
 547   } else if (child_pid < 0) {
 548     LOG(ERROR) << "Zygote could not fork: process_type " << process_type
 549         << " numfds " << numfds << " child_pid " << child_pid;
 550   }
 551   return child_pid;
 552 }
 553
 554 bool Zygote::HandleForkRequest(int fd,
 555                                PickleIterator iter,
 556                                ScopedVector<base::ScopedFD> fds) {
 557   std::string uma_name;
 558   int uma_sample;
 559   int uma_boundary_value;
 560   base::ProcessId child_pid = ReadArgsAndFork(
 561       iter, fds.Pass(), &uma_name, &uma_sample, &uma_boundary_value);
 562   if (child_pid == 0)
 563     return true;
 564   // If there's no UMA report for this particular fork, then check if any
 565   // helpers have an initial UMA report for us to send instead.
 566   while (uma_name.empty() && initial_uma_index_ < helpers_.size()) {
 567     helpers_[initial_uma_index_++]->InitialUMA(
 568         &uma_name, &uma_sample, &uma_boundary_value);
 569   }
 570   // Must always send reply, as ZygoteHost blocks while waiting for it.
 571   Pickle reply_pickle;
 572   reply_pickle.WriteInt(child_pid);
 573   reply_pickle.WriteString(uma_name);
 574   if (!uma_name.empty()) {
 575     reply_pickle.WriteInt(uma_sample);
 576     reply_pickle.WriteInt(uma_boundary_value);
 577   }
 578   if (HANDLE_EINTR(write(fd, reply_pickle.data(), reply_pickle.size())) !=
 579       static_cast<ssize_t> (reply_pickle.size()))
 580     PLOG(ERROR) << "write";
 581   return false;
 582 }
 583
 584 bool Zygote::HandleGetSandboxStatus(int fd,
 585                                     PickleIterator iter) {
 586   if (HANDLE_EINTR(write(fd, &sandbox_flags_, sizeof(sandbox_flags_))) !=
 587                    sizeof(sandbox_flags_)) {
 588     PLOG(ERROR) << "write";
 589   }
 590
 591   return false;
 592 }
 593
 594 }  // namespace content