content/zygote/zygote_main_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_main.h"
   6
   7 #include <dlfcn.h>
   8 #include <fcntl.h>
   9 #include <pthread.h>
  10 #include <signal.h>
  11 #include <string.h>
  12 #include <sys/socket.h>
  13 #include <sys/types.h>
  14 #include <unistd.h>
  15
  16 #include <vector>
  17
  18 #include "base/basictypes.h"
  19 #include "base/bind.h"
  20 #include "base/command_line.h"
  21 #include "base/compiler_specific.h"
  22 #include "base/memory/scoped_vector.h"
  23 #include "base/native_library.h"
  24 #include "base/pickle.h"
  25 #include "base/posix/eintr_wrapper.h"
  26 #include "base/posix/unix_domain_socket_linux.h"
  27 #include "base/rand_util.h"
  28 #include "base/strings/safe_sprintf.h"
  29 #include "base/strings/string_number_conversions.h"
  30 #include "base/sys_info.h"
  31 #include "build/build_config.h"
  32 #include "content/common/child_process_sandbox_support_impl_linux.h"
  33 #include "content/common/font_config_ipc_linux.h"
  34 #include "content/common/sandbox_linux/sandbox_debug_handling_linux.h"
  35 #include "content/common/sandbox_linux/sandbox_linux.h"
  36 #include "content/common/zygote_commands_linux.h"
  37 #include "content/public/common/content_switches.h"
  38 #include "content/public/common/main_function_params.h"
  39 #include "content/public/common/sandbox_linux.h"
  40 #include "content/public/common/zygote_fork_delegate_linux.h"
  41 #include "content/zygote/zygote_linux.h"
  42 #include "crypto/nss_util.h"
  43 #include "sandbox/linux/services/credentials.h"
  44 #include "sandbox/linux/services/init_process_reaper.h"
  45 #include "sandbox/linux/services/namespace_sandbox.h"
  46 #include "sandbox/linux/services/thread_helpers.h"
  47 #include "sandbox/linux/suid/client/setuid_sandbox_client.h"
  48 #include "third_party/icu/source/i18n/unicode/timezone.h"
  49 #include "third_party/skia/include/ports/SkFontConfigInterface.h"
  50
  51 #if defined(OS_LINUX)
  52 #include <sys/prctl.h>
  53 #endif
  54
  55 #if defined(USE_OPENSSL)
  56 #include <openssl/rand.h>
  57 #else
  58 #include "sandbox/linux/services/libc_urandom_override.h"
  59 #endif
  60
  61 #if defined(ENABLE_PLUGINS)
  62 #include "content/common/pepper_plugin_list.h"
  63 #include "content/public/common/pepper_plugin_info.h"
  64 #endif
  65
  66 #if defined(ENABLE_WEBRTC)
  67 #include "third_party/libjingle/overrides/init_webrtc.h"
  68 #endif
  69
  70 #if defined(SANITIZER_COVERAGE)
  71 #include <sanitizer/common_interface_defs.h>
  72 #include <sanitizer/coverage_interface.h>
  73 #endif
  74
  75 namespace content {
  76
  77 namespace {
  78
  79 void CloseFds(const std::vector<int>& fds) {
  80   for (const auto& it : fds) {
  81     PCHECK(0 == IGNORE_EINTR(close(it)));
  82   }
  83 }
  84
  85 void RunTwoClosures(const base::Closure* first, const base::Closure* second) {
  86   first->Run();
  87   second->Run();
  88 }
  89
  90 }  // namespace
  91
  92 // See http://code.google.com/p/chromium/wiki/LinuxZygote
  93
  94 static void ProxyLocaltimeCallToBrowser(time_t input, struct tm* output,
  95                                         char* timezone_out,
  96                                         size_t timezone_out_len) {
  97   base::Pickle request;
  98   request.WriteInt(LinuxSandbox::METHOD_LOCALTIME);
  99   request.WriteString(
 100       std::string(reinterpret_cast<char*>(&input), sizeof(input)));
 101
 102   uint8_t reply_buf[512];
 103   const ssize_t r = base::UnixDomainSocket::SendRecvMsg(
 104       GetSandboxFD(), reply_buf, sizeof(reply_buf), NULL, request);
 105   if (r == -1) {
 106     memset(output, 0, sizeof(struct tm));
 107     return;
 108   }
 109
 110   base::Pickle reply(reinterpret_cast<char*>(reply_buf), r);
 111   base::PickleIterator iter(reply);
 112   std::string result, timezone;
 113   if (!iter.ReadString(&result) ||
 114       !iter.ReadString(&timezone) ||
 115       result.size() != sizeof(struct tm)) {
 116     memset(output, 0, sizeof(struct tm));
 117     return;
 118   }
 119
 120   memcpy(output, result.data(), sizeof(struct tm));
 121   if (timezone_out_len) {
 122     const size_t copy_len = std::min(timezone_out_len - 1, timezone.size());
 123     memcpy(timezone_out, timezone.data(), copy_len);
 124     timezone_out[copy_len] = 0;
 125     output->tm_zone = timezone_out;
 126   } else {
 127     output->tm_zone = NULL;
 128   }
 129 }
 130
 131 static bool g_am_zygote_or_renderer = false;
 132
 133 // Sandbox interception of libc calls.
 134 //
 135 // Because we are running in a sandbox certain libc calls will fail (localtime
 136 // being the motivating example - it needs to read /etc/localtime). We need to
 137 // intercept these calls and proxy them to the browser. However, these calls
 138 // may come from us or from our libraries. In some cases we can't just change
 139 // our code.
 140 //
 141 // It's for these cases that we have the following setup:
 142 //
 143 // We define global functions for those functions which we wish to override.
 144 // Since we will be first in the dynamic resolution order, the dynamic linker
 145 // will point callers to our versions of these functions. However, we have the
 146 // same binary for both the browser and the renderers, which means that our
 147 // overrides will apply in the browser too.
 148 //
 149 // The global |g_am_zygote_or_renderer| is true iff we are in a zygote or
 150 // renderer process. It's set in ZygoteMain and inherited by the renderers when
 151 // they fork. (This means that it'll be incorrect for global constructor
 152 // functions and before ZygoteMain is called - beware).
 153 //
 154 // Our replacement functions can check this global and either proxy
 155 // the call to the browser over the sandbox IPC
 156 // (http://code.google.com/p/chromium/wiki/LinuxSandboxIPC) or they can use
 157 // dlsym with RTLD_NEXT to resolve the symbol, ignoring any symbols in the
 158 // current module.
 159 //
 160 // Other avenues:
 161 //
 162 // Our first attempt involved some assembly to patch the GOT of the current
 163 // module. This worked, but was platform specific and doesn't catch the case
 164 // where a library makes a call rather than current module.
 165 //
 166 // We also considered patching the function in place, but this would again by
 167 // platform specific and the above technique seems to work well enough.
 168
 169 typedef struct tm* (*LocaltimeFunction)(const time_t* timep);
 170 typedef struct tm* (*LocaltimeRFunction)(const time_t* timep,
 171                                          struct tm* result);
 172
 173 static pthread_once_t g_libc_localtime_funcs_guard = PTHREAD_ONCE_INIT;
 174 static LocaltimeFunction g_libc_localtime;
 175 static LocaltimeFunction g_libc_localtime64;
 176 static LocaltimeRFunction g_libc_localtime_r;
 177 static LocaltimeRFunction g_libc_localtime64_r;
 178
 179 static void InitLibcLocaltimeFunctions() {
 180   g_libc_localtime = reinterpret_cast<LocaltimeFunction>(
 181       dlsym(RTLD_NEXT, "localtime"));
 182   g_libc_localtime64 = reinterpret_cast<LocaltimeFunction>(
 183       dlsym(RTLD_NEXT, "localtime64"));
 184   g_libc_localtime_r = reinterpret_cast<LocaltimeRFunction>(
 185       dlsym(RTLD_NEXT, "localtime_r"));
 186   g_libc_localtime64_r = reinterpret_cast<LocaltimeRFunction>(
 187       dlsym(RTLD_NEXT, "localtime64_r"));
 188
 189   if (!g_libc_localtime || !g_libc_localtime_r) {
 190     // http://code.google.com/p/chromium/issues/detail?id=16800
 191     //
 192     // Nvidia's libGL.so overrides dlsym for an unknown reason and replaces
 193     // it with a version which doesn't work. In this case we'll get a NULL
 194     // result. There's not a lot we can do at this point, so we just bodge it!
 195     LOG(ERROR) << "Your system is broken: dlsym doesn't work! This has been "
 196                   "reported to be caused by Nvidia's libGL. You should expect"
 197                   " time related functions to misbehave. "
 198                   "http://code.google.com/p/chromium/issues/detail?id=16800";
 199   }
 200
 201   if (!g_libc_localtime)
 202     g_libc_localtime = gmtime;
 203   if (!g_libc_localtime64)
 204     g_libc_localtime64 = g_libc_localtime;
 205   if (!g_libc_localtime_r)
 206     g_libc_localtime_r = gmtime_r;
 207   if (!g_libc_localtime64_r)
 208     g_libc_localtime64_r = g_libc_localtime_r;
 209 }
 210
 211 // Define localtime_override() function with asm name "localtime", so that all
 212 // references to localtime() will resolve to this function. Notice that we need
 213 // to set visibility attribute to "default" to export the symbol, as it is set
 214 // to "hidden" by default in chrome per build/common.gypi.
 215 __attribute__ ((__visibility__("default")))
 216 struct tm* localtime_override(const time_t* timep) __asm__ ("localtime");
 217
 218 __attribute__ ((__visibility__("default")))
 219 struct tm* localtime_override(const time_t* timep) {
 220   if (g_am_zygote_or_renderer) {
 221     static struct tm time_struct;
 222     static char timezone_string[64];
 223     ProxyLocaltimeCallToBrowser(*timep, &time_struct, timezone_string,
 224                                 sizeof(timezone_string));
 225     return &time_struct;
 226   } else {
 227     CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
 228                              InitLibcLocaltimeFunctions));
 229     struct tm* res = g_libc_localtime(timep);
 230 #if defined(MEMORY_SANITIZER)
 231     if (res) __msan_unpoison(res, sizeof(*res));
 232     if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
 233 #endif
 234     return res;
 235   }
 236 }
 237
 238 // Use same trick to override localtime64(), localtime_r() and localtime64_r().
 239 __attribute__ ((__visibility__("default")))
 240 struct tm* localtime64_override(const time_t* timep) __asm__ ("localtime64");
 241
 242 __attribute__ ((__visibility__("default")))
 243 struct tm* localtime64_override(const time_t* timep) {
 244   if (g_am_zygote_or_renderer) {
 245     static struct tm time_struct;
 246     static char timezone_string[64];
 247     ProxyLocaltimeCallToBrowser(*timep, &time_struct, timezone_string,
 248                                 sizeof(timezone_string));
 249     return &time_struct;
 250   } else {
 251     CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
 252                              InitLibcLocaltimeFunctions));
 253     struct tm* res = g_libc_localtime64(timep);
 254 #if defined(MEMORY_SANITIZER)
 255     if (res) __msan_unpoison(res, sizeof(*res));
 256     if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
 257 #endif
 258     return res;
 259   }
 260 }
 261
 262 __attribute__ ((__visibility__("default")))
 263 struct tm* localtime_r_override(const time_t* timep,
 264                                 struct tm* result) __asm__ ("localtime_r");
 265
 266 __attribute__ ((__visibility__("default")))
 267 struct tm* localtime_r_override(const time_t* timep, struct tm* result) {
 268   if (g_am_zygote_or_renderer) {
 269     ProxyLocaltimeCallToBrowser(*timep, result, NULL, 0);
 270     return result;
 271   } else {
 272     CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
 273                              InitLibcLocaltimeFunctions));
 274     struct tm* res = g_libc_localtime_r(timep, result);
 275 #if defined(MEMORY_SANITIZER)
 276     if (res) __msan_unpoison(res, sizeof(*res));
 277     if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
 278 #endif
 279     return res;
 280   }
 281 }
 282
 283 __attribute__ ((__visibility__("default")))
 284 struct tm* localtime64_r_override(const time_t* timep,
 285                                   struct tm* result) __asm__ ("localtime64_r");
 286
 287 __attribute__ ((__visibility__("default")))
 288 struct tm* localtime64_r_override(const time_t* timep, struct tm* result) {
 289   if (g_am_zygote_or_renderer) {
 290     ProxyLocaltimeCallToBrowser(*timep, result, NULL, 0);
 291     return result;
 292   } else {
 293     CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
 294                              InitLibcLocaltimeFunctions));
 295     struct tm* res = g_libc_localtime64_r(timep, result);
 296 #if defined(MEMORY_SANITIZER)
 297     if (res) __msan_unpoison(res, sizeof(*res));
 298     if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
 299 #endif
 300     return res;
 301   }
 302 }
 303
 304 #if defined(ENABLE_PLUGINS)
 305 // Loads the (native) libraries but does not initialize them (i.e., does not
 306 // call PPP_InitializeModule). This is needed by the zygote on Linux to get
 307 // access to the plugins before entering the sandbox.
 308 void PreloadPepperPlugins() {
 309   std::vector<PepperPluginInfo> plugins;
 310   ComputePepperPluginList(&plugins);
 311   for (size_t i = 0; i < plugins.size(); ++i) {
 312     if (!plugins[i].is_internal) {
 313       base::NativeLibraryLoadError error;
 314       base::NativeLibrary library = base::LoadNativeLibrary(plugins[i].path,
 315                                                             &error);
 316       VLOG_IF(1, !library) << "Unable to load plugin "
 317                            << plugins[i].path.value() << " "
 318                            << error.ToString();
 319
 320       (void)library;  // Prevent release-mode warning.
 321     }
 322   }
 323 }
 324 #endif
 325
 326 // This function triggers the static and lazy construction of objects that need
 327 // to be created before imposing the sandbox.
 328 static void ZygotePreSandboxInit() {
 329   base::RandUint64();
 330
 331   base::SysInfo::AmountOfPhysicalMemory();
 332   base::SysInfo::MaxSharedMemorySize();
 333   base::SysInfo::NumberOfProcessors();
 334
 335   // ICU DateFormat class (used in base/time_format.cc) needs to get the
 336   // Olson timezone ID by accessing the zoneinfo files on disk. After
 337   // TimeZone::createDefault is called once here, the timezone ID is
 338   // cached and there's no more need to access the file system.
 339   scoped_ptr<icu::TimeZone> zone(icu::TimeZone::createDefault());
 340
 341 #if defined(USE_OPENSSL)
 342   // Pass BoringSSL a copy of the /dev/urandom file descriptor so RAND_bytes
 343   // will work inside the sandbox.
 344   RAND_set_urandom_fd(base::GetUrandomFD());
 345 #else
 346   // NSS libraries are loaded before sandbox is activated. This is to allow
 347   // successful initialization of NSS which tries to load extra library files.
 348   crypto::LoadNSSLibraries();
 349 #endif
 350 #if defined(ENABLE_PLUGINS)
 351   // Ensure access to the Pepper plugins before the sandbox is turned on.
 352   PreloadPepperPlugins();
 353 #endif
 354 #if defined(ENABLE_WEBRTC)
 355   InitializeWebRtcModule();
 356 #endif
 357   SkFontConfigInterface::SetGlobal(
 358       new FontConfigIPC(GetSandboxFD()))->unref();
 359 }
 360
 361 static bool CreateInitProcessReaper(base::Closure* post_fork_parent_callback) {
 362   // The current process becomes init(1), this function returns from a
 363   // newly created process.
 364   const bool init_created =
 365       sandbox::CreateInitProcessReaper(post_fork_parent_callback);
 366   if (!init_created) {
 367     LOG(ERROR) << "Error creating an init process to reap zombies";
 368     return false;
 369   }
 370   return true;
 371 }
 372
 373 // Enter the setuid sandbox. This requires the current process to have been
 374 // created through the setuid sandbox.
 375 static bool EnterSuidSandbox(sandbox::SetuidSandboxClient* setuid_sandbox,
 376                              base::Closure* post_fork_parent_callback) {
 377   DCHECK(setuid_sandbox);
 378   DCHECK(setuid_sandbox->IsSuidSandboxChild());
 379
 380   // Use the SUID sandbox.  This still allows the seccomp sandbox to
 381   // be enabled by the process later.
 382
 383   if (!setuid_sandbox->IsSuidSandboxUpToDate()) {
 384     LOG(WARNING) <<
 385         "You are using a wrong version of the setuid binary!\n"
 386         "Please read "
 387         "https://code.google.com/p/chromium/wiki/LinuxSUIDSandboxDevelopment."
 388         "\n\n";
 389   }
 390
 391   if (!setuid_sandbox->ChrootMe())
 392     return false;
 393
 394   if (setuid_sandbox->IsInNewPIDNamespace()) {
 395     CHECK_EQ(1, getpid())
 396         << "The SUID sandbox created a new PID namespace but Zygote "
 397            "is not the init process. Please, make sure the SUID "
 398            "binary is up to date.";
 399   }
 400
 401   if (getpid() == 1) {
 402     // The setuid sandbox has created a new PID namespace and we need
 403     // to assume the role of init.
 404     CHECK(CreateInitProcessReaper(post_fork_parent_callback));
 405   }
 406
 407   CHECK(SandboxDebugHandling::SetDumpableStatusAndHandlers());
 408   return true;
 409 }
 410
 411 static void DropAllCapabilities(int proc_fd) {
 412   CHECK(sandbox::Credentials::DropAllCapabilities(proc_fd));
 413 }
 414
 415 static void EnterNamespaceSandbox(LinuxSandbox* linux_sandbox,
 416                                   base::Closure* post_fork_parent_callback) {
 417   linux_sandbox->EngageNamespaceSandbox();
 418
 419   if (getpid() == 1) {
 420     base::Closure drop_all_caps_callback =
 421         base::Bind(&DropAllCapabilities, linux_sandbox->proc_fd());
 422     base::Closure callback = base::Bind(
 423         &RunTwoClosures, &drop_all_caps_callback, post_fork_parent_callback);
 424     CHECK(CreateInitProcessReaper(&callback));
 425   }
 426 }
 427
 428 #if defined(SANITIZER_COVERAGE)
 429 static int g_sanitizer_message_length = 1 * 1024 * 1024;
 430
 431 // A helper process which collects code coverage data from the renderers over a
 432 // socket and dumps it to a file. See http://crbug.com/336212 for discussion.
 433 static void SanitizerCoverageHelper(int socket_fd, int file_fd) {
 434   scoped_ptr<char[]> buffer(new char[g_sanitizer_message_length]);
 435   while (true) {
 436     ssize_t received_size = HANDLE_EINTR(
 437         recv(socket_fd, buffer.get(), g_sanitizer_message_length, 0));
 438     PCHECK(received_size >= 0);
 439     if (received_size == 0)
 440       // All clients have closed the socket. We should die.
 441       _exit(0);
 442     PCHECK(file_fd >= 0);
 443     ssize_t written_size = 0;
 444     while (written_size < received_size) {
 445       ssize_t write_res =
 446           HANDLE_EINTR(write(file_fd, buffer.get() + written_size,
 447                              received_size - written_size));
 448       PCHECK(write_res >= 0);
 449       written_size += write_res;
 450     }
 451     PCHECK(0 == HANDLE_EINTR(fsync(file_fd)));
 452   }
 453 }
 454
 455 // fds[0] is the read end, fds[1] is the write end.
 456 static void CreateSanitizerCoverageSocketPair(int fds[2]) {
 457   PCHECK(0 == socketpair(AF_UNIX, SOCK_SEQPACKET, 0, fds));
 458   PCHECK(0 == shutdown(fds[0], SHUT_WR));
 459   PCHECK(0 == shutdown(fds[1], SHUT_RD));
 460
 461   // Find the right buffer size for sending coverage data.
 462   // The kernel will silently set the buffer size to the allowed maximum when
 463   // the specified size is too large, so we set our desired size and read it
 464   // back.
 465   int* buf_size = &g_sanitizer_message_length;
 466   socklen_t option_length = sizeof(*buf_size);
 467   PCHECK(0 == setsockopt(fds[1], SOL_SOCKET, SO_SNDBUF,
 468                          buf_size, option_length));
 469   PCHECK(0 == getsockopt(fds[1], SOL_SOCKET, SO_SNDBUF,
 470                          buf_size, &option_length));
 471   DCHECK_EQ(sizeof(*buf_size), option_length);
 472   // The kernel returns the doubled buffer size.
 473   *buf_size /= 2;
 474   PCHECK(*buf_size > 0);
 475 }
 476
 477 static pid_t ForkSanitizerCoverageHelper(
 478     int child_fd,
 479     int parent_fd,
 480     base::ScopedFD file_fd,
 481     const std::vector<int>& extra_fds_to_close) {
 482   pid_t pid = fork();
 483   PCHECK(pid >= 0);
 484   if (pid == 0) {
 485     // In the child.
 486     PCHECK(0 == IGNORE_EINTR(close(parent_fd)));
 487     CloseFds(extra_fds_to_close);
 488     SanitizerCoverageHelper(child_fd, file_fd.get());
 489     _exit(0);
 490   } else {
 491     // In the parent.
 492     PCHECK(0 == IGNORE_EINTR(close(child_fd)));
 493     return pid;
 494   }
 495 }
 496
 497 #endif  // defined(SANITIZER_COVERAGE)
 498
 499 static void EnterLayerOneSandbox(LinuxSandbox* linux_sandbox,
 500                                  const bool using_layer1_sandbox,
 501                                  base::Closure* post_fork_parent_callback) {
 502   DCHECK(linux_sandbox);
 503
 504   ZygotePreSandboxInit();
 505
 506   // Check that the pre-sandbox initialization didn't spawn threads.
 507 #if !defined(THREAD_SANITIZER)
 508   DCHECK(sandbox::ThreadHelpers::IsSingleThreaded());
 509 #endif
 510
 511   sandbox::SetuidSandboxClient* setuid_sandbox =
 512       linux_sandbox->setuid_sandbox_client();
 513   if (setuid_sandbox->IsSuidSandboxChild()) {
 514     CHECK(EnterSuidSandbox(setuid_sandbox, post_fork_parent_callback))
 515         << "Failed to enter setuid sandbox";
 516   } else if (sandbox::NamespaceSandbox::InNewUserNamespace()) {
 517     EnterNamespaceSandbox(linux_sandbox, post_fork_parent_callback);
 518   } else {
 519     CHECK(!using_layer1_sandbox);
 520   }
 521 }
 522
 523 bool ZygoteMain(const MainFunctionParams& params,
 524                 ScopedVector<ZygoteForkDelegate> fork_delegates) {
 525   g_am_zygote_or_renderer = true;
 526 #if !defined(USE_OPENSSL)
 527   sandbox::InitLibcUrandomOverrides();
 528 #endif
 529
 530   std::vector<int> fds_to_close_post_fork;
 531
 532   LinuxSandbox* linux_sandbox = LinuxSandbox::GetInstance();
 533
 534 #if defined(SANITIZER_COVERAGE)
 535   const std::string sancov_file_name =
 536       "zygote." + base::Uint64ToString(base::RandUint64());
 537   base::ScopedFD sancov_file_fd(
 538       __sanitizer_maybe_open_cov_file(sancov_file_name.c_str()));
 539   int sancov_socket_fds[2] = {-1, -1};
 540   CreateSanitizerCoverageSocketPair(sancov_socket_fds);
 541   linux_sandbox->sanitizer_args()->coverage_sandboxed = 1;
 542   linux_sandbox->sanitizer_args()->coverage_fd = sancov_socket_fds[1];
 543   linux_sandbox->sanitizer_args()->coverage_max_block_size =
 544       g_sanitizer_message_length;
 545   // Zygote termination will block until the helper process exits, which will
 546   // not happen until the write end of the socket is closed everywhere. Make
 547   // sure the init process does not hold on to it.
 548   fds_to_close_post_fork.push_back(sancov_socket_fds[0]);
 549   fds_to_close_post_fork.push_back(sancov_socket_fds[1]);
 550 #endif  // SANITIZER_COVERAGE
 551
 552   // Skip pre-initializing sandbox under --no-sandbox for crbug.com/444900.
 553   if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
 554           switches::kNoSandbox)) {
 555     // This will pre-initialize the various sandboxes that need it.
 556     linux_sandbox->PreinitializeSandbox();
 557   }
 558
 559   const bool using_setuid_sandbox =
 560       linux_sandbox->setuid_sandbox_client()->IsSuidSandboxChild();
 561   const bool using_namespace_sandbox =
 562       sandbox::NamespaceSandbox::InNewUserNamespace();
 563   const bool using_layer1_sandbox =
 564       using_setuid_sandbox || using_namespace_sandbox;
 565
 566   if (using_setuid_sandbox) {
 567     linux_sandbox->setuid_sandbox_client()->CloseDummyFile();
 568   }
 569
 570   if (using_layer1_sandbox) {
 571     // Let the ZygoteHost know we're booting up.
 572     CHECK(base::UnixDomainSocket::SendMsg(kZygoteSocketPairFd,
 573                                           kZygoteBootMessage,
 574                                           sizeof(kZygoteBootMessage),
 575                                           std::vector<int>()));
 576   }
 577
 578   VLOG(1) << "ZygoteMain: initializing " << fork_delegates.size()
 579           << " fork delegates";
 580   for (ZygoteForkDelegate* fork_delegate : fork_delegates) {
 581     fork_delegate->Init(GetSandboxFD(), using_layer1_sandbox);
 582   }
 583
 584   const std::vector<int> sandbox_fds_to_close_post_fork =
 585       linux_sandbox->GetFileDescriptorsToClose();
 586
 587   fds_to_close_post_fork.insert(fds_to_close_post_fork.end(),
 588                                 sandbox_fds_to_close_post_fork.begin(),
 589                                 sandbox_fds_to_close_post_fork.end());
 590   base::Closure post_fork_parent_callback =
 591       base::Bind(&CloseFds, fds_to_close_post_fork);
 592
 593   // Turn on the first layer of the sandbox if the configuration warrants it.
 594   EnterLayerOneSandbox(linux_sandbox, using_layer1_sandbox,
 595                        &post_fork_parent_callback);
 596
 597   // Extra children and file descriptors created that the Zygote must have
 598   // knowledge of.
 599   std::vector<pid_t> extra_children;
 600   std::vector<int> extra_fds;
 601
 602 #if defined(SANITIZER_COVERAGE)
 603   pid_t sancov_helper_pid = ForkSanitizerCoverageHelper(
 604       sancov_socket_fds[0], sancov_socket_fds[1], sancov_file_fd.Pass(),
 605       sandbox_fds_to_close_post_fork);
 606   // It's important that the zygote reaps the helper before dying. Otherwise,
 607   // the destruction of the PID namespace could kill the helper before it
 608   // completes its I/O tasks. |sancov_helper_pid| will exit once the last
 609   // renderer holding the write end of |sancov_socket_fds| closes it.
 610   extra_children.push_back(sancov_helper_pid);
 611   // Sanitizer code in the renderers will inherit the write end of the socket
 612   // from the zygote. We must keep it open until the very end of the zygote's
 613   // lifetime, even though we don't explicitly use it.
 614   extra_fds.push_back(sancov_socket_fds[1]);
 615 #endif  // SANITIZER_COVERAGE
 616
 617   const int sandbox_flags = linux_sandbox->GetStatus();
 618
 619   const bool setuid_sandbox_engaged = sandbox_flags & kSandboxLinuxSUID;
 620   CHECK_EQ(using_setuid_sandbox, setuid_sandbox_engaged);
 621
 622   const bool namespace_sandbox_engaged = sandbox_flags & kSandboxLinuxUserNS;
 623   CHECK_EQ(using_namespace_sandbox, namespace_sandbox_engaged);
 624
 625   Zygote zygote(sandbox_flags, fork_delegates.Pass(), extra_children,
 626                 extra_fds);
 627   // This function call can return multiple times, once per fork().
 628   return zygote.ProcessRequests();
 629 }
 630
 631 }  // namespace content