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 <errno.h>
   9 #include <fcntl.h>
  10 #include <pthread.h>
  11 #include <stdio.h>
  12 #include <sys/socket.h>
  13 #include <sys/stat.h>
  14 #include <sys/types.h>
  15 #include <sys/wait.h>
  16 #include <unistd.h>
  17
  18 #include "base/basictypes.h"
  19 #include "base/bind.h"
  20 #include "base/callback.h"
  21 #include "base/command_line.h"
  22 #include "base/compiler_specific.h"
  23 #include "base/linux_util.h"
  24 #include "base/memory/scoped_vector.h"
  25 #include "base/native_library.h"
  26 #include "base/pickle.h"
  27 #include "base/posix/eintr_wrapper.h"
  28 #include "base/posix/unix_domain_socket_linux.h"
  29 #include "base/rand_util.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/pepper_plugin_list.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/pepper_plugin_info.h"
  40 #include "content/public/common/sandbox_linux.h"
  41 #include "content/public/common/zygote_fork_delegate_linux.h"
  42 #include "content/zygote/zygote_linux.h"
  43 #include "crypto/nss_util.h"
  44 #include "sandbox/linux/services/init_process_reaper.h"
  45 #include "sandbox/linux/services/libc_urandom_override.h"
  46 #include "sandbox/linux/suid/client/setuid_sandbox_client.h"
  47 #include "third_party/icu/source/i18n/unicode/timezone.h"
  48 #include "third_party/skia/include/ports/SkFontConfigInterface.h"
  49
  50 #if defined(OS_LINUX)
  51 #include <sys/epoll.h>
  52 #include <sys/prctl.h>
  53 #include <sys/signal.h>
  54 #else
  55 #include <signal.h>
  56 #endif
  57
  58 #if defined(ENABLE_WEBRTC)
  59 #include "third_party/libjingle/overrides/init_webrtc.h"
  60 #endif
  61
  62 namespace content {
  63
  64 // See http://code.google.com/p/chromium/wiki/LinuxZygote
  65
  66 static void ProxyLocaltimeCallToBrowser(time_t input, struct tm* output,
  67                                         char* timezone_out,
  68                                         size_t timezone_out_len) {
  69   Pickle request;
  70   request.WriteInt(LinuxSandbox::METHOD_LOCALTIME);
  71   request.WriteString(
  72       std::string(reinterpret_cast<char*>(&input), sizeof(input)));
  73
  74   uint8_t reply_buf[512];
  75   const ssize_t r = UnixDomainSocket::SendRecvMsg(
  76       GetSandboxFD(), reply_buf, sizeof(reply_buf), NULL,
  77       request);
  78   if (r == -1) {
  79     memset(output, 0, sizeof(struct tm));
  80     return;
  81   }
  82
  83   Pickle reply(reinterpret_cast<char*>(reply_buf), r);
  84   PickleIterator iter(reply);
  85   std::string result, timezone;
  86   if (!reply.ReadString(&iter, &result) ||
  87       !reply.ReadString(&iter, &timezone) ||
  88       result.size() != sizeof(struct tm)) {
  89     memset(output, 0, sizeof(struct tm));
  90     return;
  91   }
  92
  93   memcpy(output, result.data(), sizeof(struct tm));
  94   if (timezone_out_len) {
  95     const size_t copy_len = std::min(timezone_out_len - 1, timezone.size());
  96     memcpy(timezone_out, timezone.data(), copy_len);
  97     timezone_out[copy_len] = 0;
  98     output->tm_zone = timezone_out;
  99   } else {
 100     output->tm_zone = NULL;
 101   }
 102 }
 103
 104 static bool g_am_zygote_or_renderer = false;
 105
 106 // Sandbox interception of libc calls.
 107 //
 108 // Because we are running in a sandbox certain libc calls will fail (localtime
 109 // being the motivating example - it needs to read /etc/localtime). We need to
 110 // intercept these calls and proxy them to the browser. However, these calls
 111 // may come from us or from our libraries. In some cases we can't just change
 112 // our code.
 113 //
 114 // It's for these cases that we have the following setup:
 115 //
 116 // We define global functions for those functions which we wish to override.
 117 // Since we will be first in the dynamic resolution order, the dynamic linker
 118 // will point callers to our versions of these functions. However, we have the
 119 // same binary for both the browser and the renderers, which means that our
 120 // overrides will apply in the browser too.
 121 //
 122 // The global |g_am_zygote_or_renderer| is true iff we are in a zygote or
 123 // renderer process. It's set in ZygoteMain and inherited by the renderers when
 124 // they fork. (This means that it'll be incorrect for global constructor
 125 // functions and before ZygoteMain is called - beware).
 126 //
 127 // Our replacement functions can check this global and either proxy
 128 // the call to the browser over the sandbox IPC
 129 // (http://code.google.com/p/chromium/wiki/LinuxSandboxIPC) or they can use
 130 // dlsym with RTLD_NEXT to resolve the symbol, ignoring any symbols in the
 131 // current module.
 132 //
 133 // Other avenues:
 134 //
 135 // Our first attempt involved some assembly to patch the GOT of the current
 136 // module. This worked, but was platform specific and doesn't catch the case
 137 // where a library makes a call rather than current module.
 138 //
 139 // We also considered patching the function in place, but this would again by
 140 // platform specific and the above technique seems to work well enough.
 141
 142 typedef struct tm* (*LocaltimeFunction)(const time_t* timep);
 143 typedef struct tm* (*LocaltimeRFunction)(const time_t* timep,
 144                                          struct tm* result);
 145
 146 static pthread_once_t g_libc_localtime_funcs_guard = PTHREAD_ONCE_INIT;
 147 static LocaltimeFunction g_libc_localtime;
 148 static LocaltimeFunction g_libc_localtime64;
 149 static LocaltimeRFunction g_libc_localtime_r;
 150 static LocaltimeRFunction g_libc_localtime64_r;
 151
 152 static void InitLibcLocaltimeFunctions() {
 153   g_libc_localtime = reinterpret_cast<LocaltimeFunction>(
 154       dlsym(RTLD_NEXT, "localtime"));
 155   g_libc_localtime64 = reinterpret_cast<LocaltimeFunction>(
 156       dlsym(RTLD_NEXT, "localtime64"));
 157   g_libc_localtime_r = reinterpret_cast<LocaltimeRFunction>(
 158       dlsym(RTLD_NEXT, "localtime_r"));
 159   g_libc_localtime64_r = reinterpret_cast<LocaltimeRFunction>(
 160       dlsym(RTLD_NEXT, "localtime64_r"));
 161
 162   if (!g_libc_localtime || !g_libc_localtime_r) {
 163     // http://code.google.com/p/chromium/issues/detail?id=16800
 164     //
 165     // Nvidia's libGL.so overrides dlsym for an unknown reason and replaces
 166     // it with a version which doesn't work. In this case we'll get a NULL
 167     // result. There's not a lot we can do at this point, so we just bodge it!
 168     LOG(ERROR) << "Your system is broken: dlsym doesn't work! This has been "
 169                   "reported to be caused by Nvidia's libGL. You should expect"
 170                   " time related functions to misbehave. "
 171                   "http://code.google.com/p/chromium/issues/detail?id=16800";
 172   }
 173
 174   if (!g_libc_localtime)
 175     g_libc_localtime = gmtime;
 176   if (!g_libc_localtime64)
 177     g_libc_localtime64 = g_libc_localtime;
 178   if (!g_libc_localtime_r)
 179     g_libc_localtime_r = gmtime_r;
 180   if (!g_libc_localtime64_r)
 181     g_libc_localtime64_r = g_libc_localtime_r;
 182 }
 183
 184 // Define localtime_override() function with asm name "localtime", so that all
 185 // references to localtime() will resolve to this function. Notice that we need
 186 // to set visibility attribute to "default" to export the symbol, as it is set
 187 // to "hidden" by default in chrome per build/common.gypi.
 188 __attribute__ ((__visibility__("default")))
 189 struct tm* localtime_override(const time_t* timep) __asm__ ("localtime");
 190
 191 __attribute__ ((__visibility__("default")))
 192 struct tm* localtime_override(const time_t* timep) {
 193   if (g_am_zygote_or_renderer) {
 194     static struct tm time_struct;
 195     static char timezone_string[64];
 196     ProxyLocaltimeCallToBrowser(*timep, &time_struct, timezone_string,
 197                                 sizeof(timezone_string));
 198     return &time_struct;
 199   } else {
 200     CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
 201                              InitLibcLocaltimeFunctions));
 202     struct tm* res = g_libc_localtime(timep);
 203 #if defined(MEMORY_SANITIZER)
 204     if (res) __msan_unpoison(res, sizeof(*res));
 205     if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
 206 #endif
 207     return res;
 208   }
 209 }
 210
 211 // Use same trick to override localtime64(), localtime_r() and localtime64_r().
 212 __attribute__ ((__visibility__("default")))
 213 struct tm* localtime64_override(const time_t* timep) __asm__ ("localtime64");
 214
 215 __attribute__ ((__visibility__("default")))
 216 struct tm* localtime64_override(const time_t* timep) {
 217   if (g_am_zygote_or_renderer) {
 218     static struct tm time_struct;
 219     static char timezone_string[64];
 220     ProxyLocaltimeCallToBrowser(*timep, &time_struct, timezone_string,
 221                                 sizeof(timezone_string));
 222     return &time_struct;
 223   } else {
 224     CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
 225                              InitLibcLocaltimeFunctions));
 226     struct tm* res = g_libc_localtime64(timep);
 227 #if defined(MEMORY_SANITIZER)
 228     if (res) __msan_unpoison(res, sizeof(*res));
 229     if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
 230 #endif
 231     return res;
 232   }
 233 }
 234
 235 __attribute__ ((__visibility__("default")))
 236 struct tm* localtime_r_override(const time_t* timep,
 237                                 struct tm* result) __asm__ ("localtime_r");
 238
 239 __attribute__ ((__visibility__("default")))
 240 struct tm* localtime_r_override(const time_t* timep, struct tm* result) {
 241   if (g_am_zygote_or_renderer) {
 242     ProxyLocaltimeCallToBrowser(*timep, result, NULL, 0);
 243     return result;
 244   } else {
 245     CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
 246                              InitLibcLocaltimeFunctions));
 247     struct tm* res = g_libc_localtime_r(timep, result);
 248 #if defined(MEMORY_SANITIZER)
 249     if (res) __msan_unpoison(res, sizeof(*res));
 250     if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
 251 #endif
 252     return res;
 253   }
 254 }
 255
 256 __attribute__ ((__visibility__("default")))
 257 struct tm* localtime64_r_override(const time_t* timep,
 258                                   struct tm* result) __asm__ ("localtime64_r");
 259
 260 __attribute__ ((__visibility__("default")))
 261 struct tm* localtime64_r_override(const time_t* timep, struct tm* result) {
 262   if (g_am_zygote_or_renderer) {
 263     ProxyLocaltimeCallToBrowser(*timep, result, NULL, 0);
 264     return result;
 265   } else {
 266     CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
 267                              InitLibcLocaltimeFunctions));
 268     struct tm* res = g_libc_localtime64_r(timep, result);
 269 #if defined(MEMORY_SANITIZER)
 270     if (res) __msan_unpoison(res, sizeof(*res));
 271     if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
 272 #endif
 273     return res;
 274   }
 275 }
 276
 277 #if defined(ENABLE_PLUGINS)
 278 // Loads the (native) libraries but does not initialize them (i.e., does not
 279 // call PPP_InitializeModule). This is needed by the zygote on Linux to get
 280 // access to the plugins before entering the sandbox.
 281 void PreloadPepperPlugins() {
 282   std::vector<PepperPluginInfo> plugins;
 283   ComputePepperPluginList(&plugins);
 284   for (size_t i = 0; i < plugins.size(); ++i) {
 285     if (!plugins[i].is_internal && plugins[i].is_sandboxed) {
 286       base::NativeLibraryLoadError error;
 287       base::NativeLibrary library = base::LoadNativeLibrary(plugins[i].path,
 288                                                             &error);
 289       VLOG_IF(1, !library) << "Unable to load plugin "
 290                            << plugins[i].path.value() << " "
 291                            << error.ToString();
 292
 293       (void)library;  // Prevent release-mode warning.
 294     }
 295   }
 296 }
 297 #endif
 298
 299 // This function triggers the static and lazy construction of objects that need
 300 // to be created before imposing the sandbox.
 301 static void ZygotePreSandboxInit() {
 302   base::RandUint64();
 303
 304   base::SysInfo::AmountOfPhysicalMemory();
 305   base::SysInfo::MaxSharedMemorySize();
 306   base::SysInfo::NumberOfProcessors();
 307
 308   // ICU DateFormat class (used in base/time_format.cc) needs to get the
 309   // Olson timezone ID by accessing the zoneinfo files on disk. After
 310   // TimeZone::createDefault is called once here, the timezone ID is
 311   // cached and there's no more need to access the file system.
 312   scoped_ptr<icu::TimeZone> zone(icu::TimeZone::createDefault());
 313
 314 #if defined(USE_NSS)
 315   // NSS libraries are loaded before sandbox is activated. This is to allow
 316   // successful initialization of NSS which tries to load extra library files.
 317   crypto::LoadNSSLibraries();
 318 #elif defined(USE_OPENSSL)
 319   // OpenSSL is intentionally not supported in the sandboxed processes, see
 320   // http://crbug.com/99163. If that ever changes we'll likely need to init
 321   // OpenSSL here (at least, load the library and error strings).
 322 #else
 323   // It's possible that another hypothetical crypto stack would not require
 324   // pre-sandbox init, but more likely this is just a build configuration error.
 325   #error Which SSL library are you using?
 326 #endif
 327 #if defined(ENABLE_PLUGINS)
 328   // Ensure access to the Pepper plugins before the sandbox is turned on.
 329   PreloadPepperPlugins();
 330 #endif
 331 #if defined(ENABLE_WEBRTC)
 332   InitializeWebRtcModule();
 333 #endif
 334   SkFontConfigInterface::SetGlobal(
 335       new FontConfigIPC(GetSandboxFD()))->unref();
 336 }
 337
 338 static bool CreateInitProcessReaper() {
 339   // The current process becomes init(1), this function returns from a
 340   // newly created process.
 341   const bool init_created = sandbox::CreateInitProcessReaper(NULL);
 342   if (!init_created) {
 343     LOG(ERROR) << "Error creating an init process to reap zombies";
 344     return false;
 345   }
 346   return true;
 347 }
 348
 349 // Enter the setuid sandbox. This requires the current process to have been
 350 // created through the setuid sandbox.
 351 static bool EnterSuidSandbox(sandbox::SetuidSandboxClient* setuid_sandbox) {
 352   DCHECK(setuid_sandbox);
 353   DCHECK(setuid_sandbox->IsSuidSandboxChild());
 354
 355   // Use the SUID sandbox.  This still allows the seccomp sandbox to
 356   // be enabled by the process later.
 357
 358   if (!setuid_sandbox->IsSuidSandboxUpToDate()) {
 359     LOG(WARNING) <<
 360         "You are using a wrong version of the setuid binary!\n"
 361         "Please read "
 362         "https://code.google.com/p/chromium/wiki/LinuxSUIDSandboxDevelopment."
 363         "\n\n";
 364   }
 365
 366   if (!setuid_sandbox->ChrootMe())
 367     return false;
 368
 369   if (setuid_sandbox->IsInNewPIDNamespace()) {
 370     CHECK_EQ(1, getpid())
 371         << "The SUID sandbox created a new PID namespace but Zygote "
 372            "is not the init process. Please, make sure the SUID "
 373            "binary is up to date.";
 374   }
 375
 376   if (getpid() == 1) {
 377     // The setuid sandbox has created a new PID namespace and we need
 378     // to assume the role of init.
 379     CHECK(CreateInitProcessReaper());
 380   }
 381
 382 #if !defined(OS_OPENBSD)
 383   // Previously, we required that the binary be non-readable. This causes the
 384   // kernel to mark the process as non-dumpable at startup. The thinking was
 385   // that, although we were putting the renderers into a PID namespace (with
 386   // the SUID sandbox), they would nonetheless be in the /same/ PID
 387   // namespace. So they could ptrace each other unless they were non-dumpable.
 388   //
 389   // If the binary was readable, then there would be a window between process
 390   // startup and the point where we set the non-dumpable flag in which a
 391   // compromised renderer could ptrace attach.
 392   //
 393   // However, now that we have a zygote model, only the (trusted) zygote
 394   // exists at this point and we can set the non-dumpable flag which is
 395   // inherited by all our renderer children.
 396   //
 397   // Note: a non-dumpable process can't be debugged. To debug sandbox-related
 398   // issues, one can specify --allow-sandbox-debugging to let the process be
 399   // dumpable.
 400   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
 401   if (!command_line.HasSwitch(switches::kAllowSandboxDebugging)) {
 402     prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
 403     if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0)) {
 404       LOG(ERROR) << "Failed to set non-dumpable flag";
 405       return false;
 406     }
 407   }
 408 #endif
 409
 410   return true;
 411 }
 412
 413 // If |is_suid_sandbox_child|, then make sure that the setuid sandbox is
 414 // engaged.
 415 static void EnterLayerOneSandbox(LinuxSandbox* linux_sandbox,
 416                                  bool is_suid_sandbox_child) {
 417   DCHECK(linux_sandbox);
 418
 419   ZygotePreSandboxInit();
 420
 421   // Check that the pre-sandbox initialization didn't spawn threads.
 422 #if !defined(THREAD_SANITIZER)
 423   DCHECK(linux_sandbox->IsSingleThreaded());
 424 #endif
 425
 426   sandbox::SetuidSandboxClient* setuid_sandbox =
 427       linux_sandbox->setuid_sandbox_client();
 428
 429   if (is_suid_sandbox_child) {
 430     CHECK(EnterSuidSandbox(setuid_sandbox)) << "Failed to enter setuid sandbox";
 431   }
 432 }
 433
 434 bool ZygoteMain(const MainFunctionParams& params,
 435                 ScopedVector<ZygoteForkDelegate> fork_delegates) {
 436   g_am_zygote_or_renderer = true;
 437   sandbox::InitLibcUrandomOverrides();
 438
 439   LinuxSandbox* linux_sandbox = LinuxSandbox::GetInstance();
 440   // This will pre-initialize the various sandboxes that need it.
 441   linux_sandbox->PreinitializeSandbox();
 442
 443   const bool must_enable_setuid_sandbox =
 444       linux_sandbox->setuid_sandbox_client()->IsSuidSandboxChild();
 445   if (must_enable_setuid_sandbox) {
 446     linux_sandbox->setuid_sandbox_client()->CloseDummyFile();
 447
 448     // Let the ZygoteHost know we're booting up.
 449     CHECK(UnixDomainSocket::SendMsg(kZygoteSocketPairFd,
 450                                     kZygoteBootMessage,
 451                                     sizeof(kZygoteBootMessage),
 452                                     std::vector<int>()));
 453   }
 454
 455   VLOG(1) << "ZygoteMain: initializing " << fork_delegates.size()
 456           << " fork delegates";
 457   for (ScopedVector<ZygoteForkDelegate>::iterator i = fork_delegates.begin();
 458        i != fork_delegates.end();
 459        ++i) {
 460     (*i)->Init(GetSandboxFD(), must_enable_setuid_sandbox);
 461   }
 462
 463   // Turn on the first layer of the sandbox if the configuration warrants it.
 464   EnterLayerOneSandbox(linux_sandbox, must_enable_setuid_sandbox);
 465
 466   int sandbox_flags = linux_sandbox->GetStatus();
 467   bool setuid_sandbox_engaged = sandbox_flags & kSandboxLinuxSUID;
 468   CHECK_EQ(must_enable_setuid_sandbox, setuid_sandbox_engaged);
 469
 470   Zygote zygote(sandbox_flags, fork_delegates.Pass());
 471   // This function call can return multiple times, once per fork().
 472   return zygote.ProcessRequests();
 473 }
 474
 475 }  // namespace content