components/nacl/loader/nacl_helper_linux.cc

   1 // Copyright 2013 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 // A mini-zygote specifically for Native Client.
   6
   7 #include "components/nacl/loader/nacl_helper_linux.h"
   8
   9 #include <errno.h>
  10 #include <fcntl.h>
  11 #include <signal.h>
  12 #include <stdio.h>
  13 #include <stdlib.h>
  14 #include <sys/socket.h>
  15 #include <sys/stat.h>
  16 #include <sys/types.h>
  17
  18 #include <string>
  19 #include <vector>
  20
  21 #include "base/at_exit.h"
  22 #include "base/command_line.h"
  23 #include "base/files/scoped_file.h"
  24 #include "base/logging.h"
  25 #include "base/memory/scoped_ptr.h"
  26 #include "base/memory/scoped_vector.h"
  27 #include "base/message_loop/message_loop.h"
  28 #include "base/posix/eintr_wrapper.h"
  29 #include "base/posix/global_descriptors.h"
  30 #include "base/posix/unix_domain_socket_linux.h"
  31 #include "base/process/kill.h"
  32 #include "base/process/process_handle.h"
  33 #include "base/rand_util.h"
  34 #include "components/nacl/common/nacl_switches.h"
  35 #include "components/nacl/loader/nacl_listener.h"
  36 #include "components/nacl/loader/nonsfi/nonsfi_listener.h"
  37 #include "components/nacl/loader/sandbox_linux/nacl_sandbox_linux.h"
  38 #include "content/public/common/content_descriptors.h"
  39 #include "content/public/common/send_zygote_child_ping_linux.h"
  40 #include "content/public/common/zygote_fork_delegate_linux.h"
  41 #include "crypto/nss_util.h"
  42 #include "ipc/ipc_descriptors.h"
  43 #include "ipc/ipc_switches.h"
  44 #include "sandbox/linux/services/credentials.h"
  45 #include "sandbox/linux/services/namespace_sandbox.h"
  46
  47 #if defined(OS_NACL_NONSFI)
  48 #include "native_client/src/public/nonsfi/irt_exception_handling.h"
  49 #else
  50 #include <link.h>
  51 #include "components/nacl/loader/nonsfi/irt_exception_handling.h"
  52 #endif
  53
  54 #if !defined(USE_OPENSSL)
  55 #include "sandbox/linux/services/libc_urandom_override.h"
  56 #endif
  57
  58 namespace {
  59
  60 struct NaClLoaderSystemInfo {
  61   size_t prereserved_sandbox_size;
  62   long number_of_cores;
  63 };
  64
  65 // Replace |file_descriptor| with the reading end of a closed pipe.
  66 void ReplaceFDWithDummy(int file_descriptor) {
  67   // Make sure that file_descriptor is an open descriptor.
  68   PCHECK(-1 != fcntl(file_descriptor, F_GETFD, 0));
  69   int pipefd[2];
  70   PCHECK(0 == pipe(pipefd));
  71   PCHECK(-1 != dup2(pipefd[0], file_descriptor));
  72   PCHECK(0 == IGNORE_EINTR(close(pipefd[0])));
  73   PCHECK(0 == IGNORE_EINTR(close(pipefd[1])));
  74 }
  75
  76 // The child must mimic the behavior of zygote_main_linux.cc on the child
  77 // side of the fork. See zygote_main_linux.cc:HandleForkRequest from
  78 //   if (!child) {
  79 void BecomeNaClLoader(base::ScopedFD browser_fd,
  80                       const NaClLoaderSystemInfo& system_info,
  81                       bool uses_nonsfi_mode,
  82                       nacl::NaClSandbox* nacl_sandbox) {
  83   DCHECK(nacl_sandbox);
  84   VLOG(1) << "NaCl loader: setting up IPC descriptor";
  85   // Close or shutdown IPC channels that we don't need anymore.
  86   PCHECK(0 == IGNORE_EINTR(close(kNaClZygoteDescriptor)));
  87   // In Non-SFI mode, it's important to close any non-expected IPC channels.
  88   if (uses_nonsfi_mode) {
  89     // The low-level kSandboxIPCChannel is used by renderers and NaCl for
  90     // various operations. See the LinuxSandbox::METHOD_* methods. NaCl uses
  91     // LinuxSandbox::METHOD_MAKE_SHARED_MEMORY_SEGMENT in SFI mode, so this
  92     // should only be closed in Non-SFI mode.
  93     // This file descriptor is insidiously used by a number of APIs. Closing it
  94     // could lead to difficult to debug issues. Instead of closing it, replace
  95     // it with a dummy.
  96     const int sandbox_ipc_channel =
  97         base::GlobalDescriptors::kBaseDescriptor + kSandboxIPCChannel;
  98
  99     ReplaceFDWithDummy(sandbox_ipc_channel);
 100
 101     // Install crash signal handlers before disallowing system calls.
 102 #if defined(OS_NACL_NONSFI)
 103     nonsfi_initialize_signal_handler();
 104 #else
 105     nacl::nonsfi::InitializeSignalHandler();
 106 #endif
 107   }
 108
 109   // Always ignore SIGPIPE, for consistency with other Chrome processes and
 110   // because some IPC code, such as sync_socket_posix.cc, requires this.
 111   // We do this before seccomp-bpf is initialized.
 112   PCHECK(signal(SIGPIPE, SIG_IGN) != SIG_ERR);
 113
 114   // Finish layer-1 sandbox initialization and initialize the layer-2 sandbox.
 115   CHECK(!nacl_sandbox->HasOpenDirectory());
 116   nacl_sandbox->InitializeLayerTwoSandbox(uses_nonsfi_mode);
 117   nacl_sandbox->SealLayerOneSandbox();
 118   nacl_sandbox->CheckSandboxingStateWithPolicy();
 119
 120   base::GlobalDescriptors::GetInstance()->Set(kPrimaryIPCChannel,
 121                                               browser_fd.release());
 122
 123   base::MessageLoopForIO main_message_loop;
 124 #if defined(OS_NACL_NONSFI)
 125   CHECK(uses_nonsfi_mode);
 126   nacl::nonsfi::NonSfiListener listener;
 127   listener.Listen();
 128 #else
 129   CHECK(!uses_nonsfi_mode);
 130   NaClListener listener;
 131   listener.set_prereserved_sandbox_size(system_info.prereserved_sandbox_size);
 132   listener.set_number_of_cores(system_info.number_of_cores);
 133   listener.Listen();
 134 #endif
 135   _exit(0);
 136 }
 137
 138 // Start the NaCl loader in a child created by the NaCl loader Zygote.
 139 void ChildNaClLoaderInit(ScopedVector<base::ScopedFD> child_fds,
 140                          const NaClLoaderSystemInfo& system_info,
 141                          bool uses_nonsfi_mode,
 142                          nacl::NaClSandbox* nacl_sandbox,
 143                          const std::string& channel_id) {
 144   DCHECK(child_fds.size() >
 145          std::max(content::ZygoteForkDelegate::kPIDOracleFDIndex,
 146                   content::ZygoteForkDelegate::kBrowserFDIndex));
 147
 148   // Ping the PID oracle socket.
 149   CHECK(content::SendZygoteChildPing(
 150       child_fds[content::ZygoteForkDelegate::kPIDOracleFDIndex]->get()));
 151
 152   base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
 153       switches::kProcessChannelID, channel_id);
 154
 155   // Save the browser socket and close the rest.
 156   base::ScopedFD browser_fd(
 157       child_fds[content::ZygoteForkDelegate::kBrowserFDIndex]->Pass());
 158   child_fds.clear();
 159
 160   BecomeNaClLoader(
 161       browser_fd.Pass(), system_info, uses_nonsfi_mode, nacl_sandbox);
 162   _exit(1);
 163 }
 164
 165 // Handle a fork request from the Zygote.
 166 // Some of this code was lifted from
 167 // content/browser/zygote_main_linux.cc:ForkWithRealPid()
 168 bool HandleForkRequest(ScopedVector<base::ScopedFD> child_fds,
 169                        const NaClLoaderSystemInfo& system_info,
 170                        nacl::NaClSandbox* nacl_sandbox,
 171                        base::PickleIterator* input_iter,
 172                        base::Pickle* output_pickle) {
 173   bool uses_nonsfi_mode;
 174   if (!input_iter->ReadBool(&uses_nonsfi_mode)) {
 175     LOG(ERROR) << "Could not read uses_nonsfi_mode status";
 176     return false;
 177   }
 178
 179   std::string channel_id;
 180   if (!input_iter->ReadString(&channel_id)) {
 181     LOG(ERROR) << "Could not read channel_id string";
 182     return false;
 183   }
 184
 185   if (content::ZygoteForkDelegate::kNumPassedFDs != child_fds.size()) {
 186     LOG(ERROR) << "nacl_helper: unexpected number of fds, got "
 187         << child_fds.size();
 188     return false;
 189   }
 190
 191   VLOG(1) << "nacl_helper: forking";
 192   pid_t child_pid;
 193   if (sandbox::NamespaceSandbox::InNewUserNamespace()) {
 194     child_pid = sandbox::NamespaceSandbox::ForkInNewPidNamespace(
 195         /*drop_capabilities_in_child=*/true);
 196   } else {
 197     child_pid = sandbox::Credentials::ForkAndDropCapabilitiesInChild();
 198   }
 199
 200   if (child_pid < 0) {
 201     PLOG(ERROR) << "*** fork() failed.";
 202   }
 203
 204   if (child_pid == 0) {
 205     // Install termiantion signal handlers for nonsfi NaCl. The SFI NaCl runtime
 206     // will install signal handlers for SIGINT, SIGTERM, etc. so we do not need
 207     // to install termination signal handlers ourselves (in fact, it will crash
 208     // if signal handlers for these are present).
 209     if (uses_nonsfi_mode && getpid() == 1) {
 210       // Note that nonsfi NaCl may override some of these signal handlers, which
 211       // is fine.
 212       sandbox::NamespaceSandbox::InstallDefaultTerminationSignalHandlers();
 213     }
 214     ChildNaClLoaderInit(child_fds.Pass(),
 215                         system_info,
 216                         uses_nonsfi_mode,
 217                         nacl_sandbox,
 218                         channel_id);
 219     NOTREACHED();
 220   }
 221
 222   // I am the parent.
 223   // First, close the dummy_fd so the sandbox won't find me when
 224   // looking for the child's pid in /proc. Also close other fds.
 225   child_fds.clear();
 226   VLOG(1) << "nacl_helper: child_pid is " << child_pid;
 227
 228   // Now send child_pid (eventually -1 if fork failed) to the Chrome Zygote.
 229   output_pickle->WriteInt(child_pid);
 230   return true;
 231 }
 232
 233 bool HandleGetTerminationStatusRequest(base::PickleIterator* input_iter,
 234                                        base::Pickle* output_pickle) {
 235   pid_t child_to_wait;
 236   if (!input_iter->ReadInt(&child_to_wait)) {
 237     LOG(ERROR) << "Could not read pid to wait for";
 238     return false;
 239   }
 240
 241   bool known_dead;
 242   if (!input_iter->ReadBool(&known_dead)) {
 243     LOG(ERROR) << "Could not read known_dead status";
 244     return false;
 245   }
 246   // TODO(jln): With NaCl, known_dead seems to never be set to true (unless
 247   // called from the Zygote's kZygoteCommandReap command). This means that we
 248   // will sometimes detect the process as still running when it's not. Fix
 249   // this!
 250
 251   int exit_code;
 252   base::TerminationStatus status;
 253   if (known_dead)
 254     status = base::GetKnownDeadTerminationStatus(child_to_wait, &exit_code);
 255   else
 256     status = base::GetTerminationStatus(child_to_wait, &exit_code);
 257   output_pickle->WriteInt(static_cast<int>(status));
 258   output_pickle->WriteInt(exit_code);
 259   return true;
 260 }
 261
 262 // Honor a command |command_type|. Eventual command parameters are
 263 // available in |input_iter| and eventual file descriptors attached to
 264 // the command are in |attached_fds|.
 265 // Reply to the command on |reply_fds|.
 266 bool HonorRequestAndReply(int reply_fd,
 267                           int command_type,
 268                           ScopedVector<base::ScopedFD> attached_fds,
 269                           const NaClLoaderSystemInfo& system_info,
 270                           nacl::NaClSandbox* nacl_sandbox,
 271                           base::PickleIterator* input_iter) {
 272   base::Pickle write_pickle;
 273   bool have_to_reply = false;
 274   // Commands must write anything to send back to |write_pickle|.
 275   switch (command_type) {
 276     case nacl::kNaClForkRequest:
 277       have_to_reply = HandleForkRequest(attached_fds.Pass(),
 278                                         system_info,
 279                                         nacl_sandbox,
 280                                         input_iter,
 281                                         &write_pickle);
 282       break;
 283     case nacl::kNaClGetTerminationStatusRequest:
 284       have_to_reply =
 285           HandleGetTerminationStatusRequest(input_iter, &write_pickle);
 286       break;
 287     default:
 288       LOG(ERROR) << "Unsupported command from Zygote";
 289       return false;
 290   }
 291   if (!have_to_reply)
 292     return false;
 293   const std::vector<int> empty;  // We never send file descriptors back.
 294   if (!base::UnixDomainSocket::SendMsg(reply_fd, write_pickle.data(),
 295                                        write_pickle.size(), empty)) {
 296     LOG(ERROR) << "*** send() to zygote failed";
 297     return false;
 298   }
 299   return true;
 300 }
 301
 302 // Read a request from the Zygote from |zygote_ipc_fd| and handle it.
 303 // Die on EOF from |zygote_ipc_fd|.
 304 bool HandleZygoteRequest(int zygote_ipc_fd,
 305                          const NaClLoaderSystemInfo& system_info,
 306                          nacl::NaClSandbox* nacl_sandbox) {
 307   ScopedVector<base::ScopedFD> fds;
 308   char buf[kNaClMaxIPCMessageLength];
 309   const ssize_t msglen = base::UnixDomainSocket::RecvMsg(zygote_ipc_fd,
 310       &buf, sizeof(buf), &fds);
 311   // If the Zygote has started handling requests, we should be sandboxed via
 312   // the setuid sandbox.
 313   if (!nacl_sandbox->layer_one_enabled()) {
 314     LOG(ERROR) << "NaCl helper process running without a sandbox!\n"
 315       << "Most likely you need to configure your SUID sandbox "
 316       << "correctly";
 317   }
 318   if (msglen == 0 || (msglen == -1 && errno == ECONNRESET)) {
 319     // EOF from the browser. Goodbye!
 320     _exit(0);
 321   }
 322   if (msglen < 0) {
 323     PLOG(ERROR) << "nacl_helper: receive from zygote failed";
 324     return false;
 325   }
 326
 327   base::Pickle read_pickle(buf, msglen);
 328   base::PickleIterator read_iter(read_pickle);
 329   int command_type;
 330   if (!read_iter.ReadInt(&command_type)) {
 331     LOG(ERROR) << "Unable to read command from Zygote";
 332     return false;
 333   }
 334   return HonorRequestAndReply(zygote_ipc_fd,
 335                               command_type,
 336                               fds.Pass(),
 337                               system_info,
 338                               nacl_sandbox,
 339                               &read_iter);
 340 }
 341
 342 #if !defined(OS_NACL_NONSFI)
 343 static const char kNaClHelperReservedAtZero[] = "reserved_at_zero";
 344 static const char kNaClHelperRDebug[] = "r_debug";
 345
 346 // Since we were started by nacl_helper_bootstrap rather than in the
 347 // usual way, the debugger cannot figure out where our executable
 348 // or the dynamic linker or the shared libraries are in memory,
 349 // so it won't find any symbols.  But we can fake it out to find us.
 350 //
 351 // The zygote passes --r_debug=0xXXXXXXXXXXXXXXXX.
 352 // nacl_helper_bootstrap replaces the Xs with the address of its _r_debug
 353 // structure.  The debugger will look for that symbol by name to
 354 // discover the addresses of key dynamic linker data structures.
 355 // Since all it knows about is the original main executable, which
 356 // is the bootstrap program, it finds the symbol defined there.  The
 357 // dynamic linker's structure is somewhere else, but it is filled in
 358 // after initialization.  The parts that really matter to the
 359 // debugger never change.  So we just copy the contents of the
 360 // dynamic linker's structure into the address provided by the option.
 361 // Hereafter, if someone attaches a debugger (or examines a core dump),
 362 // the debugger will find all the symbols in the normal way.
 363 //
 364 // Non-SFI mode does not use nacl_helper_bootstrap, so it doesn't need to
 365 // process the --r_debug option.
 366 static void CheckRDebug(char* argv0) {
 367   std::string r_debug_switch_value =
 368       base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 369           kNaClHelperRDebug);
 370   if (!r_debug_switch_value.empty()) {
 371     char* endp;
 372     uintptr_t r_debug_addr = strtoul(r_debug_switch_value.c_str(), &endp, 0);
 373     if (r_debug_addr != 0 && *endp == '\0') {
 374       r_debug* bootstrap_r_debug = reinterpret_cast<r_debug*>(r_debug_addr);
 375       *bootstrap_r_debug = _r_debug;
 376
 377       // Since the main executable (the bootstrap program) does not
 378       // have a dynamic section, the debugger will not skip the
 379       // first element of the link_map list as it usually would for
 380       // an executable or PIE that was loaded normally.  But the
 381       // dynamic linker has set l_name for the PIE to "" as is
 382       // normal for the main executable.  So the debugger doesn't
 383       // know which file it is.  Fill in the actual file name, which
 384       // came in as our argv[0].
 385       link_map* l = _r_debug.r_map;
 386       if (l->l_name[0] == '\0')
 387         l->l_name = argv0;
 388     }
 389   }
 390 }
 391
 392 // The zygote passes --reserved_at_zero=0xXXXXXXXXXXXXXXXX.
 393 // nacl_helper_bootstrap replaces the Xs with the amount of prereserved
 394 // sandbox memory.
 395 //
 396 // CheckReservedAtZero parses the value of the argument reserved_at_zero
 397 // and returns the amount of prereserved sandbox memory.
 398 static size_t CheckReservedAtZero() {
 399   size_t prereserved_sandbox_size = 0;
 400   std::string reserved_at_zero_switch_value =
 401       base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 402           kNaClHelperReservedAtZero);
 403   if (!reserved_at_zero_switch_value.empty()) {
 404     char* endp;
 405     prereserved_sandbox_size =
 406         strtoul(reserved_at_zero_switch_value.c_str(), &endp, 0);
 407     if (*endp != '\0')
 408       LOG(ERROR) << "Could not parse reserved_at_zero argument value of "
 409                  << reserved_at_zero_switch_value;
 410   }
 411   return prereserved_sandbox_size;
 412 }
 413 #endif
 414
 415 }  // namespace
 416
 417 #if defined(ADDRESS_SANITIZER)
 418 // Do not install the SIGSEGV handler in ASan. This should make the NaCl
 419 // platform qualification test pass.
 420 // detect_odr_violation=0: http://crbug.com/376306
 421 static const char kAsanDefaultOptionsNaCl[] =
 422     "handle_segv=0:detect_odr_violation=0";
 423
 424 // Override the default ASan options for the NaCl helper.
 425 // __asan_default_options should not be instrumented, because it is called
 426 // before ASan is initialized.
 427 extern "C"
 428 __attribute__((no_sanitize_address))
 429 // The function isn't referenced from the executable itself. Make sure it isn't
 430 // stripped by the linker.
 431 __attribute__((used))
 432 __attribute__((visibility("default")))
 433 const char* __asan_default_options() {
 434   return kAsanDefaultOptionsNaCl;
 435 }
 436 #endif
 437
 438 int main(int argc, char* argv[]) {
 439   base::CommandLine::Init(argc, argv);
 440   base::AtExitManager exit_manager;
 441   base::RandUint64();  // acquire /dev/urandom fd before sandbox is raised
 442
 443   // NSS is only needed for SFI NaCl.
 444 #if !defined(OS_NACL_NONSFI) && !defined(USE_OPENSSL)
 445   // Allows NSS to fopen() /dev/urandom.
 446   sandbox::InitLibcUrandomOverrides();
 447   // Configure NSS for use inside the NaCl process.
 448   // The fork check has not caused problems for NaCl, but this appears to be
 449   // best practice (see other places LoadNSSLibraries is called.)
 450   crypto::DisableNSSForkCheck();
 451   // Without this line on Linux, HMAC::Init will instantiate a singleton that
 452   // in turn attempts to open a file.  Disabling this behavior avoids a ~70 ms
 453   // stall the first time HMAC is used.
 454   crypto::ForceNSSNoDBInit();
 455   // Load shared libraries before sandbox is raised.
 456   // NSS is needed to perform hashing for validation caching.
 457   crypto::LoadNSSLibraries();
 458 #endif  // !defined(OS_NACL_NONSFI) && !defined(USE_OPENSSL)
 459   const NaClLoaderSystemInfo system_info = {
 460 #if !defined(OS_NACL_NONSFI)
 461     // These are not used by nacl_helper_nonsfi.
 462     CheckReservedAtZero(),
 463     sysconf(_SC_NPROCESSORS_ONLN)
 464 #endif
 465   };
 466
 467 #if !defined(OS_NACL_NONSFI)
 468   CheckRDebug(argv[0]);
 469 #endif
 470
 471   scoped_ptr<nacl::NaClSandbox> nacl_sandbox(new nacl::NaClSandbox);
 472   // Make sure that the early initialization did not start any spurious
 473   // threads.
 474 #if !defined(THREAD_SANITIZER)
 475   CHECK(nacl_sandbox->IsSingleThreaded());
 476 #endif
 477
 478   const bool is_init_process = 1 == getpid();
 479   nacl_sandbox->InitializeLayerOneSandbox();
 480   CHECK_EQ(is_init_process, nacl_sandbox->layer_one_enabled());
 481
 482   const std::vector<int> empty;
 483   // Send the zygote a message to let it know we are ready to help
 484   if (!base::UnixDomainSocket::SendMsg(kNaClZygoteDescriptor,
 485                                        kNaClHelperStartupAck,
 486                                        sizeof(kNaClHelperStartupAck), empty)) {
 487     LOG(ERROR) << "*** send() to zygote failed";
 488   }
 489
 490   // Now handle requests from the Zygote.
 491   while (true) {
 492     bool request_handled = HandleZygoteRequest(
 493         kNaClZygoteDescriptor, system_info, nacl_sandbox.get());
 494     // Do not turn this into a CHECK() without thinking about robustness
 495     // against malicious IPC requests.
 496     DCHECK(request_handled);
 497   }
 498   NOTREACHED();
 499 }