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| 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 // A mini-zygote specifically for Native Client. | |
| 6 | |
| 7 #include "chrome/common/nacl_helper_linux.h" | |
| 8 | |
| 9 #include <errno.h> | |
| 10 #include <fcntl.h> | |
| 11 #include <link.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/json/string_escape.h" | |
| 24 #include "base/logging.h" | |
| 25 #include "base/message_loop.h" | |
| 26 #include "base/posix/eintr_wrapper.h" | |
| 27 #include "base/posix/global_descriptors.h" | |
| 28 #include "base/posix/unix_domain_socket_linux.h" | |
| 29 #include "base/rand_util.h" | |
| 30 #include "chrome/nacl/nacl_listener.h" | |
| 31 #include "crypto/nss_util.h" | |
| 32 #include "ipc/ipc_descriptors.h" | |
| 33 #include "ipc/ipc_switches.h" | |
| 34 #include "sandbox/linux/services/libc_urandom_override.h" | |
| 35 | |
| 36 namespace { | |
| 37 | |
| 38 // The child must mimic the behavior of zygote_main_linux.cc on the child | |
| 39 // side of the fork. See zygote_main_linux.cc:HandleForkRequest from | |
| 40 // if (!child) { | |
| 41 // Note: this code doesn't attempt to support the SECCOMP sandbox. | |
| 42 void BecomeNaClLoader(const std::vector<int>& child_fds, | |
| 43 size_t prereserved_sandbox_size) { | |
| 44 VLOG(1) << "NaCl loader: setting up IPC descriptor"; | |
| 45 // don't need zygote FD any more | |
| 46 if (HANDLE_EINTR(close(kNaClZygoteDescriptor)) != 0) | |
| 47 LOG(ERROR) << "close(kNaClZygoteDescriptor) failed."; | |
| 48 base::GlobalDescriptors::GetInstance()->Set(kPrimaryIPCChannel, | |
| 49 child_fds[kNaClBrowserFDIndex]); | |
| 50 | |
| 51 base::MessageLoopForIO main_message_loop; | |
| 52 NaClListener listener; | |
| 53 listener.set_prereserved_sandbox_size(prereserved_sandbox_size); | |
| 54 listener.Listen(); | |
| 55 _exit(0); | |
| 56 } | |
| 57 | |
| 58 // Some of this code was lifted from | |
| 59 // content/browser/zygote_main_linux.cc:ForkWithRealPid() | |
| 60 void HandleForkRequest(const std::vector<int>& child_fds, | |
| 61 size_t prereserved_sandbox_size) { | |
| 62 VLOG(1) << "nacl_helper: forking"; | |
| 63 pid_t childpid = fork(); | |
| 64 if (childpid < 0) { | |
| 65 perror("fork"); | |
| 66 LOG(ERROR) << "*** HandleForkRequest failed\n"; | |
| 67 // fall through to parent case below | |
| 68 } else if (childpid == 0) { // In the child process. | |
| 69 bool validack = false; | |
| 70 const size_t kMaxReadSize = 1024; | |
| 71 char buffer[kMaxReadSize]; | |
| 72 // Wait until the parent process has discovered our PID. We | |
| 73 // should not fork any child processes (which the seccomp | |
| 74 // sandbox does) until then, because that can interfere with the | |
| 75 // parent's discovery of our PID. | |
| 76 const int nread = HANDLE_EINTR(read(child_fds[kNaClParentFDIndex], buffer, | |
| 77 kMaxReadSize)); | |
| 78 const std::string switch_prefix = std::string("--") + | |
| 79 switches::kProcessChannelID + std::string("="); | |
| 80 const size_t len = switch_prefix.length(); | |
| 81 | |
| 82 if (nread < 0) { | |
| 83 perror("read"); | |
| 84 LOG(ERROR) << "read returned " << nread; | |
| 85 } else if (nread > static_cast<int>(len)) { | |
| 86 if (switch_prefix.compare(0, len, buffer, 0, len) == 0) { | |
| 87 VLOG(1) << "NaCl loader is synchronised with Chrome zygote"; | |
| 88 CommandLine::ForCurrentProcess()->AppendSwitchASCII( | |
| 89 switches::kProcessChannelID, | |
| 90 std::string(&buffer[len], nread - len)); | |
| 91 validack = true; | |
| 92 } | |
| 93 } | |
| 94 if (HANDLE_EINTR(close(child_fds[kNaClDummyFDIndex])) != 0) | |
| 95 LOG(ERROR) << "close(child_fds[kNaClDummyFDIndex]) failed"; | |
| 96 if (HANDLE_EINTR(close(child_fds[kNaClParentFDIndex])) != 0) | |
| 97 LOG(ERROR) << "close(child_fds[kNaClParentFDIndex]) failed"; | |
| 98 if (validack) { | |
| 99 BecomeNaClLoader(child_fds, prereserved_sandbox_size); | |
| 100 } else { | |
| 101 LOG(ERROR) << "Failed to synch with zygote"; | |
| 102 } | |
| 103 // NOTREACHED | |
| 104 return; | |
| 105 } | |
| 106 // I am the parent. | |
| 107 // First, close the dummy_fd so the sandbox won't find me when | |
| 108 // looking for the child's pid in /proc. Also close other fds. | |
| 109 for (size_t i = 0; i < child_fds.size(); i++) { | |
| 110 if (HANDLE_EINTR(close(child_fds[i])) != 0) | |
| 111 LOG(ERROR) << "close(child_fds[i]) failed"; | |
| 112 } | |
| 113 VLOG(1) << "nacl_helper: childpid is " << childpid; | |
| 114 // Now tell childpid to the Chrome zygote. | |
| 115 if (HANDLE_EINTR(send(kNaClZygoteDescriptor, | |
| 116 &childpid, sizeof(childpid), MSG_EOR)) | |
| 117 != sizeof(childpid)) { | |
| 118 LOG(ERROR) << "*** send() to zygote failed"; | |
| 119 } | |
| 120 } | |
| 121 | |
| 122 // This is a poor man's check on whether we are sandboxed. | |
| 123 bool IsSandboxed() { | |
| 124 int proc_fd = open("/proc/self/exe", O_RDONLY); | |
| 125 if (proc_fd >= 0) { | |
| 126 HANDLE_EINTR(close(proc_fd)); | |
| 127 return false; | |
| 128 } | |
| 129 return true; | |
| 130 } | |
| 131 | |
| 132 } // namespace | |
| 133 | |
| 134 static const char kNaClHelperReservedAtZero[] = "reserved_at_zero"; | |
| 135 static const char kNaClHelperRDebug[] = "r_debug"; | |
| 136 | |
| 137 // Since we were started by nacl_helper_bootstrap rather than in the | |
| 138 // usual way, the debugger cannot figure out where our executable | |
| 139 // or the dynamic linker or the shared libraries are in memory, | |
| 140 // so it won't find any symbols. But we can fake it out to find us. | |
| 141 // | |
| 142 // The zygote passes --r_debug=0xXXXXXXXXXXXXXXXX. | |
| 143 // nacl_helper_bootstrap replaces the Xs with the address of its _r_debug | |
| 144 // structure. The debugger will look for that symbol by name to | |
| 145 // discover the addresses of key dynamic linker data structures. | |
| 146 // Since all it knows about is the original main executable, which | |
| 147 // is the bootstrap program, it finds the symbol defined there. The | |
| 148 // dynamic linker's structure is somewhere else, but it is filled in | |
| 149 // after initialization. The parts that really matter to the | |
| 150 // debugger never change. So we just copy the contents of the | |
| 151 // dynamic linker's structure into the address provided by the option. | |
| 152 // Hereafter, if someone attaches a debugger (or examines a core dump), | |
| 153 // the debugger will find all the symbols in the normal way. | |
| 154 static void CheckRDebug(char* argv0) { | |
| 155 std::string r_debug_switch_value = | |
| 156 CommandLine::ForCurrentProcess()->GetSwitchValueASCII(kNaClHelperRDebug); | |
| 157 if (!r_debug_switch_value.empty()) { | |
| 158 char* endp; | |
| 159 uintptr_t r_debug_addr = strtoul(r_debug_switch_value.c_str(), &endp, 0); | |
| 160 if (r_debug_addr != 0 && *endp == '\0') { | |
| 161 r_debug* bootstrap_r_debug = reinterpret_cast<r_debug*>(r_debug_addr); | |
| 162 *bootstrap_r_debug = _r_debug; | |
| 163 | |
| 164 // Since the main executable (the bootstrap program) does not | |
| 165 // have a dynamic section, the debugger will not skip the | |
| 166 // first element of the link_map list as it usually would for | |
| 167 // an executable or PIE that was loaded normally. But the | |
| 168 // dynamic linker has set l_name for the PIE to "" as is | |
| 169 // normal for the main executable. So the debugger doesn't | |
| 170 // know which file it is. Fill in the actual file name, which | |
| 171 // came in as our argv[0]. | |
| 172 link_map* l = _r_debug.r_map; | |
| 173 if (l->l_name[0] == '\0') | |
| 174 l->l_name = argv0; | |
| 175 } | |
| 176 } | |
| 177 } | |
| 178 | |
| 179 // The zygote passes --reserved_at_zero=0xXXXXXXXXXXXXXXXX. | |
| 180 // nacl_helper_bootstrap replaces the Xs with the amount of prereserved | |
| 181 // sandbox memory. | |
| 182 // | |
| 183 // CheckReservedAtZero parses the value of the argument reserved_at_zero | |
| 184 // and returns the amount of prereserved sandbox memory. | |
| 185 static size_t CheckReservedAtZero() { | |
| 186 size_t prereserved_sandbox_size = 0; | |
| 187 std::string reserved_at_zero_switch_value = | |
| 188 CommandLine::ForCurrentProcess()->GetSwitchValueASCII( | |
| 189 kNaClHelperReservedAtZero); | |
| 190 if (!reserved_at_zero_switch_value.empty()) { | |
| 191 char* endp; | |
| 192 prereserved_sandbox_size = | |
| 193 strtoul(reserved_at_zero_switch_value.c_str(), &endp, 0); | |
| 194 if (*endp != '\0') | |
| 195 LOG(ERROR) << "Could not parse reserved_at_zero argument value of " | |
| 196 << reserved_at_zero_switch_value; | |
| 197 } | |
| 198 return prereserved_sandbox_size; | |
| 199 } | |
| 200 | |
| 201 #if defined(ADDRESS_SANITIZER) | |
| 202 // Do not install the SIGSEGV handler in ASan. This should make the NaCl | |
| 203 // platform qualification test pass. | |
| 204 static const char kAsanDefaultOptionsNaCl[] = "handle_segv=0"; | |
| 205 | |
| 206 // Override the default ASan options for the NaCl helper. | |
| 207 // __asan_default_options should not be instrumented, because it is called | |
| 208 // before ASan is initialized. | |
| 209 extern "C" | |
| 210 __attribute__((no_address_safety_analysis)) | |
| 211 const char* __asan_default_options() { | |
| 212 return kAsanDefaultOptionsNaCl; | |
| 213 } | |
| 214 #endif | |
| 215 | |
| 216 int main(int argc, char* argv[]) { | |
| 217 CommandLine::Init(argc, argv); | |
| 218 base::AtExitManager exit_manager; | |
| 219 base::RandUint64(); // acquire /dev/urandom fd before sandbox is raised | |
| 220 // Allows NSS to fopen() /dev/urandom. | |
| 221 sandbox::InitLibcUrandomOverrides(); | |
| 222 #if defined(USE_NSS) | |
| 223 // Configure NSS for use inside the NaCl process. | |
| 224 // The fork check has not caused problems for NaCl, but this appears to be | |
| 225 // best practice (see other places LoadNSSLibraries is called.) | |
| 226 crypto::DisableNSSForkCheck(); | |
| 227 // Without this line on Linux, HMAC::Init will instantiate a singleton that | |
| 228 // in turn attempts to open a file. Disabling this behavior avoids a ~70 ms | |
| 229 // stall the first time HMAC is used. | |
| 230 crypto::ForceNSSNoDBInit(); | |
| 231 // Load shared libraries before sandbox is raised. | |
| 232 // NSS is needed to perform hashing for validation caching. | |
| 233 crypto::LoadNSSLibraries(); | |
| 234 #endif | |
| 235 std::vector<int> empty; // for SendMsg() calls | |
| 236 size_t prereserved_sandbox_size = CheckReservedAtZero(); | |
| 237 | |
| 238 CheckRDebug(argv[0]); | |
| 239 | |
| 240 // Check that IsSandboxed() works. We should not be sandboxed at this point. | |
| 241 CHECK(!IsSandboxed()) << "Unexpectedly sandboxed!"; | |
| 242 | |
| 243 // Send the zygote a message to let it know we are ready to help | |
| 244 if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, | |
| 245 kNaClHelperStartupAck, | |
| 246 sizeof(kNaClHelperStartupAck), empty)) { | |
| 247 LOG(ERROR) << "*** send() to zygote failed"; | |
| 248 } | |
| 249 | |
| 250 while (true) { | |
| 251 int badpid = -1; | |
| 252 std::vector<int> fds; | |
| 253 static const unsigned kMaxMessageLength = 2048; | |
| 254 char buf[kMaxMessageLength]; | |
| 255 const ssize_t msglen = UnixDomainSocket::RecvMsg(kNaClZygoteDescriptor, | |
| 256 &buf, sizeof(buf), &fds); | |
| 257 // If the Zygote has started handling requests, we should be sandboxed via | |
| 258 // the setuid sandbox. | |
| 259 if (!IsSandboxed()) { | |
| 260 LOG(ERROR) << "NaCl helper process running without a sandbox!\n" | |
| 261 << "Most likely you need to configure your SUID sandbox " | |
| 262 << "correctly"; | |
| 263 } | |
| 264 if (msglen == 0 || (msglen == -1 && errno == ECONNRESET)) { | |
| 265 // EOF from the browser. Goodbye! | |
| 266 _exit(0); | |
| 267 } else if (msglen < 0) { | |
| 268 LOG(ERROR) << "nacl_helper: receive from zygote failed, errno = " | |
| 269 << errno; | |
| 270 } else if (msglen == sizeof(kNaClForkRequest) - 1 && | |
| 271 memcmp(buf, kNaClForkRequest, msglen) == 0) { | |
| 272 if (kNaClParentFDIndex + 1 == fds.size()) { | |
| 273 HandleForkRequest(fds, prereserved_sandbox_size); | |
| 274 continue; // fork succeeded. Note: child does not return | |
| 275 } else { | |
| 276 LOG(ERROR) << "nacl_helper: unexpected number of fds, got " | |
| 277 << fds.size(); | |
| 278 } | |
| 279 } else { | |
| 280 LOG(ERROR) << "nacl_helper unrecognized request: " | |
| 281 << base::GetDoubleQuotedJson(std::string(buf, buf + msglen)); | |
| 282 _exit(-1); | |
| 283 } | |
| 284 // if fork fails, send PID=-1 to zygote | |
| 285 if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, &badpid, | |
| 286 sizeof(badpid), empty)) { | |
| 287 LOG(ERROR) << "*** send() to zygote failed"; | |
| 288 } | |
| 289 } | |
| 290 CHECK(false); // This routine must not return | |
| 291 } | |
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Chromium Code Reviews
Issue 16881004:
Move chrome/nacl to components/nacl. (Closed)
Base URL: https://chromium.googlesource.com/chromium/src.git@master