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Side by Side Diff: chrome/nacl/nacl_helper_linux.cc

Issue 16881004: Move chrome/nacl to components/nacl. (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: Create a zygote folder Created 7 years, 5 months ago
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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 "chrome/nacl/nacl_sandbox_linux.h"
32 #include "crypto/nss_util.h"
33 #include "ipc/ipc_descriptors.h"
34 #include "ipc/ipc_switches.h"
35 #include "sandbox/linux/services/libc_urandom_override.h"
36
37 namespace {
38
39 // The child must mimic the behavior of zygote_main_linux.cc on the child
40 // side of the fork. See zygote_main_linux.cc:HandleForkRequest from
41 // if (!child) {
42 void BecomeNaClLoader(const std::vector<int>& child_fds,
43 size_t prereserved_sandbox_size,
44 int number_of_cores) {
45 VLOG(1) << "NaCl loader: setting up IPC descriptor";
46 // don't need zygote FD any more
47 if (HANDLE_EINTR(close(kNaClZygoteDescriptor)) != 0)
48 LOG(ERROR) << "close(kNaClZygoteDescriptor) failed.";
49 bool sandbox_initialized = InitializeBpfSandbox();
50 if (!sandbox_initialized) {
51 LOG(ERROR) << "Could not initialize NaCl's second "
52 << "layer sandbox (seccomp-bpf).";
53 }
54 base::GlobalDescriptors::GetInstance()->Set(kPrimaryIPCChannel,
55 child_fds[kNaClBrowserFDIndex]);
56
57 base::MessageLoopForIO main_message_loop;
58 NaClListener listener;
59 listener.set_prereserved_sandbox_size(prereserved_sandbox_size);
60 listener.set_number_of_cores(number_of_cores);
61 listener.Listen();
62 _exit(0);
63 }
64
65 // Some of this code was lifted from
66 // content/browser/zygote_main_linux.cc:ForkWithRealPid()
67 void HandleForkRequest(const std::vector<int>& child_fds,
68 size_t prereserved_sandbox_size,
69 int number_of_cores) {
70 VLOG(1) << "nacl_helper: forking";
71 pid_t childpid = fork();
72 if (childpid < 0) {
73 perror("fork");
74 LOG(ERROR) << "*** HandleForkRequest failed\n";
75 // fall through to parent case below
76 } else if (childpid == 0) { // In the child process.
77 bool validack = false;
78 const size_t kMaxReadSize = 1024;
79 char buffer[kMaxReadSize];
80 // Wait until the parent process has discovered our PID. We
81 // should not fork any child processes (which the seccomp
82 // sandbox does) until then, because that can interfere with the
83 // parent's discovery of our PID.
84 const int nread = HANDLE_EINTR(read(child_fds[kNaClParentFDIndex], buffer,
85 kMaxReadSize));
86 const std::string switch_prefix = std::string("--") +
87 switches::kProcessChannelID + std::string("=");
88 const size_t len = switch_prefix.length();
89
90 if (nread < 0) {
91 perror("read");
92 LOG(ERROR) << "read returned " << nread;
93 } else if (nread > static_cast<int>(len)) {
94 if (switch_prefix.compare(0, len, buffer, 0, len) == 0) {
95 VLOG(1) << "NaCl loader is synchronised with Chrome zygote";
96 CommandLine::ForCurrentProcess()->AppendSwitchASCII(
97 switches::kProcessChannelID,
98 std::string(&buffer[len], nread - len));
99 validack = true;
100 }
101 }
102 if (HANDLE_EINTR(close(child_fds[kNaClDummyFDIndex])) != 0)
103 LOG(ERROR) << "close(child_fds[kNaClDummyFDIndex]) failed";
104 if (HANDLE_EINTR(close(child_fds[kNaClParentFDIndex])) != 0)
105 LOG(ERROR) << "close(child_fds[kNaClParentFDIndex]) failed";
106 if (validack) {
107 BecomeNaClLoader(child_fds, prereserved_sandbox_size, number_of_cores);
108 } else {
109 LOG(ERROR) << "Failed to synch with zygote";
110 }
111 // NOTREACHED
112 return;
113 }
114 // I am the parent.
115 // First, close the dummy_fd so the sandbox won't find me when
116 // looking for the child's pid in /proc. Also close other fds.
117 for (size_t i = 0; i < child_fds.size(); i++) {
118 if (HANDLE_EINTR(close(child_fds[i])) != 0)
119 LOG(ERROR) << "close(child_fds[i]) failed";
120 }
121 VLOG(1) << "nacl_helper: childpid is " << childpid;
122 // Now tell childpid to the Chrome zygote.
123 if (HANDLE_EINTR(send(kNaClZygoteDescriptor,
124 &childpid, sizeof(childpid), MSG_EOR))
125 != sizeof(childpid)) {
126 LOG(ERROR) << "*** send() to zygote failed";
127 }
128 }
129
130 // This is a poor man's check on whether we are sandboxed.
131 bool IsSandboxed() {
132 int proc_fd = open("/proc/self/exe", O_RDONLY);
133 if (proc_fd >= 0) {
134 HANDLE_EINTR(close(proc_fd));
135 return false;
136 }
137 return true;
138 }
139
140 } // namespace
141
142 static const char kNaClHelperReservedAtZero[] = "reserved_at_zero";
143 static const char kNaClHelperRDebug[] = "r_debug";
144
145 // Since we were started by nacl_helper_bootstrap rather than in the
146 // usual way, the debugger cannot figure out where our executable
147 // or the dynamic linker or the shared libraries are in memory,
148 // so it won't find any symbols. But we can fake it out to find us.
149 //
150 // The zygote passes --r_debug=0xXXXXXXXXXXXXXXXX.
151 // nacl_helper_bootstrap replaces the Xs with the address of its _r_debug
152 // structure. The debugger will look for that symbol by name to
153 // discover the addresses of key dynamic linker data structures.
154 // Since all it knows about is the original main executable, which
155 // is the bootstrap program, it finds the symbol defined there. The
156 // dynamic linker's structure is somewhere else, but it is filled in
157 // after initialization. The parts that really matter to the
158 // debugger never change. So we just copy the contents of the
159 // dynamic linker's structure into the address provided by the option.
160 // Hereafter, if someone attaches a debugger (or examines a core dump),
161 // the debugger will find all the symbols in the normal way.
162 static void CheckRDebug(char* argv0) {
163 std::string r_debug_switch_value =
164 CommandLine::ForCurrentProcess()->GetSwitchValueASCII(kNaClHelperRDebug);
165 if (!r_debug_switch_value.empty()) {
166 char* endp;
167 uintptr_t r_debug_addr = strtoul(r_debug_switch_value.c_str(), &endp, 0);
168 if (r_debug_addr != 0 && *endp == '\0') {
169 r_debug* bootstrap_r_debug = reinterpret_cast<r_debug*>(r_debug_addr);
170 *bootstrap_r_debug = _r_debug;
171
172 // Since the main executable (the bootstrap program) does not
173 // have a dynamic section, the debugger will not skip the
174 // first element of the link_map list as it usually would for
175 // an executable or PIE that was loaded normally. But the
176 // dynamic linker has set l_name for the PIE to "" as is
177 // normal for the main executable. So the debugger doesn't
178 // know which file it is. Fill in the actual file name, which
179 // came in as our argv[0].
180 link_map* l = _r_debug.r_map;
181 if (l->l_name[0] == '\0')
182 l->l_name = argv0;
183 }
184 }
185 }
186
187 // The zygote passes --reserved_at_zero=0xXXXXXXXXXXXXXXXX.
188 // nacl_helper_bootstrap replaces the Xs with the amount of prereserved
189 // sandbox memory.
190 //
191 // CheckReservedAtZero parses the value of the argument reserved_at_zero
192 // and returns the amount of prereserved sandbox memory.
193 static size_t CheckReservedAtZero() {
194 size_t prereserved_sandbox_size = 0;
195 std::string reserved_at_zero_switch_value =
196 CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
197 kNaClHelperReservedAtZero);
198 if (!reserved_at_zero_switch_value.empty()) {
199 char* endp;
200 prereserved_sandbox_size =
201 strtoul(reserved_at_zero_switch_value.c_str(), &endp, 0);
202 if (*endp != '\0')
203 LOG(ERROR) << "Could not parse reserved_at_zero argument value of "
204 << reserved_at_zero_switch_value;
205 }
206 return prereserved_sandbox_size;
207 }
208
209 #if defined(ADDRESS_SANITIZER)
210 // Do not install the SIGSEGV handler in ASan. This should make the NaCl
211 // platform qualification test pass.
212 static const char kAsanDefaultOptionsNaCl[] = "handle_segv=0";
213
214 // Override the default ASan options for the NaCl helper.
215 // __asan_default_options should not be instrumented, because it is called
216 // before ASan is initialized.
217 extern "C"
218 __attribute__((no_address_safety_analysis))
219 const char* __asan_default_options() {
220 return kAsanDefaultOptionsNaCl;
221 }
222 #endif
223
224 int main(int argc, char* argv[]) {
225 CommandLine::Init(argc, argv);
226 base::AtExitManager exit_manager;
227 base::RandUint64(); // acquire /dev/urandom fd before sandbox is raised
228 // Allows NSS to fopen() /dev/urandom.
229 sandbox::InitLibcUrandomOverrides();
230 #if defined(USE_NSS)
231 // Configure NSS for use inside the NaCl process.
232 // The fork check has not caused problems for NaCl, but this appears to be
233 // best practice (see other places LoadNSSLibraries is called.)
234 crypto::DisableNSSForkCheck();
235 // Without this line on Linux, HMAC::Init will instantiate a singleton that
236 // in turn attempts to open a file. Disabling this behavior avoids a ~70 ms
237 // stall the first time HMAC is used.
238 crypto::ForceNSSNoDBInit();
239 // Load shared libraries before sandbox is raised.
240 // NSS is needed to perform hashing for validation caching.
241 crypto::LoadNSSLibraries();
242 #endif
243 std::vector<int> empty; // for SendMsg() calls
244 size_t prereserved_sandbox_size = CheckReservedAtZero();
245 int number_of_cores = sysconf(_SC_NPROCESSORS_ONLN);
246
247 CheckRDebug(argv[0]);
248
249 // Check that IsSandboxed() works. We should not be sandboxed at this point.
250 CHECK(!IsSandboxed()) << "Unexpectedly sandboxed!";
251
252 // Send the zygote a message to let it know we are ready to help
253 if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor,
254 kNaClHelperStartupAck,
255 sizeof(kNaClHelperStartupAck), empty)) {
256 LOG(ERROR) << "*** send() to zygote failed";
257 }
258
259 while (true) {
260 int badpid = -1;
261 std::vector<int> fds;
262 static const unsigned kMaxMessageLength = 2048;
263 char buf[kMaxMessageLength];
264 const ssize_t msglen = UnixDomainSocket::RecvMsg(kNaClZygoteDescriptor,
265 &buf, sizeof(buf), &fds);
266 // If the Zygote has started handling requests, we should be sandboxed via
267 // the setuid sandbox.
268 if (!IsSandboxed()) {
269 LOG(ERROR) << "NaCl helper process running without a sandbox!\n"
270 << "Most likely you need to configure your SUID sandbox "
271 << "correctly";
272 }
273 if (msglen == 0 || (msglen == -1 && errno == ECONNRESET)) {
274 // EOF from the browser. Goodbye!
275 _exit(0);
276 } else if (msglen < 0) {
277 LOG(ERROR) << "nacl_helper: receive from zygote failed, errno = "
278 << errno;
279 } else if (msglen == sizeof(kNaClForkRequest) - 1 &&
280 memcmp(buf, kNaClForkRequest, msglen) == 0) {
281 if (kNaClParentFDIndex + 1 == fds.size()) {
282 HandleForkRequest(fds, prereserved_sandbox_size, number_of_cores);
283 continue; // fork succeeded. Note: child does not return
284 } else {
285 LOG(ERROR) << "nacl_helper: unexpected number of fds, got "
286 << fds.size();
287 }
288 } else {
289 LOG(ERROR) << "nacl_helper unrecognized request: "
290 << base::GetDoubleQuotedJson(std::string(buf, buf + msglen));
291 _exit(-1);
292 }
293 // if fork fails, send PID=-1 to zygote
294 if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, &badpid,
295 sizeof(badpid), empty)) {
296 LOG(ERROR) << "*** send() to zygote failed";
297 }
298 }
299 CHECK(false); // This routine must not return
300 }
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