| // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| // A mini-zygote specifically for Native Client. |
| |
| #include "chrome/common/nacl_helper_linux.h" |
| |
| #include <errno.h> |
| #include <link.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <sys/socket.h> |
| #include <sys/types.h> |
| |
| #include <string> |
| #include <vector> |
| |
| #include "base/at_exit.h" |
| #include "base/command_line.h" |
| #include "base/eintr_wrapper.h" |
| #include "base/global_descriptors_posix.h" |
| #include "base/json/string_escape.h" |
| #include "base/logging.h" |
| #include "base/message_loop.h" |
| #include "base/posix/unix_domain_socket.h" |
| #include "base/rand_util.h" |
| #include "chrome/nacl/nacl_listener.h" |
| #include "crypto/nss_util.h" |
| #include "ipc/ipc_descriptors.h" |
| #include "ipc/ipc_switches.h" |
| #include "sandbox/linux/services/libc_urandom_override.h" |
| |
| namespace { |
| |
| // The child must mimic the behavior of zygote_main_linux.cc on the child |
| // side of the fork. See zygote_main_linux.cc:HandleForkRequest from |
| // if (!child) { |
| // Note: this code doesn't attempt to support SELINUX or the SECCOMP sandbox. |
| void BecomeNaClLoader(const std::vector<int>& child_fds, |
| size_t prereserved_sandbox_size) { |
| VLOG(1) << "NaCl loader: setting up IPC descriptor"; |
| // don't need zygote FD any more |
| if (HANDLE_EINTR(close(kNaClZygoteDescriptor)) != 0) |
| LOG(ERROR) << "close(kNaClZygoteDescriptor) failed."; |
| // Set up browser descriptor on fd 3 and IPC as expected by Chrome. |
| base::GlobalDescriptors::GetInstance()->Set(kPrimaryIPCChannel, |
| kPrimaryIPCChannel + base::GlobalDescriptors::kBaseDescriptor); |
| int zfd = dup2(child_fds[kNaClBrowserFDIndex], kNaClBrowserDescriptor); |
| if (zfd != kNaClBrowserDescriptor) { |
| LOG(ERROR) << "Could not initialize kNaClBrowserDescriptor"; |
| _exit(-1); |
| } |
| |
| MessageLoopForIO main_message_loop; |
| NaClListener listener; |
| listener.set_prereserved_sandbox_size(prereserved_sandbox_size); |
| listener.Listen(); |
| _exit(0); |
| } |
| |
| // Some of this code was lifted from |
| // content/browser/zygote_main_linux.cc:ForkWithRealPid() |
| void HandleForkRequest(const std::vector<int>& child_fds, |
| size_t prereserved_sandbox_size) { |
| VLOG(1) << "nacl_helper: forking"; |
| pid_t childpid = fork(); |
| if (childpid < 0) { |
| perror("fork"); |
| LOG(ERROR) << "*** HandleForkRequest failed\n"; |
| // fall through to parent case below |
| } else if (childpid == 0) { // In the child process. |
| bool validack = false; |
| const size_t kMaxReadSize = 1024; |
| char buffer[kMaxReadSize]; |
| // Wait until the parent process has discovered our PID. We |
| // should not fork any child processes (which the seccomp |
| // sandbox does) until then, because that can interfere with the |
| // parent's discovery of our PID. |
| const int nread = HANDLE_EINTR(read(child_fds[kNaClParentFDIndex], buffer, |
| kMaxReadSize)); |
| const std::string switch_prefix = std::string("--") + |
| switches::kProcessChannelID + std::string("="); |
| const size_t len = switch_prefix.length(); |
| |
| if (nread < 0) { |
| perror("read"); |
| LOG(ERROR) << "read returned " << nread; |
| } else if (nread > static_cast<int>(len)) { |
| if (switch_prefix.compare(0, len, buffer, 0, len) == 0) { |
| VLOG(1) << "NaCl loader is synchronised with Chrome zygote"; |
| CommandLine::ForCurrentProcess()->AppendSwitchASCII( |
| switches::kProcessChannelID, |
| std::string(&buffer[len], nread - len)); |
| validack = true; |
| } |
| } |
| if (HANDLE_EINTR(close(child_fds[kNaClDummyFDIndex])) != 0) |
| LOG(ERROR) << "close(child_fds[kNaClDummyFDIndex]) failed"; |
| if (HANDLE_EINTR(close(child_fds[kNaClParentFDIndex])) != 0) |
| LOG(ERROR) << "close(child_fds[kNaClParentFDIndex]) failed"; |
| if (validack) { |
| BecomeNaClLoader(child_fds, prereserved_sandbox_size); |
| } else { |
| LOG(ERROR) << "Failed to synch with zygote"; |
| } |
| // NOTREACHED |
| return; |
| } |
| // I am the parent. |
| // First, close the dummy_fd so the sandbox won't find me when |
| // looking for the child's pid in /proc. Also close other fds. |
| for (size_t i = 0; i < child_fds.size(); i++) { |
| if (HANDLE_EINTR(close(child_fds[i])) != 0) |
| LOG(ERROR) << "close(child_fds[i]) failed"; |
| } |
| VLOG(1) << "nacl_helper: childpid is " << childpid; |
| // Now tell childpid to the Chrome zygote. |
| if (HANDLE_EINTR(send(kNaClZygoteDescriptor, |
| &childpid, sizeof(childpid), MSG_EOR)) |
| != sizeof(childpid)) { |
| LOG(ERROR) << "*** send() to zygote failed"; |
| } |
| } |
| |
| } // namespace |
| |
| static const char kNaClHelperReservedAtZero[] = "reserved_at_zero"; |
| static const char kNaClHelperRDebug[] = "r_debug"; |
| |
| /* |
| * Since we were started by nacl_helper_bootstrap rather than in the |
| * usual way, the debugger cannot figure out where our executable |
| * or the dynamic linker or the shared libraries are in memory, |
| * so it won't find any symbols. But we can fake it out to find us. |
| * |
| * The zygote passes --r_debug=0xXXXXXXXXXXXXXXXX. |
| * nacl_helper_bootstrap replaces the Xs with the address of its _r_debug |
| * structure. The debugger will look for that symbol by name to |
| * discover the addresses of key dynamic linker data structures. |
| * Since all it knows about is the original main executable, which |
| * is the bootstrap program, it finds the symbol defined there. The |
| * dynamic linker's structure is somewhere else, but it is filled in |
| * after initialization. The parts that really matter to the |
| * debugger never change. So we just copy the contents of the |
| * dynamic linker's structure into the address provided by the option. |
| * Hereafter, if someone attaches a debugger (or examines a core dump), |
| * the debugger will find all the symbols in the normal way. |
| */ |
| static void CheckRDebug(char *argv0) { |
| std::string r_debug_switch_value = |
| CommandLine::ForCurrentProcess()->GetSwitchValueASCII(kNaClHelperRDebug); |
| if (!r_debug_switch_value.empty()) { |
| char *endp; |
| uintptr_t r_debug_addr = strtoul(r_debug_switch_value.c_str(), &endp, 0); |
| if (r_debug_addr != 0 && *endp == '\0') { |
| struct r_debug *bootstrap_r_debug = (struct r_debug *) r_debug_addr; |
| *bootstrap_r_debug = _r_debug; |
| |
| /* |
| * Since the main executable (the bootstrap program) does not |
| * have a dynamic section, the debugger will not skip the |
| * first element of the link_map list as it usually would for |
| * an executable or PIE that was loaded normally. But the |
| * dynamic linker has set l_name for the PIE to "" as is |
| * normal for the main executable. So the debugger doesn't |
| * know which file it is. Fill in the actual file name, which |
| * came in as our argv[0]. |
| */ |
| struct link_map *l = _r_debug.r_map; |
| if (l->l_name[0] == '\0') |
| l->l_name = argv0; |
| } |
| } |
| } |
| |
| /* |
| * The zygote passes --reserved_at_zero=0xXXXXXXXXXXXXXXXX. |
| * nacl_helper_bootstrap replaces the Xs with the amount of prereserved |
| * sandbox memory. |
| * |
| * CheckReservedAtZero parses the value of the argument reserved_at_zero |
| * and returns the amount of prereserved sandbox memory. |
| */ |
| static size_t CheckReservedAtZero() { |
| size_t prereserved_sandbox_size = 0; |
| std::string reserved_at_zero_switch_value = |
| CommandLine::ForCurrentProcess()->GetSwitchValueASCII( |
| kNaClHelperReservedAtZero); |
| if (!reserved_at_zero_switch_value.empty()) { |
| char *endp; |
| prereserved_sandbox_size = |
| strtoul(reserved_at_zero_switch_value.c_str(), &endp, 0); |
| if (*endp != '\0') |
| LOG(ERROR) << "Could not parse reserved_at_zero argument value of " |
| << reserved_at_zero_switch_value; |
| } |
| return prereserved_sandbox_size; |
| } |
| |
| #if defined(ADDRESS_SANITIZER) |
| // Do not install the SIGSEGV handler in ASan. This should make the NaCl |
| // platform qualification test pass. |
| static const char kAsanDefaultOptionsNaCl[] = "handle_segv=0"; |
| |
| // Override the default ASan options for the NaCl helper. |
| // __asan_default_options should not be instrumented, because it is called |
| // before ASan is initialized. |
| extern "C" |
| __attribute__((no_address_safety_analysis)) |
| const char *__asan_default_options() { |
| return kAsanDefaultOptionsNaCl; |
| } |
| #endif |
| |
| int main(int argc, char *argv[]) { |
| CommandLine::Init(argc, argv); |
| base::AtExitManager exit_manager; |
| base::RandUint64(); // acquire /dev/urandom fd before sandbox is raised |
| #if !defined(CHROMIUM_SELINUX) |
| // Allows NSS to fopen() /dev/urandom. |
| sandbox::InitLibcUrandomOverrides(); |
| #endif |
| #if defined(USE_NSS) |
| // Configure NSS for use inside the NaCl process. |
| // The fork check has not caused problems for NaCl, but this appears to be |
| // best practice (see other places LoadNSSLibraries is called.) |
| crypto::DisableNSSForkCheck(); |
| // Without this line on Linux, HMAC::Init will instantiate a singleton that |
| // in turn attempts to open a file. Disabling this behavior avoids a ~70 ms |
| // stall the first time HMAC is used. |
| crypto::ForceNSSNoDBInit(); |
| // Load shared libraries before sandbox is raised. |
| // NSS is needed to perform hashing for validation caching. |
| crypto::LoadNSSLibraries(); |
| #endif |
| std::vector<int> empty; // for SendMsg() calls |
| size_t prereserved_sandbox_size = CheckReservedAtZero(); |
| |
| CheckRDebug(argv[0]); |
| |
| // Send the zygote a message to let it know we are ready to help |
| if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, |
| kNaClHelperStartupAck, |
| sizeof(kNaClHelperStartupAck), empty)) { |
| LOG(ERROR) << "*** send() to zygote failed"; |
| } |
| |
| while (true) { |
| int badpid = -1; |
| std::vector<int> fds; |
| static const unsigned kMaxMessageLength = 2048; |
| char buf[kMaxMessageLength]; |
| const ssize_t msglen = UnixDomainSocket::RecvMsg(kNaClZygoteDescriptor, |
| &buf, sizeof(buf), &fds); |
| if (msglen == 0 || (msglen == -1 && errno == ECONNRESET)) { |
| // EOF from the browser. Goodbye! |
| _exit(0); |
| } else if (msglen < 0) { |
| LOG(ERROR) << "nacl_helper: receive from zygote failed, errno = " |
| << errno; |
| } else if (msglen == sizeof(kNaClForkRequest) - 1 && |
| memcmp(buf, kNaClForkRequest, msglen) == 0) { |
| if (kNaClParentFDIndex + 1 == fds.size()) { |
| HandleForkRequest(fds, prereserved_sandbox_size); |
| continue; // fork succeeded. Note: child does not return |
| } else { |
| LOG(ERROR) << "nacl_helper: unexpected number of fds, got " |
| << fds.size(); |
| } |
| } else { |
| LOG(ERROR) << "nacl_helper unrecognized request: " |
| << base::GetDoubleQuotedJson(std::string(buf, buf + msglen)); |
| _exit(-1); |
| } |
| // if fork fails, send PID=-1 to zygote |
| if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, &badpid, |
| sizeof(badpid), empty)) { |
| LOG(ERROR) << "*** send() to zygote failed"; |
| } |
| } |
| CHECK(false); // This routine must not return |
| } |