For Linux, create a ZygoteForkDelegate that uses the nacl_helper executable

chrome/nacl/nacl_helper_linux.cc

+// Copyright (c) 2011 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 <stdlib.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <string>
+#include <vector>
+
+#include "base/at_exit.h"
+#include "base/eintr_wrapper.h"
+#include "base/logging.h"
+#include "base/message_loop.h"
+#include "base/rand_util.h"
+#include "chrome/nacl/nacl_listener.h"
+#include "content/common/main_function_params.h"
+#include "content/common/unix_domain_socket_posix.h"
+#include "ipc/ipc_switches.h"
+
+namespace {
+
+bool g_suid_sandbox_active;
+
+// 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) {
+  VLOG(1) << "NaCl loader: setting up IPC descriptor";
+  HANDLE_EINTR(close(kNaClZygoteDescriptor)); // don't need zygote FD any more
+  // Set up browser descriptor as expected by Chrome on fd 3
+  // The zygote takes care of putting the sandbox IPC channel on fd 5
+  int zfd = dup2(child_fds[kNaClBrowserFDIndex], kNaClBrowserDescriptor);
+  if (zfd != kNaClBrowserDescriptor) {
+    LOG(ERROR) << "Could not initialize kNaClBrowserDescriptor";
+    _exit(-1);
+  }
+
+  MessageLoopForIO main_message_loop;
+  NaClListener *listener = new NaClListener();
+  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) {
+  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;
+      }
+    }
+    HANDLE_EINTR(close(child_fds[kNaClDummyFDIndex]));
+    HANDLE_EINTR(close(child_fds[kNaClParentFDIndex]));
+    if (validack) {
+      BecomeNaClLoader(child_fds);
+    } 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++) {
+    HANDLE_EINTR(close(child_fds[i]));
+  }
+  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
+
+int main(int argc, char *argv[]) {
+  CommandLine::Init(argc, argv);
+  base::AtExitManager exit_manager;
+  base::RandUint64();  // acquire /dev/urandom fd before sandbox is raised
+  std::vector<int> empty; // for SendMsg() calls
+
+  g_suid_sandbox_active = (NULL != getenv("SBX_D"));
+
+  // 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);
+    }
+    if (msglen == sizeof(kNaClForkRequest) - 1 &&
+        memcmp(buf, kNaClForkRequest, msglen) == 0) {
+      if (kNaClParentFDIndex + 1 == fds.size()) {
+        HandleForkRequest(fds);
+        continue;  // fork succeeded. Note: child does not return
+      } else {
+        LOG(ERROR) << "nacl_helper: unexpected number of fds, got "
+                   << fds.size();
+      }
+    } else {
+      if (msglen != 0) {
+        LOG(ERROR) << "nacl_helper unrecognized request: %s";
+        _exit(-1);
+      }
+    }
+    // if fork fails, send PID=-1 to zygote
+    if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, &badpid,
+                                   sizeof(badpid), empty)) {
+      LOG(ERROR) << "*** send() to zygote failed";
+    }
+  }
+}