New NaCl zygote implementation 2

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 <errno.h>
+#include <stdlib.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <vector>
+
+#include "base/at_exit.h"
+#include "base/command_line.h"
+#include "base/eintr_wrapper.h"
+#include "base/logging.h"
+#include "base/message_loop.h"
+#include "base/rand_util.h"
+#include "ipc/ipc_channel.h"
+#include "chrome/common/nacl_helper_linux.h"
+#include "chrome/nacl/nacl_listener.h"
+#include "content/common/child_process_info.h"
+#include "content/common/main_function_params.h"
+#include "content/common/unix_domain_socket_posix.h"
+
+static 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.
+static void BecomeNaClLoader(const std::vector<int>& child_fds) {
+  VLOG(1) << "NaCl loader: setting up IPC descriptor";
+  close(kNaClZygoteDescriptor); // don't need this 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;
+  IPC::Channel channel(ChildProcessInfo::GenerateRandomChannelID(&listener),

[jam, 2011/06/22 00:49:52]

I don't understand how the IPC works if the launched process uses a random
channel id.  What we do is pass the channel name in the command line argument,
and the child process gets it from the current process' command line.

[Brad Chen, 2011/06/22 16:10:31]

I was quite surprised when things worked with a random handle; I was hoping you
would know what was going on. Considering that the previous version with
nacl_launcher_thread.cc never specified or created a handle, it is consistent
that this handle might be ignored.

My hunch is that the actual channel is specified at
content/browser/child_process_launcher.cc:125 when is pushes a mapping for
kPrimaryIPCChannel.

I will spend some more time reading code then drop by to discuss...

On 2011/06/22 00:49:52, John Abd-El-Malek wrote:

+                       IPC::Channel::MODE_CLIENT, &listener);
+  CHECK(channel.Connect());
+  MessageLoop::current()->Run();
+  _exit(0);
+}
+
+// Some of this code was lifted from
+// content/browser/zygote_main_linux.cc:ForkWithRealPid()
+static 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.
+    if (g_suid_sandbox_active) {
+      char buffer[1];
+      // 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.
+      int nread = HANDLE_EINTR(read(child_fds[kNaClParentFDIndex], buffer, 1));
+      if (nread != 1 || buffer[0] != 'x') {
+        if (nread < 0) {
+          perror("read");
+        }
+        LOG(ERROR) << "Failed to synch with zygote: read " << nread;
+      } else {
+        VLOG(1) << "NaCl loader is synchronised with Chrome zygote";
+      }
+    }
+    close(child_fds[kNaClDummyFDIndex]);
+    close(child_fds[kNaClParentFDIndex]);
+    BecomeNaClLoader(child_fds);
+    // 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++) {
+    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";
+  }
+}
+
+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 (kNaClBrowserFDIndex + 1 == fds.size() ||
+          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";
+    }
+  }
+}