Linux: don't bother passing the chroot directory fd to the zygote.

chrome/browser/zygote_main_linux.cc

 // Copyright (c) 2009 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.
 
 #include <unistd.h>
 #include <sys/epoll.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/signal.h>
 #include <sys/prctl.h>
@@ skipping 203 matching lines @@
 
     static const char kChrootMe = 'C';
     static const char kChrootMeSuccess = 'O';
 
     if (HANDLE_EINTR(write(fd, &kChrootMe, 1)) != 1) {
       LOG(ERROR) << "Failed to write to chroot pipe: " << errno;
       return false;
     }
 
     char reply;
-    std::vector<int> fds;
-    if (!base::RecvMsg(fd, &reply, 1, &fds)) {
+    if (HANDLE_EINTR(read(fd, &reply, 1)) != 1) {
       LOG(ERROR) << "Failed to read from chroot pipe: " << errno;
       return false;
     }
+
     if (reply != kChrootMeSuccess) {
       LOG(ERROR) << "Error code reply from chroot helper";
-      for (size_t i = 0; i < fds.size(); ++i)
-        HANDLE_EINTR(close(fds[i]));
       return false;
     }
-    if (fds.size() != 1) {
-      LOG(ERROR) << "Bad number of file descriptors from chroot helper";
-      for (size_t i = 0; i < fds.size(); ++i)
-        HANDLE_EINTR(close(fds[i]));
-      return false;
-    }
-    if (fchdir(fds[0]) == -1) {
-      LOG(ERROR) << "Failed to chdir to root directory: " << errno;
-      HANDLE_EINTR(close(fds[0]));
-      return false;
-    }
-    HANDLE_EINTR(close(fds[0]));
 
     static const int kMagicSandboxIPCDescriptor = 5;
     SkiaFontConfigUseIPCImplementation(kMagicSandboxIPCDescriptor);
 
     // Previously, we required that the binary be non-readable. This causes the
     // kernel to mark the process as non-dumpable at startup. The thinking was
     // that, although we were putting the renderers into a PID namespace (with
     // the SUID sandbox), they would nonetheless be in the /same/ PID
     // namespace. So they could ptrace each other unless they were non-dumpable.
     //
@@ skipping 19 matching lines @@
 bool ZygoteMain(const MainFunctionParams& params) {
   if (!MaybeEnterChroot()) {
     LOG(FATAL) << "Failed to enter sandbox. Fail safe abort. (errno: "
                << errno << ")";
     return false;
   }
 
   Zygote zygote;
   return zygote.ProcessRequests();
 }