NaCl Sandbox: close low-level IPC channel in Non-SFI mode

components/nacl/loader/nacl_helper_linux.cc

 // Copyright 2013 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 "components/nacl/loader/nacl_helper_linux.h"
 
 #include <errno.h>
 #include <fcntl.h>
@@ skipping 16 matching lines @@
 #include "base/posix/eintr_wrapper.h"
 #include "base/posix/global_descriptors.h"
 #include "base/posix/unix_domain_socket_linux.h"
 #include "base/process/kill.h"
 #include "base/process/process_handle.h"
 #include "base/rand_util.h"
 #include "components/nacl/common/nacl_switches.h"
 #include "components/nacl/loader/nacl_listener.h"
 #include "components/nacl/loader/nacl_sandbox_linux.h"
 #include "components/nacl/loader/nonsfi/nonsfi_sandbox.h"
+#include "content/public/common/content_descriptors.h"
 #include "content/public/common/zygote_fork_delegate_linux.h"
 #include "crypto/nss_util.h"
 #include "ipc/ipc_descriptors.h"
 #include "ipc/ipc_switches.h"
 #include "sandbox/linux/services/credentials.h"
 #include "sandbox/linux/services/libc_urandom_override.h"
 #include "sandbox/linux/services/thread_helpers.h"
 #include "sandbox/linux/suid/client/setuid_sandbox_client.h"
 
 namespace {
@@ skipping 59 matching lines @@
     }
   } else {
     const bool bpf_sandbox_initialized = InitializeBPFSandbox();
     if (!bpf_sandbox_initialized) {
       LOG(ERROR) << "Could not initialize NaCl's second "
                  << "layer sandbox (seccomp-bpf) for SFI mode.";
     }
   }
 }
 
+// Replace |file_descriptor| with the reading end of a closed pipe.
+void ReplaceFDWithDummy(int file_descriptor) {
+  // Make sure that file_descriptor is an open descriptor.
+  PCHECK(-1 != fcntl(file_descriptor, F_GETFD, 0));
+  int pipefd[2];
+  PCHECK(0 == pipe(pipefd));
+  PCHECK(-1 != dup2(pipefd[0], file_descriptor));
+  PCHECK(0 == IGNORE_EINTR(close(pipefd[0])));
+  PCHECK(0 == IGNORE_EINTR(close(pipefd[1])));
+}
+
 // 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) {
 void BecomeNaClLoader(const std::vector<int>& child_fds,
                       const NaClLoaderSystemInfo& system_info,
                       bool uses_nonsfi_mode) {
   VLOG(1) << "NaCl loader: setting up IPC descriptor";
-  // don't need zygote FD any more
-  if (IGNORE_EINTR(close(kNaClZygoteDescriptor)) != 0)
-    LOG(ERROR) << "close(kNaClZygoteDescriptor) failed.";
+  // Close or shutdown IPC channels that we don't need anymore.
+  PCHECK(0 == IGNORE_EINTR(close(kNaClZygoteDescriptor)));
+  // In Non-SFI mode, it's important to close any non-expected IPC channels.
+  if (uses_nonsfi_mode) {
+    // The low-level kSandboxIPCChannel is used by renderers and NaCl for
+    // various operations. See the LinuxSandbox::METHOD_* methods. NaCl uses
+    // LinuxSandbox::METHOD_MAKE_SHARED_MEMORY_SEGMENT in SFI mode, so this
+    // should only be close in Non-SFI mode.

[Mark Seaborn, 2014/04/25 22:59:55]

"closed"

[jln (very slow on Chromium), 2014/04/25 23:40:55]

Done.

+    // This file descriptor is insidiously used by a number of APIs. Closing it
+    // could lead to difficult to debug issues. Instead of closing it, replace
+    // it with a dummy.
+    const int sandbox_ipc_channel =
+        base::GlobalDescriptors::kBaseDescriptor + kSandboxIPCChannel;
+
+    ReplaceFDWithDummy(sandbox_ipc_channel);
+  }
+
   InitializeLayerTwoSandbox(uses_nonsfi_mode);
   base::GlobalDescriptors::GetInstance()->Set(
       kPrimaryIPCChannel,
       child_fds[content::ZygoteForkDelegate::kBrowserFDIndex]);
 
   base::MessageLoopForIO main_message_loop;
   NaClListener listener;
   listener.set_uses_nonsfi_mode(uses_nonsfi_mode);
   listener.set_prereserved_sandbox_size(system_info.prereserved_sandbox_size);
   listener.set_number_of_cores(system_info.number_of_cores);
@@ skipping 327 matching lines @@
   // Now handle requests from the Zygote.
   while (true) {
     bool request_handled = HandleZygoteRequest(kNaClZygoteDescriptor,
                                                system_info);
     // Do not turn this into a CHECK() without thinking about robustness
     // against malicious IPC requests.
     DCHECK(request_handled);
   }
   NOTREACHED();
 }