The Tor Browser: security/sandbox/win/src/sharedmem_ipc

security/sandbox/win/src/sharedmem_ipc_client.cc@6474c204b198 (annotated)

security/sandbox/win/src/sharedmem_ipc_client.cc

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 // Copyright (c) 2006-2008 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 <string.h>
 #include "sandbox/win/src/sharedmem_ipc_client.h"
 #include "sandbox/win/src/sandbox.h"
 #include "sandbox/win/src/crosscall_client.h"
 #include "sandbox/win/src/crosscall_params.h"
 #include "base/logging.h"
 namespace sandbox {
 // Get the base of the data buffer of the channel; this is where the input
 // parameters get serialized. Since they get serialized directly into the
 // channel we avoid one copy.
 void* SharedMemIPCClient::GetBuffer() {
   bool failure = false;
   size_t ix = LockFreeChannel(&failure);
   if (failure) {
     return NULL;
   }
   return reinterpret_cast<char*>(control_) +
          control_->channels[ix].channel_base;
 }
 // If we need to cancel an IPC before issuing DoCall
 // our client should call FreeBuffer with the same pointer
 // returned by GetBuffer.
 void SharedMemIPCClient::FreeBuffer(void* buffer) {
   size_t num = ChannelIndexFromBuffer(buffer);
   ChannelControl* channel = control_->channels;
   LONG result = ::InterlockedExchange(&channel[num].state, kFreeChannel);
   DCHECK(kFreeChannel != result);
   result;
 }
 // The constructor simply casts the shared memory to the internal
 // structures. This is a cheap step that is why this IPC object can
 // and should be constructed per call.
 SharedMemIPCClient::SharedMemIPCClient(void* shared_mem)
     : control_(reinterpret_cast<IPCControl*>(shared_mem)) {
   first_base_ = reinterpret_cast<char*>(shared_mem) +
                control_->channels[0].channel_base;
   // There must be at least one channel.
   DCHECK(0 != control_->channels_count);
 }
 // Do the IPC. At this point the channel should have already been
 // filled with the serialized input parameters.
 // We follow the pattern explained in the header file.
 ResultCode SharedMemIPCClient::DoCall(CrossCallParams* params,
                                       CrossCallReturn* answer) {
   if (!control_->server_alive)
     return SBOX_ERROR_CHANNEL_ERROR;
   size_t num = ChannelIndexFromBuffer(params->GetBuffer());
   ChannelControl* channel = control_->channels;
   // Note that the IPC tag goes outside the buffer as well inside
   // the buffer. This should enable the server to prioritize based on
   // IPC tags without having to de-serialize the entire message.
   channel[num].ipc_tag = params->GetTag();
   // Wait for the server to service this IPC call. After kIPCWaitTimeOut1
   // we check if the server_alive mutex was abandoned which will indicate
   // that the server has died.
   // While the atomic signaling and waiting is not a requirement, it
   // is nice because we save a trip to kernel.
   DWORD wait = ::SignalObjectAndWait(channel[num].ping_event,
                                      channel[num].pong_event,
                                      kIPCWaitTimeOut1, FALSE);
   if (WAIT_TIMEOUT == wait) {
     // The server is taking too long. Enter a loop were we check if the
     // server_alive mutex has been abandoned which would signal a server crash
     // or else we keep waiting for a response.
     while (true) {
       wait = ::WaitForSingleObject(control_->server_alive, 0);
       if (WAIT_TIMEOUT == wait) {
         // Server seems still alive. We already signaled so here we just wait.
         wait = ::WaitForSingleObject(channel[num].pong_event, kIPCWaitTimeOut1);
         if (WAIT_OBJECT_0 == wait) {
           // The server took a long time but responded.
           break;
         } else if (WAIT_TIMEOUT == wait) {
           continue;
         } else {
           return SBOX_ERROR_CHANNEL_ERROR;
         }
       } else {
         // The server has crashed and windows has signaled the mutex as
         // abandoned.
         ::InterlockedExchange(&channel[num].state, kAbandonnedChannel);
         control_->server_alive = 0;
         return SBOX_ERROR_CHANNEL_ERROR;
       }
     }
   } else if (WAIT_OBJECT_0 != wait) {
     // Probably the server crashed before the kIPCWaitTimeOut1 occurred.
     return SBOX_ERROR_CHANNEL_ERROR;
   }
   // The server has returned an answer, copy it and free the channel.
   memcpy(answer, params->GetCallReturn(), sizeof(CrossCallReturn));
   // Return the IPC state It can indicate that while the IPC has
   // completed some error in the Broker has caused to not return valid
   // results.
   return answer->call_outcome;
 }
 // Locking a channel is a simple as looping over all the channels
 // looking for one that is has state = kFreeChannel and atomically
 // swapping it to kBusyChannel.
 // If there is no free channel, then we must back off so some other
 // thread makes progress and frees a channel. To back off we sleep.
 size_t SharedMemIPCClient::LockFreeChannel(bool* severe_failure) {
   if (0 == control_->channels_count) {
     *severe_failure = true;
     return 0;
   }
   ChannelControl* channel = control_->channels;
   do {
     for (size_t ix = 0; ix != control_->channels_count; ++ix) {
       if (kFreeChannel == ::InterlockedCompareExchange(&channel[ix].state,
                                                        kBusyChannel,
                                                        kFreeChannel)) {
           *severe_failure = false;
           return ix;
       }
     }
     // We did not find any available channel, maybe the server is dead.
     DWORD wait = ::WaitForSingleObject(control_->server_alive,
                                        kIPCWaitTimeOut2);
     if (WAIT_TIMEOUT != wait) {
       // The server is dead and we outlive it enough to get in trouble.
       *severe_failure = true;
       return 0;
     }
   }
   while (true);
 }
 // Find out which channel we are from the pointer returned by GetBuffer.
 size_t SharedMemIPCClient::ChannelIndexFromBuffer(const void* buffer) {
   ptrdiff_t d = reinterpret_cast<const char*>(buffer) - first_base_;
   size_t num = d/kIPCChannelSize;
   DCHECK(num < control_->channels_count);
   return (num);
 }
 }  // namespace sandbox

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security/sandbox/win/src/sharedmem_ipc_client.cc@6474c204b198 (annotated)

security/sandbox/win/src/sharedmem_ipc_client.cc