Chromoting: Implemented security attention sequence (SAS) emulation on Windows.

remoting/host/wts_session_process_launcher_win.cc

 // Copyright (c) 2012 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.
 //
 // This file implements the Windows service controlling Me2Me host processes
 // running within user sessions.
 
 #include "remoting/host/wts_session_process_launcher_win.h"
 
 #include <windows.h>
+#include <sddl.h>
+#include <limits>
 
 #include "base/logging.h"
+#include "base/process_util.h"
+#include "base/rand_util.h"
+#include "base/string16.h"
+#include "base/stringprintf.h"
+#include "base/threading/thread.h"
 #include "base/utf_string_conversions.h"
 #include "base/win/scoped_handle.h"
+#include "ipc/ipc_channel_proxy.h"
+#include "ipc/ipc_message.h"
+#include "ipc/ipc_message_macros.h"
 
+#include "remoting/host/chromoting_messages.h"
+#include "remoting/host/sas_injector.h"
 #include "remoting/host/wts_console_monitor_win.h"
 
 using base::win::ScopedHandle;
 using base::TimeDelta;
 
 namespace {
 
 // The minimum and maximum delays between attempts to inject host process into
 // a session.
 const int kMaxLaunchDelaySeconds = 60;
 const int kMinLaunchDelaySeconds = 1;
 
 // Name of the default session desktop.
 const char kDefaultDesktopName[] = "winsta0\\default";
 
+// Match the pipe name prefix used by Chrome IPC channels.
+const char kChromePipeNamePrefix[] = "\\\\.\\pipe\\chrome.";
+
+// Generates the command line of the host process.
+const char kHostProcessCommandLineFormat[] = "\"%ls\" --channel=%ls";
+
+// The security descriptor of the Chromoting IPC channel. It gives full access
+// to LocalSystem and denies access by anyone else.
+const char kChromotingChannelSecurityDescriptor[] =
+    "O:SY" "G:SY" "D:(A;;GA;;;SY)";
+
 // Takes the process token and makes a copy of it. The returned handle will have
 // |desired_access| rights.
 bool CopyProcessToken(DWORD desired_access,
                       ScopedHandle* token_out) {
 
   HANDLE handle;
   if (!OpenProcessToken(GetCurrentProcess(),
                         TOKEN_DUPLICATE | desired_access,
                         &handle)) {
     LOG_GETLASTERROR(ERROR) << "Failed to open process token";
@@ skipping 66 matching lines @@
                            sizeof(new_session_id))) {
     LOG_GETLASTERROR(ERROR) <<
         "Failed to change session ID of a token";
     return false;
   }
 
   token_out->Set(session_token.Take());
   return true;
 }
 
+// Generates random channel ID.
+// N.B. Stolen from src/content/common/child_process_host_impl.cc
+string16 GenerateRandomChannelId(void* instance) {
+  return base::StringPrintf(ASCIIToUTF16("%d.%p.%d").c_str(),
+                            base::GetCurrentProcId(), instance,
+                            base::RandInt(0, std::numeric_limits<int>::max()));
+}
+
+// Creates the server end of the Chromoting IPC channel.
+// N.B. This code is based on IPC::Channel's implementation.
+bool CreatePipeForIpcChannel(void* instance,
+                             string16* channel_name_out,
+                             ScopedHandle* pipe_out) {
+  // Create security descriptor for the channel.
+  SECURITY_ATTRIBUTES security_attributes;
+  security_attributes.nLength = sizeof(security_attributes);
+  security_attributes.bInheritHandle = FALSE;
+
+  ULONG security_descriptor_length = 0;
+  if (!ConvertStringSecurityDescriptorToSecurityDescriptorA(
+           kChromotingChannelSecurityDescriptor,
+           SDDL_REVISION_1,
+           reinterpret_cast<PSECURITY_DESCRIPTOR*>(
+               &security_attributes.lpSecurityDescriptor),
+           &security_descriptor_length)) {
+    LOG_GETLASTERROR(ERROR) <<
+        "Failed to create a security descriptor for the Chromoting IPC channel";
+    return false;
+  }
+
+  // Generate a random channel name.
+  string16 channel_name(GenerateRandomChannelId(instance));
+
+  // Convert it to the pipe name.
+  string16 pipe_name(ASCIIToUTF16(kChromePipeNamePrefix));
+  pipe_name.append(channel_name);
+
+  // Create the server end of the pipe. This code should match the code in
+  // IPC::Channel with exception of passing a non-default security descriptor.
+  HANDLE pipe = CreateNamedPipeW(pipe_name.c_str(),
+                                 PIPE_ACCESS_DUPLEX | FILE_FLAG_OVERLAPPED |
+                                     FILE_FLAG_FIRST_PIPE_INSTANCE,
+                                 PIPE_TYPE_BYTE | PIPE_READMODE_BYTE,
+                                 1,
+                                 IPC::Channel::kReadBufferSize,
+                                 IPC::Channel::kReadBufferSize,
+                                 5000,
+                                 &security_attributes);
+  if (pipe == INVALID_HANDLE_VALUE) {
+    LOG_GETLASTERROR(ERROR) <<
+        "Failed to create the server end of the Chromoting IPC channel";
+    LocalFree(security_attributes.lpSecurityDescriptor);
+    return false;
+  }
+
+  LocalFree(security_attributes.lpSecurityDescriptor);
+
+  *channel_name_out = channel_name;
+  pipe_out->Set(pipe);
+  return true;
+}
+
 // Launches |binary| in the security context of the supplied |user_token|.
 bool LaunchProcessAsUser(const FilePath& binary,
+                         const string16& command_line,
                          HANDLE user_token,
                          base::Process* process_out) {
-  string16 command_line = binary.value();
+  string16 application_name = binary.value();
   string16 desktop = ASCIIToUTF16(kDefaultDesktopName);
 
   PROCESS_INFORMATION process_info;
   STARTUPINFOW startup_info;
 
   memset(&startup_info, 0, sizeof(startup_info));
   startup_info.cb = sizeof(startup_info);
   startup_info.lpDesktop = const_cast<LPWSTR>(desktop.c_str());
 
   if (!CreateProcessAsUserW(user_token,
-                            command_line.c_str(),
+                            application_name.c_str(),
                             const_cast<LPWSTR>(command_line.c_str()),
                             NULL,
                             NULL,
                             FALSE,
                             0,
                             NULL,
                             NULL,
                             &startup_info,
                             &process_info)) {
     LOG_GETLASTERROR(ERROR) <<
         "Failed to launch a process with a user token";
     return false;
   }
 
   CloseHandle(process_info.hThread);
   process_out->set_handle(process_info.hProcess);
   return true;
 }
 
 } // namespace
 
 namespace remoting {
 
 WtsSessionProcessLauncher::WtsSessionProcessLauncher(
     WtsConsoleMonitor* monitor,
-    const FilePath& host_binary)
+    const FilePath& host_binary,
+    base::Thread* io_thread)
     : host_binary_(host_binary),
+      io_thread_(io_thread),
       monitor_(monitor),
       state_(StateDetached) {
   monitor_->AddWtsConsoleObserver(this);
 }
 
 WtsSessionProcessLauncher::~WtsSessionProcessLauncher() {
   DCHECK(state_ == StateDetached);
   DCHECK(!timer_.IsRunning());
   DCHECK(process_.handle() == NULL);
   DCHECK(process_watcher_.GetWatchedObject() == NULL);
+  DCHECK(chromoting_channel_.get() == NULL);
 
   monitor_->RemoveWtsConsoleObserver(this);
 }
 
 void WtsSessionProcessLauncher::LaunchProcess() {
   DCHECK(state_ == StateStarting);
   DCHECK(!timer_.IsRunning());
   DCHECK(process_.handle() == NULL);
   DCHECK(process_watcher_.GetWatchedObject() == NULL);
+  DCHECK(chromoting_channel_.get() == NULL);
 
-  // Try to launch the process and attach an object watcher to the returned
-  // handle so that we get notified when the process terminates.
   launch_time_ = base::Time::Now();
-  if (LaunchProcessAsUser(host_binary_, session_token_, &process_)) {
-    if (process_watcher_.StartWatching(process_.handle(), this)) {
-      state_ = StateAttached;
-      return;
-    } else {
-      LOG(ERROR) << "Failed to arm the process watcher.";
-      process_.Terminate(0);
-      process_.Close();
+
+  string16 channel_name;
+  ScopedHandle pipe;
+  if (CreatePipeForIpcChannel(this, &channel_name, &pipe)) {
+    // Wrap the pipe into an IPC channel.
+    chromoting_channel_.reset(new IPC::ChannelProxy(
+        IPC::ChannelHandle(pipe.Get()),
+        IPC::Channel::MODE_SERVER,
+        this,
+        io_thread_->message_loop_proxy().get()));
+
+    string16 command_line =
+        base::StringPrintf(ASCIIToUTF16(kHostProcessCommandLineFormat).c_str(),
+                           host_binary_.value().c_str(),
+                           channel_name.c_str());
+
+    // Try to launch the process and attach an object watcher to the returned
+    // handle so that we get notified when the process terminates.
+    if (LaunchProcessAsUser(host_binary_, command_line, session_token_,
+                            &process_)) {
+      if (process_watcher_.StartWatching(process_.handle(), this)) {
+        state_ = StateAttached;
+        return;
+      } else {
+        LOG(ERROR) << "Failed to arm the process watcher.";
+        process_.Terminate(0);
+        process_.Close();
+      }
     }
+
+    chromoting_channel_.reset();
   }
 
   // Something went wrong. Try to launch the host again later. The attempts rate
   // is limited by exponential backoff.
   launch_backoff_ = std::max(launch_backoff_ * 2,
                              TimeDelta::FromSeconds(kMinLaunchDelaySeconds));
   launch_backoff_ = std::min(launch_backoff_,
                              TimeDelta::FromSeconds(kMaxLaunchDelaySeconds));
   timer_.Start(FROM_HERE, launch_backoff_,
                this, &WtsSessionProcessLauncher::LaunchProcess);
 }
 
 void WtsSessionProcessLauncher::OnObjectSignaled(HANDLE object) {
   DCHECK(state_ == StateAttached);
   DCHECK(!timer_.IsRunning());
   DCHECK(process_.handle() != NULL);
   DCHECK(process_watcher_.GetWatchedObject() == NULL);
+  DCHECK(chromoting_channel_.get() != NULL);
 
   // The host process has been terminated for some reason. The handle can now be
   // closed.
   process_.Close();
+  chromoting_channel_.reset();
 
   // Expand the backoff interval if the process has died quickly or reset it if
   // it was up longer than the maximum backoff delay.
   base::TimeDelta delta = base::Time::Now() - launch_time_;
   if (delta < base::TimeDelta() ||
       delta >= base::TimeDelta::FromSeconds(kMaxLaunchDelaySeconds)) {
     launch_backoff_ = base::TimeDelta();
   } else {
     launch_backoff_ = std::max(launch_backoff_ * 2,
                                TimeDelta::FromSeconds(kMinLaunchDelaySeconds));
     launch_backoff_ = std::min(launch_backoff_,
                                TimeDelta::FromSeconds(kMaxLaunchDelaySeconds));
   }
 
   // Try to restart the host.
   state_ = StateStarting;
   timer_.Start(FROM_HERE, launch_backoff_,
                this, &WtsSessionProcessLauncher::LaunchProcess);
 }
 
+bool WtsSessionProcessLauncher::OnMessageReceived(const IPC::Message& message) {
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP(WtsSessionProcessLauncher, message)
+      IPC_MESSAGE_HANDLER(ChromotingHostMsg_SendSasToConsole,
+                          OnSendSasToConsole)
+      IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+  return handled;
+}
+
+void WtsSessionProcessLauncher::OnSendSasToConsole() {
+  if (state_ == StateAttached) {
+    if (sas_injector_.get() == NULL) {
+      sas_injector_ = SasInjector::Create();
+    }
+
+    if (sas_injector_.get() != NULL) {
+      sas_injector_->InjectSas();
+    }
+  }
+}
+
 void WtsSessionProcessLauncher::OnSessionAttached(uint32 session_id) {
   DCHECK(state_ == StateDetached);
   DCHECK(!timer_.IsRunning());
   DCHECK(process_.handle() == NULL);
   DCHECK(process_watcher_.GetWatchedObject() == NULL);
+  DCHECK(chromoting_channel_.get() == NULL);
 
   // Temporarily enable the SE_TCB_NAME privilege. The privileged token is
   // created as needed and kept for later reuse.
   if (privileged_token_.Get() == NULL) {
     if (!CreatePrivilegedToken(&privileged_token_)) {
       return;
     }
   }
 
   if (!ImpersonateLoggedOnUser(privileged_token_)) {
     LOG_GETLASTERROR(ERROR) <<
         "Failed to impersonate the privileged token";
     return;
   }
 
-  // While the SE_TCB_NAME progolege is enabled, create a session token for
+  // While the SE_TCB_NAME privilege is enabled, create a session token for
   // the launched process.
   bool result = CreateSessionToken(session_id, &session_token_);
 
   // Revert to the default token. The default token is sufficient to call
   // CreateProcessAsUser() successfully.
   CHECK(RevertToSelf());
 
   if (!result)
     return;
 
   // Now try to launch the host.
   state_ = StateStarting;
   LaunchProcess();
 }
 
 void WtsSessionProcessLauncher::OnSessionDetached() {
   DCHECK(state_ == StateDetached ||
          state_ == StateStarting ||
          state_ == StateAttached);
 
   switch (state_) {
     case StateDetached:
       DCHECK(!timer_.IsRunning());
       DCHECK(process_.handle() == NULL);
       DCHECK(process_watcher_.GetWatchedObject() == NULL);
+      DCHECK(chromoting_channel_.get() == NULL);
       break;
 
     case StateStarting:
       DCHECK(timer_.IsRunning());
       DCHECK(process_.handle() == NULL);
       DCHECK(process_watcher_.GetWatchedObject() == NULL);
+      DCHECK(chromoting_channel_.get() == NULL);
 
       timer_.Stop();
       launch_backoff_ = base::TimeDelta();
       state_ = StateDetached;
       break;
 
     case StateAttached:
       DCHECK(!timer_.IsRunning());
       DCHECK(process_.handle() != NULL);
       DCHECK(process_watcher_.GetWatchedObject() != NULL);
+      DCHECK(chromoting_channel_.get() != NULL);
 
       process_watcher_.StopWatching();
       process_.Terminate(0);
       process_.Close();
+      chromoting_channel_.reset();
       state_ = StateDetached;
       break;
   }
 }
 
 } // namespace remoting