remoting/host/win/unprivileged_process_delegate.cc

   1
   2 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   3 // Use of this source code is governed by a BSD-style license that can be
   4 // found in the LICENSE file.
   5 //
   6 // This file implements the Windows service controlling Me2Me host processes
   7 // running within user sessions.
   8
   9 #include "remoting/host/win/unprivileged_process_delegate.h"
  10
  11 #include <sddl.h>
  12
  13 #include "base/command_line.h"
  14 #include "base/files/file.h"
  15 #include "base/logging.h"
  16 #include "base/rand_util.h"
  17 #include "base/single_thread_task_runner.h"
  18 #include "base/strings/string16.h"
  19 #include "base/strings/stringprintf.h"
  20 #include "base/strings/utf_string_conversions.h"
  21 #include "base/synchronization/lock.h"
  22 #include "base/win/scoped_handle.h"
  23 #include "base/win/windows_version.h"
  24 #include "ipc/ipc_channel.h"
  25 #include "ipc/ipc_channel_proxy.h"
  26 #include "ipc/ipc_message.h"
  27 #include "remoting/base/typed_buffer.h"
  28 #include "remoting/host/ipc_util.h"
  29 #include "remoting/host/switches.h"
  30 #include "remoting/host/win/launch_process_with_token.h"
  31 #include "remoting/host/win/security_descriptor.h"
  32 #include "remoting/host/win/window_station_and_desktop.h"
  33 #include "sandbox/win/src/restricted_token.h"
  34
  35 using base::win::ScopedHandle;
  36
  37 namespace remoting {
  38
  39 namespace {
  40
  41 // The security descriptors below are used to lock down access to the worker
  42 // process launched by UnprivilegedProcessDelegate. UnprivilegedProcessDelegate
  43 // assumes that it runs under SYSTEM. The worker process is launched under
  44 // a different account and attaches to a newly created window station. If UAC is
  45 // supported by the OS, the worker process is started at low integrity level.
  46 // UnprivilegedProcessDelegate replaces the first printf parameter in
  47 // the strings below by the logon SID assigned to the worker process.
  48
  49 // Security descriptor of the desktop the worker process attaches to. It gives
  50 // SYSTEM and the logon SID full access to the desktop.
  51 const char kDesktopSdFormat[] = "O:SYG:SYD:(A;;0xf01ff;;;SY)(A;;0xf01ff;;;%s)";
  52
  53 // Mandatory label specifying low integrity level.
  54 const char kLowIntegrityMandatoryLabel[] = "S:(ML;CIOI;NW;;;LW)";
  55
  56 // Security descriptor of the window station the worker process attaches to. It
  57 // gives SYSTEM and the logon SID full access the window station. The child
  58 // containers and objects inherit ACE giving SYSTEM and the logon SID full
  59 // access to them as well.
  60 const char kWindowStationSdFormat[] = "O:SYG:SYD:(A;CIOIIO;GA;;;SY)"
  61     "(A;CIOIIO;GA;;;%s)(A;NP;0xf037f;;;SY)(A;NP;0xf037f;;;%s)";
  62
  63 // Security descriptor of the worker process. It gives access SYSTEM full access
  64 // to the process. It gives READ_CONTROL, SYNCHRONIZE, PROCESS_QUERY_INFORMATION
  65 // and PROCESS_TERMINATE rights to the built-in administrators group.
  66 const char kWorkerProcessSd[] = "O:SYG:SYD:(A;;GA;;;SY)(A;;0x120401;;;BA)";
  67
  68 // Security descriptor of the worker process threads. It gives access SYSTEM
  69 // full access to the threads. It gives READ_CONTROL, SYNCHRONIZE,
  70 // THREAD_QUERY_INFORMATION and THREAD_TERMINATE rights to the built-in
  71 // administrators group.
  72 const char kWorkerThreadSd[] = "O:SYG:SYD:(A;;GA;;;SY)(A;;0x120801;;;BA)";
  73
  74 // Creates a token with limited access that will be used to run the worker
  75 // process.
  76 bool CreateRestrictedToken(ScopedHandle* token_out) {
  77   // Create a token representing LocalService account.
  78   HANDLE temp_handle;
  79   if (!LogonUser(L"LocalService", L"NT AUTHORITY", nullptr,
  80                  LOGON32_LOGON_SERVICE, LOGON32_PROVIDER_DEFAULT,
  81                  &temp_handle)) {
  82     return false;
  83   }
  84   ScopedHandle token(temp_handle);
  85
  86   sandbox::RestrictedToken restricted_token;
  87   if (restricted_token.Init(token.Get()) != ERROR_SUCCESS)
  88     return false;
  89
  90   // Remove all privileges in the token.
  91   if (restricted_token.DeleteAllPrivileges(nullptr) != ERROR_SUCCESS)
  92     return false;
  93
  94   // Set low integrity level if supported by the OS.
  95   if (base::win::GetVersion() >= base::win::VERSION_VISTA) {
  96     if (restricted_token.SetIntegrityLevel(sandbox::INTEGRITY_LEVEL_LOW)
  97         != ERROR_SUCCESS) {
  98       return false;
  99     }
 100   }
 101
 102   // Return the resulting token.
 103   if (restricted_token.GetRestrictedToken(token_out) ==  ERROR_SUCCESS)
 104     return true;
 105
 106   return false;
 107 }
 108
 109 // Creates a window station with a given name and the default desktop giving
 110 // the complete access to |logon_sid|.
 111 bool CreateWindowStationAndDesktop(ScopedSid logon_sid,
 112                                    WindowStationAndDesktop* handles_out) {
 113   // Convert the logon SID into a string.
 114   std::string logon_sid_string = ConvertSidToString(logon_sid.get());
 115   if (logon_sid_string.empty()) {
 116     PLOG(ERROR) << "Failed to convert a SID to string";
 117     return false;
 118   }
 119
 120   // Format the security descriptors in SDDL form.
 121   std::string desktop_sddl =
 122       base::StringPrintf(kDesktopSdFormat, logon_sid_string.c_str());
 123   std::string window_station_sddl =
 124       base::StringPrintf(kWindowStationSdFormat, logon_sid_string.c_str(),
 125                          logon_sid_string.c_str());
 126
 127   // The worker runs at low integrity level. Make sure it will be able to attach
 128   // to the window station and desktop.
 129   if (base::win::GetVersion() >= base::win::VERSION_VISTA) {
 130     desktop_sddl += kLowIntegrityMandatoryLabel;
 131     window_station_sddl += kLowIntegrityMandatoryLabel;
 132   }
 133
 134   // Create the desktop and window station security descriptors.
 135   ScopedSd desktop_sd = ConvertSddlToSd(desktop_sddl);
 136   ScopedSd window_station_sd = ConvertSddlToSd(window_station_sddl);
 137   if (!desktop_sd || !window_station_sd) {
 138     PLOG(ERROR) << "Failed to create a security descriptor.";
 139     return false;
 140   }
 141
 142   // GetProcessWindowStation() returns the current handle which does not need to
 143   // be freed.
 144   HWINSTA current_window_station = GetProcessWindowStation();
 145
 146   // Generate a unique window station name.
 147   std::string window_station_name = base::StringPrintf(
 148       "chromoting-%d-%d",
 149       base::GetCurrentProcId(),
 150       base::RandInt(1, std::numeric_limits<int>::max()));
 151
 152   // Make sure that a new window station will be created instead of opening
 153   // an existing one.
 154   DWORD window_station_flags = 0;
 155   if (base::win::GetVersion() >= base::win::VERSION_VISTA)
 156     window_station_flags = CWF_CREATE_ONLY;
 157
 158   // Request full access because this handle will be inherited by the worker
 159   // process which needs full access in order to attach to the window station.
 160   DWORD desired_access =
 161       WINSTA_ALL_ACCESS | DELETE | READ_CONTROL | WRITE_DAC | WRITE_OWNER;
 162
 163   SECURITY_ATTRIBUTES security_attributes = {0};
 164   security_attributes.nLength = sizeof(security_attributes);
 165   security_attributes.lpSecurityDescriptor = window_station_sd.get();
 166   security_attributes.bInheritHandle = TRUE;
 167
 168   WindowStationAndDesktop handles;
 169   handles.SetWindowStation(CreateWindowStation(
 170       base::UTF8ToUTF16(window_station_name).c_str(), window_station_flags,
 171       desired_access, &security_attributes));
 172   if (!handles.window_station()) {
 173     PLOG(ERROR) << "CreateWindowStation() failed";
 174     return false;
 175   }
 176
 177   // Switch to the new window station and create a desktop on it.
 178   if (!SetProcessWindowStation(handles.window_station())) {
 179     PLOG(ERROR) << "SetProcessWindowStation() failed";
 180     return false;
 181   }
 182
 183   desired_access = DESKTOP_READOBJECTS | DESKTOP_CREATEWINDOW |
 184       DESKTOP_CREATEMENU | DESKTOP_HOOKCONTROL | DESKTOP_JOURNALRECORD |
 185       DESKTOP_JOURNALPLAYBACK | DESKTOP_ENUMERATE | DESKTOP_WRITEOBJECTS |
 186       DESKTOP_SWITCHDESKTOP | DELETE | READ_CONTROL | WRITE_DAC | WRITE_OWNER;
 187
 188   security_attributes.nLength = sizeof(security_attributes);
 189   security_attributes.lpSecurityDescriptor = desktop_sd.get();
 190   security_attributes.bInheritHandle = TRUE;
 191
 192   // The default desktop of the interactive window station is called "Default".
 193   // Name the created desktop the same way in case any code relies on that.
 194   // The desktop name should not make any difference though.
 195   handles.SetDesktop(CreateDesktop(L"Default", nullptr, nullptr, 0,
 196                                    desired_access, &security_attributes));
 197
 198   // Switch back to the original window station.
 199   if (!SetProcessWindowStation(current_window_station)) {
 200     PLOG(ERROR) << "SetProcessWindowStation() failed";
 201     return false;
 202   }
 203
 204   if (!handles.desktop()) {
 205     PLOG(ERROR) << "CreateDesktop() failed";
 206     return false;
 207   }
 208
 209   handles.Swap(*handles_out);
 210   return true;
 211 }
 212
 213 }  // namespace
 214
 215 UnprivilegedProcessDelegate::UnprivilegedProcessDelegate(
 216     scoped_refptr<base::SingleThreadTaskRunner> io_task_runner,
 217     scoped_ptr<base::CommandLine> target_command)
 218     : io_task_runner_(io_task_runner),
 219       target_command_(target_command.Pass()),
 220       event_handler_(nullptr) {
 221 }
 222
 223 UnprivilegedProcessDelegate::~UnprivilegedProcessDelegate() {
 224   DCHECK(CalledOnValidThread());
 225   DCHECK(!channel_);
 226   DCHECK(!worker_process_.IsValid());
 227 }
 228
 229 void UnprivilegedProcessDelegate::LaunchProcess(
 230     WorkerProcessLauncher* event_handler) {
 231   DCHECK(CalledOnValidThread());
 232   DCHECK(!event_handler_);
 233
 234   event_handler_ = event_handler;
 235
 236   scoped_ptr<IPC::ChannelProxy> server;
 237
 238   // Create a restricted token that will be used to run the worker process.
 239   ScopedHandle token;
 240   if (!CreateRestrictedToken(&token)) {
 241     PLOG(ERROR) << "Failed to create a restricted LocalService token";
 242     ReportFatalError();
 243     return;
 244   }
 245
 246   // Determine our logon SID, so we can grant it access to our window station
 247   // and desktop.
 248   ScopedSid logon_sid = GetLogonSid(token.Get());
 249   if (!logon_sid) {
 250     PLOG(ERROR) << "Failed to retrieve the logon SID";
 251     ReportFatalError();
 252     return;
 253   }
 254
 255   // Create the process and thread security descriptors.
 256   ScopedSd process_sd = ConvertSddlToSd(kWorkerProcessSd);
 257   ScopedSd thread_sd = ConvertSddlToSd(kWorkerThreadSd);
 258   if (!process_sd || !thread_sd) {
 259     PLOG(ERROR) << "Failed to create a security descriptor";
 260     ReportFatalError();
 261     return;
 262   }
 263
 264   SECURITY_ATTRIBUTES process_attributes;
 265   process_attributes.nLength = sizeof(process_attributes);
 266   process_attributes.lpSecurityDescriptor = process_sd.get();
 267   process_attributes.bInheritHandle = FALSE;
 268
 269   SECURITY_ATTRIBUTES thread_attributes;
 270   thread_attributes.nLength = sizeof(thread_attributes);
 271   thread_attributes.lpSecurityDescriptor = thread_sd.get();
 272   thread_attributes.bInheritHandle = FALSE;
 273
 274   ScopedHandle worker_process;
 275   {
 276     // Take a lock why any inheritable handles are open to make sure that only
 277     // one process inherits them.
 278     base::AutoLock lock(g_inherit_handles_lock.Get());
 279
 280     // Create a connected IPC channel.
 281     base::File client;
 282     if (!CreateConnectedIpcChannel(io_task_runner_, this, &client, &server)) {
 283       ReportFatalError();
 284       return;
 285     }
 286
 287     // Convert the handle value into a decimal integer. Handle values are 32bit
 288     // even on 64bit platforms.
 289     std::string pipe_handle = base::StringPrintf(
 290         "%d", reinterpret_cast<ULONG_PTR>(client.GetPlatformFile()));
 291
 292     // Pass the IPC channel via the command line.
 293     base::CommandLine command_line(target_command_->argv());
 294     command_line.AppendSwitchASCII(kDaemonPipeSwitchName, pipe_handle);
 295
 296     // Create our own window station and desktop accessible by |logon_sid|.
 297     WindowStationAndDesktop handles;
 298     if (!CreateWindowStationAndDesktop(logon_sid.Pass(), &handles)) {
 299       PLOG(ERROR) << "Failed to create a window station and desktop";
 300       ReportFatalError();
 301       return;
 302     }
 303
 304     // Try to launch the worker process. The launched process inherits
 305     // the window station, desktop and pipe handles, created above.
 306     ScopedHandle worker_thread;
 307     if (!LaunchProcessWithToken(command_line.GetProgram(),
 308                                 command_line.GetCommandLineString(),
 309                                 token.Get(),
 310                                 &process_attributes,
 311                                 &thread_attributes,
 312                                 true,
 313                                 0,
 314                                 nullptr,
 315                                 &worker_process,
 316                                 &worker_thread)) {
 317       ReportFatalError();
 318       return;
 319     }
 320   }
 321
 322   channel_ = server.Pass();
 323   ReportProcessLaunched(worker_process.Pass());
 324 }
 325
 326 void UnprivilegedProcessDelegate::Send(IPC::Message* message) {
 327   DCHECK(CalledOnValidThread());
 328
 329   if (channel_) {
 330     channel_->Send(message);
 331   } else {
 332     delete message;
 333   }
 334 }
 335
 336 void UnprivilegedProcessDelegate::CloseChannel() {
 337   DCHECK(CalledOnValidThread());
 338
 339   channel_.reset();
 340 }
 341
 342 void UnprivilegedProcessDelegate::KillProcess() {
 343   DCHECK(CalledOnValidThread());
 344
 345   channel_.reset();
 346   event_handler_ = nullptr;
 347
 348   if (worker_process_.IsValid()) {
 349     TerminateProcess(worker_process_.Get(), CONTROL_C_EXIT);
 350     worker_process_.Close();
 351   }
 352 }
 353
 354 bool UnprivilegedProcessDelegate::OnMessageReceived(
 355     const IPC::Message& message) {
 356   DCHECK(CalledOnValidThread());
 357
 358   return event_handler_->OnMessageReceived(message);
 359 }
 360
 361 void UnprivilegedProcessDelegate::OnChannelConnected(int32 peer_pid) {
 362   DCHECK(CalledOnValidThread());
 363
 364   DWORD pid = GetProcessId(worker_process_.Get());
 365   if (pid != static_cast<DWORD>(peer_pid)) {
 366     LOG(ERROR) << "The actual client PID " << pid
 367                << " does not match the one reported by the client: "
 368                << peer_pid;
 369     ReportFatalError();
 370     return;
 371   }
 372
 373   event_handler_->OnChannelConnected(peer_pid);
 374 }
 375
 376 void UnprivilegedProcessDelegate::OnChannelError() {
 377   DCHECK(CalledOnValidThread());
 378
 379   event_handler_->OnChannelError();
 380 }
 381
 382 void UnprivilegedProcessDelegate::ReportFatalError() {
 383   DCHECK(CalledOnValidThread());
 384
 385   channel_.reset();
 386
 387   WorkerProcessLauncher* event_handler = event_handler_;
 388   event_handler_ = nullptr;
 389   event_handler->OnFatalError();
 390 }
 391
 392 void UnprivilegedProcessDelegate::ReportProcessLaunched(
 393     base::win::ScopedHandle worker_process) {
 394   DCHECK(CalledOnValidThread());
 395   DCHECK(!worker_process_.IsValid());
 396
 397   worker_process_ = worker_process.Pass();
 398
 399   // Report a handle that can be used to wait for the worker process completion,
 400   // query information about the process and duplicate handles.
 401   DWORD desired_access =
 402       SYNCHRONIZE | PROCESS_DUP_HANDLE | PROCESS_QUERY_INFORMATION;
 403   HANDLE temp_handle;
 404   if (!DuplicateHandle(GetCurrentProcess(),
 405                        worker_process_.Get(),
 406                        GetCurrentProcess(),
 407                        &temp_handle,
 408                        desired_access,
 409                        FALSE,
 410                        0)) {
 411     PLOG(ERROR) << "Failed to duplicate a handle";
 412     ReportFatalError();
 413     return;
 414   }
 415   ScopedHandle limited_handle(temp_handle);
 416
 417   event_handler_->OnProcessLaunched(limited_handle.Pass());
 418 }
 419
 420 }  // namespace remoting