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

remoting/host/sas_injector_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.
+
+#include "remoting/host/sas_injector.h"
+
+#include <windows.h>
+#include <string>
+
+#include "base/logging.h"
+#include "base/file_path.h"
+#include "base/native_library.h"
+#include "base/path_service.h"
+#include "base/utf_string_conversions.h"
+#include "base/win/registry.h"
+#include "base/win/windows_version.h"
+
+namespace remoting {
+
+namespace {
+
+// Names of the API and library implementing software SAS generation.
+const FilePath::CharType kSasDllFileName[] =
+    FILE_PATH_LITERAL("sas.dll");
+const char kSendSasName[] = "SendSAS";
+
+// The prototype of SendSAS().
+typedef VOID (WINAPI *SendSasFunc)(BOOL);
+
+// The registry key and value holding the policy controlling software SAS
+// generation.
+const char kSystemPolicyKeyName[] =
+    "Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System";
+const char kSoftwareSasValueName[] = "SoftwareSASGeneration";
+
+const DWORD kEnableSoftwareSasByServices = 1;
+
+// Toggles the default software SAS generation policy to enable SAS generation
+// by services. Non-default policy is not changed.
+class ScopedSoftwareSasPolicy {
+ public:
+  ScopedSoftwareSasPolicy();
+  ~ScopedSoftwareSasPolicy();
+
+  bool Apply();
+
+ private:
+  // The handle of the registry key were SoftwareSASGeneration policy is stored.
+  base::win::RegKey system_policy_;
+
+  // Name of the registry value holding the policy.
+  string16 value_name_;
+
+  // True if the policy needs to be restored.
+  bool restore_policy_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedSoftwareSasPolicy);
+};
+
+ScopedSoftwareSasPolicy::ScopedSoftwareSasPolicy()
+    : restore_policy_(false) {
+}
+
+ScopedSoftwareSasPolicy::~ScopedSoftwareSasPolicy() {
+  // Restore the default policy by deleting the value that we have set.
+  if (restore_policy_) {
+    LONG result = system_policy_.DeleteValue(value_name_.c_str());
+    if (result != ERROR_SUCCESS) {
+      SetLastError(result);
+      LOG_GETLASTERROR(ERROR)
+          << "Failed to restore the software SAS generation policy";
+    }
+  }
+}
+
+bool ScopedSoftwareSasPolicy::Apply() {
+  // Query the currently set SoftwareSASGeneration policy.
+  LONG result = system_policy_.Open(HKEY_LOCAL_MACHINE,
+                                    ASCIIToUTF16(kSystemPolicyKeyName).c_str(),
+                                    KEY_QUERY_VALUE | KEY_SET_VALUE |
+                                        KEY_WOW64_64KEY);
+  if (result != ERROR_SUCCESS) {
+    SetLastError(result);
+    LOG_GETLASTERROR(ERROR) << "Failed to open 'HKLM\\"
+                            << kSystemPolicyKeyName << "'";
+    return false;
+  }
+
+  value_name_ = ASCIIToUTF16(kSoftwareSasValueName);
+  bool custom_policy = system_policy_.HasValue(value_name_.c_str());
+
+  // Override the default policy (i.e. there is no value in the registry) only.
+  if (!custom_policy) {
+    result = system_policy_.WriteValue(value_name_.c_str(),
+                                       kEnableSoftwareSasByServices);
+    if (result != ERROR_SUCCESS) {
+      SetLastError(result);
+      LOG_GETLASTERROR(ERROR)
+          << "Failed to enable software SAS generation by services";
+      return false;
+    } else {
+      restore_policy_ = true;
+    }
+  }
+
+  return true;
+}
+
+} // namespace
+
+// Sends the Secure Attention Sequence using the SendSAS() function from
+// sas.dll. This library is shipped starting from Win7/W2K8 R2 only. However
+// Win7 SDK includes a redistributable verion of the same library that works on
+// Vista/W2K8. We install the latter along with our binaries.
+class SasInjectorWin : public SasInjector {
+ public:
+  SasInjectorWin();
+  virtual ~SasInjectorWin();
+
+  // SasInjector implementation.
+  virtual bool InjectSas() OVERRIDE;
+
+ private:
+  base::NativeLibrary sas_dll_;
+  SendSasFunc send_sas_;
+};
+
+SasInjectorWin::SasInjectorWin() : sas_dll_(NULL), send_sas_(NULL) {
+}
+
+SasInjectorWin::~SasInjectorWin() {
+  if (sas_dll_ != NULL) {
+    base::UnloadNativeLibrary(sas_dll_);
+  }
+}
+
+bool SasInjectorWin::InjectSas() {
+  // Load sas.dll. The library is expected to be in the same folder as this
+  // binary.
+  if (sas_dll_ == NULL) {
+    FilePath exe_path;
+    if (!PathService::Get(base::FILE_EXE, &exe_path)) {
+      LOG(ERROR) << "Failed to get the executable file name.";
+      return false;
+    }
+
+    std::string error;
+    sas_dll_ = base::LoadNativeLibrary(
+                   exe_path.DirName().Append(kSasDllFileName),
+                   &error);
+    if (sas_dll_ == NULL) {
+      LOG(ERROR) << "Failed to load '" << kSasDllFileName << "'";
+      return false;
+    }
+  }
+
+  // Get the pointer to sas!SendSAS().
+  if (send_sas_ == NULL) {
+    send_sas_ = reinterpret_cast<SendSasFunc>(
+      base::GetFunctionPointerFromNativeLibrary(sas_dll_, kSendSasName));
+    if (send_sas_ == NULL) {
+      LOG(ERROR) << "Failed to retrieve the address of '" << kSendSasName
+                 << "()'";
+      return false;
+    }
+  }
+
+  // Enable software SAS generation by services and send SAS. SAS can still fail
+  // if the policy does not allow services to generate software SAS.
+  ScopedSoftwareSasPolicy enable_sas;
+  if (!enable_sas.Apply())
+    return false;
+
+  (*send_sas_)(FALSE);
+  return true;
+}
+
+scoped_ptr<SasInjector> SasInjector::Create() {
+  if (base::win::OSInfo::GetInstance()->version() >= base::win::VERSION_VISTA) {
+    return scoped_ptr<SasInjector>(new SasInjectorWin());
+  }
+
+  return scoped_ptr<SasInjector>();
+}
+
+} // namespace remoting