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// Copyright 2012 The Chromium Authors
// 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 <memory>
#include <utility>
#include "base/files/file_path.h"
#include "base/logging.h"
#include "base/scoped_native_library.h"
#include "base/win/registry.h"
namespace remoting {
namespace {
// The registry key and value holding the policy controlling software SAS
// generation.
const wchar_t kSystemPolicyKeyName[] =
L"Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System";
const wchar_t kSoftwareSasValueName[] = L"SoftwareSASGeneration";
const DWORD kEnableSoftwareSasByServices = 1;
// https://docs.microsoft.com/en-us/windows/win32/api/sas/nf-sas-sendsas
typedef void(NTAPI* SendSASFunction)(BOOL);
// Toggles the default software SAS generation policy to enable SAS generation
// by services. Non-default policy is not changed.
class ScopedSoftwareSasPolicy {
public:
ScopedSoftwareSasPolicy();
ScopedSoftwareSasPolicy(const ScopedSoftwareSasPolicy&) = delete;
ScopedSoftwareSasPolicy& operator=(const ScopedSoftwareSasPolicy&) = delete;
~ScopedSoftwareSasPolicy();
bool Apply();
private:
// The handle of the registry key were SoftwareSASGeneration policy is stored.
base::win::RegKey system_policy_;
// True if the policy needs to be restored.
bool restore_policy_ = false;
};
ScopedSoftwareSasPolicy::ScopedSoftwareSasPolicy() = default;
ScopedSoftwareSasPolicy::~ScopedSoftwareSasPolicy() {
// Restore the default policy by deleting the value that we have set.
if (restore_policy_) {
LONG result = system_policy_.DeleteValue(kSoftwareSasValueName);
if (result != ERROR_SUCCESS) {
SetLastError(result);
PLOG(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, kSystemPolicyKeyName,
KEY_QUERY_VALUE | KEY_SET_VALUE | KEY_WOW64_64KEY);
if (result != ERROR_SUCCESS) {
SetLastError(result);
PLOG(ERROR) << "Failed to open 'HKLM\\" << kSystemPolicyKeyName << "'";
return false;
}
bool custom_policy = system_policy_.HasValue(kSoftwareSasValueName);
// Override the default policy (i.e. there is no value in the registry) only.
if (!custom_policy) {
result = system_policy_.WriteValue(kSoftwareSasValueName,
kEnableSoftwareSasByServices);
if (result != ERROR_SUCCESS) {
SetLastError(result);
PLOG(ERROR) << "Failed to enable software SAS generation by services";
return false;
} else {
restore_policy_ = true;
}
}
return true;
}
} // namespace
// Sends Secure Attention Sequence. Checks the current policy before sending.
class SasInjectorWin : public SasInjector {
public:
SasInjectorWin();
SasInjectorWin(const SasInjectorWin&) = delete;
SasInjectorWin& operator=(const SasInjectorWin&) = delete;
~SasInjectorWin() override;
// SasInjector implementation.
bool InjectSas() override;
};
SasInjectorWin::SasInjectorWin() = default;
SasInjectorWin::~SasInjectorWin() = default;
bool SasInjectorWin::InjectSas() {
// 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()) {
LOG(ERROR) << "SAS policy could not be applied, skipping SAS injection.";
return false;
}
// Use LoadLibrary here as sas.dll is not consistently shipped on all Windows
// SKUs (notably server releases) and linking against it prevents the host
// from starting correctly.
bool sas_injected = false;
base::ScopedNativeLibrary library(base::FilePath(L"sas.dll"));
if (library.is_valid()) {
SendSASFunction send_sas_func = reinterpret_cast<SendSASFunction>(
library.GetFunctionPointer("SendSAS"));
if (send_sas_func) {
sas_injected = true;
send_sas_func(/*AsUser=*/FALSE);
} else {
LOG(ERROR) << "SendSAS() not found in sas.dll, skipping SAS injection.";
}
} else {
LOG(ERROR) << "sas.dll could not be loaded, skipping SAS injection.";
}
return sas_injected;
}
std::unique_ptr<SasInjector> SasInjector::Create() {
return std::make_unique<SasInjectorWin>();
}
} // namespace remoting
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