139 lines
5.4 KiB
Plaintext
139 lines
5.4 KiB
Plaintext
// Copyright (c) 2016 Ryan Prichard
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to
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// deal in the Software without restriction, including without limitation the
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// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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// sell copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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// IN THE SOFTWARE.
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#include "GenRandom.h"
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#include <stdint.h>
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#include <string.h>
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#include "DebugClient.h"
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#include "StringBuilder.h"
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static volatile LONG g_pipeCounter;
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GenRandom::GenRandom() : m_advapi32(L"advapi32.dll") {
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// First try to use the pseudo-documented RtlGenRandom function from
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// advapi32.dll. Creating a CryptoAPI context is slow, and RtlGenRandom
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// avoids the overhead. It's documented in this blog post[1] and on
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// MSDN[2] with a disclaimer about future breakage. This technique is
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// apparently built-in into the MSVC CRT, though, for the rand_s function,
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// so perhaps it is stable enough.
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//
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// [1] http://blogs.msdn.com/b/michael_howard/archive/2005/01/14/353379.aspx
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// [2] https://msdn.microsoft.com/en-us/library/windows/desktop/aa387694(v=vs.85).aspx
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//
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// Both RtlGenRandom and the Crypto API functions exist in XP and up.
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m_rtlGenRandom = reinterpret_cast<RtlGenRandom_t*>(
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m_advapi32.proc("SystemFunction036"));
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// The OsModule class logs an error message if the proc is nullptr.
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if (m_rtlGenRandom != nullptr) {
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return;
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}
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// Fall back to the crypto API.
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m_cryptProvIsValid =
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CryptAcquireContext(&m_cryptProv, nullptr, nullptr,
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PROV_RSA_FULL, CRYPT_VERIFYCONTEXT) != 0;
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if (!m_cryptProvIsValid) {
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trace("GenRandom: CryptAcquireContext failed: %u",
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static_cast<unsigned>(GetLastError()));
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}
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}
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GenRandom::~GenRandom() {
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if (m_cryptProvIsValid) {
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CryptReleaseContext(m_cryptProv, 0);
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}
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}
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// Returns false if the context is invalid or the generation fails.
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bool GenRandom::fillBuffer(void *buffer, size_t size) {
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memset(buffer, 0, size);
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bool success = false;
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if (m_rtlGenRandom != nullptr) {
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success = m_rtlGenRandom(buffer, size) != 0;
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if (!success) {
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trace("GenRandom: RtlGenRandom/SystemFunction036 failed: %u",
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static_cast<unsigned>(GetLastError()));
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}
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} else if (m_cryptProvIsValid) {
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success =
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CryptGenRandom(m_cryptProv, size,
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reinterpret_cast<BYTE*>(buffer)) != 0;
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if (!success) {
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trace("GenRandom: CryptGenRandom failed, size=%d, lasterror=%u",
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static_cast<int>(size),
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static_cast<unsigned>(GetLastError()));
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}
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}
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return success;
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}
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// Returns an empty string if either of CryptAcquireContext or CryptGenRandom
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// fail.
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std::string GenRandom::randomBytes(size_t numBytes) {
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std::string ret(numBytes, '\0');
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if (!fillBuffer(&ret[0], numBytes)) {
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return std::string();
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}
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return ret;
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}
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std::wstring GenRandom::randomHexString(size_t numBytes) {
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const std::string bytes = randomBytes(numBytes);
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std::wstring ret(bytes.size() * 2, L'\0');
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for (size_t i = 0; i < bytes.size(); ++i) {
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static const wchar_t hex[] = L"0123456789abcdef";
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ret[i * 2] = hex[static_cast<uint8_t>(bytes[i]) >> 4];
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ret[i * 2 + 1] = hex[static_cast<uint8_t>(bytes[i]) & 0xF];
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}
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return ret;
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}
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// Returns a 64-bit value representing the number of 100-nanosecond intervals
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// since January 1, 1601.
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static uint64_t systemTimeAsUInt64() {
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FILETIME monotonicTime = {};
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GetSystemTimeAsFileTime(&monotonicTime);
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return (static_cast<uint64_t>(monotonicTime.dwHighDateTime) << 32) |
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static_cast<uint64_t>(monotonicTime.dwLowDateTime);
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}
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// Generates a unique and hard-to-guess case-insensitive string suitable for
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// use in a pipe filename or a Windows object name.
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std::wstring GenRandom::uniqueName() {
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// First include enough information to avoid collisions assuming
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// cooperative software. This code assumes that a process won't die and
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// be replaced with a recycled PID within a single GetSystemTimeAsFileTime
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// interval.
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WStringBuilder sb(64);
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sb << GetCurrentProcessId()
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<< L'-' << InterlockedIncrement(&g_pipeCounter)
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<< L'-' << whexOfInt(systemTimeAsUInt64());
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// It isn't clear to me how the crypto APIs would fail. It *probably*
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// doesn't matter that much anyway? In principle, a predictable pipe name
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// is subject to a local denial-of-service attack.
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auto random = randomHexString(16);
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if (!random.empty()) {
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sb << L'-' << random;
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}
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return sb.str_moved();
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}
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