Rewrite BCryptGenRandom and add tests

dll/bcrypt.cpp

@@ -1,21 +1,64 @@
 #include "common.h"
 
-#include <algorithm>
-#include <climits>
-#include <random>
+#include <sys/random.h>
+#include <vector>
+
+namespace {
 
 typedef PVOID BCRYPT_ALG_HANDLE;
 
-namespace bcrypt {
+constexpr ULONG BCRYPT_RNG_USE_ENTROPY_IN_BUFFER = 0x00000001;
+constexpr ULONG BCRYPT_USE_SYSTEM_PREFERRED_RNG = 0x00000002;
 
-using random_bytes_engine = std::independent_bits_engine<std::default_random_engine, CHAR_BIT, unsigned char>;
+bool fillWithSystemRandom(PUCHAR buffer, size_t length) {
+	while (length > 0) {
+		ssize_t written = getrandom(buffer, length, 0);
+		if (written < 0) {
+			if (errno == EINTR)
+				continue;
+			return false;
+		}
+		if (written == 0)
+			continue;
+		buffer += written;
+		length -= static_cast<size_t>(written);
+	}
+	return true;
+}
+
+} // namespace
+
+namespace bcrypt {
 
 NTSTATUS WIN_FUNC BCryptGenRandom(BCRYPT_ALG_HANDLE hAlgorithm, PUCHAR pbBuffer, ULONG cbBuffer, ULONG dwFlags) {
 	DEBUG_LOG("BCryptGenRandom(%p, %p, %lu, %lu)\n", hAlgorithm, pbBuffer, cbBuffer, dwFlags);
-	assert(hAlgorithm == nullptr);
-	assert(dwFlags == 0 || dwFlags == 2 /* BCRYPT_USE_SYSTEM_PREFERRED_RNG */);
-	random_bytes_engine rbe;
-	std::generate(pbBuffer, pbBuffer + cbBuffer, std::ref(rbe));
+	if (pbBuffer == nullptr && cbBuffer != 0)
+		return STATUS_INVALID_HANDLE;
+
+	if (hAlgorithm != nullptr)
+		return STATUS_NOT_IMPLEMENTED;
+
+	if ((dwFlags & BCRYPT_USE_SYSTEM_PREFERRED_RNG) == 0)
+		return STATUS_INVALID_HANDLE;
+
+	ULONG allowedFlags = BCRYPT_RNG_USE_ENTROPY_IN_BUFFER | BCRYPT_USE_SYSTEM_PREFERRED_RNG;
+	if ((dwFlags & ~allowedFlags) != 0)
+		return STATUS_INVALID_PARAMETER;
+
+	if (cbBuffer == 0)
+		return STATUS_SUCCESS;
+
+	std::vector<unsigned char> entropy;
+	if ((dwFlags & BCRYPT_RNG_USE_ENTROPY_IN_BUFFER) && pbBuffer != nullptr)
+		entropy.assign(pbBuffer, pbBuffer + cbBuffer);
+
+	if (!fillWithSystemRandom(pbBuffer, cbBuffer))
+		return STATUS_UNEXPECTED_IO_ERROR;
+
+	if (!entropy.empty()) {
+		for (size_t i = 0; i < entropy.size(); ++i)
+			pbBuffer[i] ^= entropy[i];
+	}
 	return STATUS_SUCCESS;
 }