rufus/src/pki.c

/*
 * Rufus: The Reliable USB Formatting Utility
 * PKI functions (code signing, etc.)
 * Copyright © 2015 Pete Batard <pete@akeo.ie>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/* Memory leaks detection - define _CRTDBG_MAP_ALLOC as preprocessor macro */
#ifdef _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
#endif

#include <windows.h>
#include <stdio.h>
#include <wincrypt.h>
#include <wintrust.h>

#include "rufus.h"
#include "msapi_utf8.h"
#include "resource.h"
#include "localization.h"

#define ENCODING (X509_ASN_ENCODING | PKCS_7_ASN_ENCODING)

// Signatures names we accept (may be suffixed, but the signature should start with one of those)
const char* valid_cert_names[] = { "Akeo Consulting", "Akeo Systems", "Pete Batard" };

typedef struct {
	LPWSTR lpszProgramName;
	LPWSTR lpszPublisherLink;
	LPWSTR lpszMoreInfoLink;
} SPROG_PUBLISHERINFO, *PSPROG_PUBLISHERINFO;

// Mostly from https://support.microsoft.com/en-us/kb/323809
static char* GetSignatureName(const char* path)
{
	static char szSubjectName[128];
	char* p = NULL;
	BOOL r;
	HCERTSTORE hStore = NULL;
	HCRYPTMSG hMsg = NULL;
	PCCERT_CONTEXT pCertContext = NULL;
	DWORD dwEncoding, dwContentType, dwFormatType, dwSubjectSize;
	PCMSG_SIGNER_INFO pSignerInfo = NULL;
	PCMSG_SIGNER_INFO pCounterSignerInfo = NULL;
	DWORD dwSignerInfo = 0;
	CERT_INFO CertInfo = { 0 };
	SPROG_PUBLISHERINFO ProgPubInfo = { 0 };
	wchar_t *szFileName = utf8_to_wchar(path);

	// Get message handle and store handle from the signed file.
	r = CryptQueryObject(CERT_QUERY_OBJECT_FILE, szFileName,
		CERT_QUERY_CONTENT_FLAG_PKCS7_SIGNED_EMBED, CERT_QUERY_FORMAT_FLAG_BINARY,
		0, &dwEncoding, &dwContentType, &dwFormatType, &hStore, &hMsg, NULL);
	if (!r) {
		uprintf("PKI: Failed to get store handle for '%s': %s", path, WindowsErrorString());
		goto out;
	}

	// Get signer information size.
	r = CryptMsgGetParam(hMsg, CMSG_SIGNER_INFO_PARAM, 0, NULL, &dwSignerInfo);
	if (!r) {
		uprintf("PKI: Failed to get signer size: %s", WindowsErrorString);
		goto out;
	}

	// Allocate memory for signer information.
	pSignerInfo = (PCMSG_SIGNER_INFO)calloc(dwSignerInfo, 1);
	if (!pSignerInfo) {
		uprintf("PKI: Could not allocate memory for signer information");
		goto out;
	}

	// Get Signer Information.
	r = CryptMsgGetParam(hMsg, CMSG_SIGNER_INFO_PARAM, 0, (PVOID)pSignerInfo, &dwSignerInfo);
	if (!r) {
		uprintf("PKI: Failed to get signer information: %s", WindowsErrorString());
		goto out;
	}

	// Search for the signer certificate in the temporary certificate store.
	CertInfo.Issuer = pSignerInfo->Issuer;
	CertInfo.SerialNumber = pSignerInfo->SerialNumber;

	pCertContext = CertFindCertificateInStore(hStore, ENCODING, 0, CERT_FIND_SUBJECT_CERT, (PVOID)&CertInfo, NULL);
	if (!pCertContext) {
		uprintf("PKI: Failed to locate signer certificate in temporary store: %s", WindowsErrorString());
		goto out;
	}

	// Isolate the signing certificate subject name
	dwSubjectSize = CertGetNameStringA(pCertContext, CERT_NAME_SIMPLE_DISPLAY_TYPE, 0, NULL,
		szSubjectName, sizeof(szSubjectName));
	if (dwSubjectSize <= 1) {
		uprintf("PKI: Failed to get Subject Name");
		goto out;
	}

	uprintf("Downloaded executable is signed by '%s'", szSubjectName);
	p = szSubjectName;

out:
	safe_free(szFileName);
	safe_free(ProgPubInfo.lpszProgramName);
	safe_free(ProgPubInfo.lpszPublisherLink);
	safe_free(ProgPubInfo.lpszMoreInfoLink);
	safe_free(pSignerInfo);
	safe_free(pCounterSignerInfo);
	if (pCertContext != NULL)
		CertFreeCertificateContext(pCertContext);
	if (hStore != NULL)
		CertCloseStore(hStore, 0);
	if (hMsg != NULL)
		CryptMsgClose(hMsg);
	return p;
}

// From https://msdn.microsoft.com/en-us/library/windows/desktop/aa382384.aspx
LONG ValidateSignature(HWND hDlg, const char* path)
{
	LONG r;
	WINTRUST_DATA trust_data = { 0 };
	WINTRUST_FILE_INFO trust_file = { 0 };
	GUID guid_generic_verify =	// WINTRUST_ACTION_GENERIC_VERIFY_V2
		{ 0xaac56b, 0xcd44, 0x11d0,{ 0x8c, 0xc2, 0x0, 0xc0, 0x4f, 0xc2, 0x95, 0xee } };
	char *signature_name;
	size_t i, len;

	// Check the signature name. Make it specific enough (i.e. don't simply check for "Akeo")
	// so that, besides hacking our server, it'll place an extra hurdle on any malicious entity
	// into also fooling a C.A. to issue a certificate that passes our test.
	signature_name = GetSignatureName(path);
	if (signature_name == NULL) {
		uprintf("PKI: Could not get signature name");
		MessageBoxExU(hDlg, lmprintf(MSG_284), lmprintf(MSG_283), MB_OK | MB_ICONERROR | MB_IS_RTL, selected_langid);
		return TRUST_E_NOSIGNATURE;
	}
	for (i = 0; i < ARRAYSIZE(valid_cert_names); i++) {
		len = strlen(valid_cert_names[i]);
		if (strncmp(signature_name, valid_cert_names[i], len) == 0) {
			// Test for whitespace after the part we match, for added safety
			if ((len >= strlen(signature_name)) || isspace(signature_name[len]))
				break;
		}
	}
	if (i >= ARRAYSIZE(valid_cert_names)) {
		uprintf("PKI: Signature '%s' is unexpected...", signature_name);
		if (MessageBoxExU(hDlg, lmprintf(MSG_285, signature_name), lmprintf(MSG_283),
			MB_YESNO | MB_ICONWARNING | MB_IS_RTL, selected_langid) != IDYES)
			return TRUST_E_EXPLICIT_DISTRUST;
	}

	trust_file.cbStruct = sizeof(trust_file);
	trust_file.pcwszFilePath = utf8_to_wchar(path);
	if (trust_file.pcwszFilePath == NULL) {
		uprintf("PKI: Unable to convert '%s' to UTF16", path);
		return ERROR_SEVERITY_ERROR | FAC(FACILITY_CERT) | ERROR_NOT_ENOUGH_MEMORY;
	}

	trust_data.cbStruct = sizeof(trust_data);
	trust_data.dwUIChoice = WTD_UI_ALL;
	// We just downloaded from the Internet, so we should be able to check revocation
	trust_data.fdwRevocationChecks = WTD_REVOKE_WHOLECHAIN;
	// 0x400 = WTD_MOTW  for Windows 8.1 or later
	trust_data.dwProvFlags = WTD_REVOCATION_CHECK_CHAIN | 0x400;
	trust_data.dwUnionChoice = WTD_CHOICE_FILE;
	trust_data.pFile = &trust_file;

	r = WinVerifyTrust(NULL, &guid_generic_verify, &trust_data);
	safe_free(trust_file.pcwszFilePath);

	return r;
}