Introduction of timing attack safe bcmp implementation.

Nothing new but to refactor usage b/w hash and password
extensions but using volatile pointers to be a bit safer,
allowing to expand its usage eventually.

Author: devnexen

configure.ac

@@ -1616,7 +1616,7 @@ PHP_ADD_SOURCES(main, main.c snprintf.c spprintf.c \
        php_ini_builder.c \
        php_ini.c SAPI.c rfc1867.c php_content_types.c strlcpy.c \
        strlcat.c explicit_bzero.c reentrancy.c php_variables.c php_ticks.c \
-       network.c php_open_temporary_file.c php_odbc_utils.c \
+       network.c php_open_temporary_file.c php_odbc_utils.c safe_bcmp.c \
        output.c getopt.c php_syslog.c, -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1)
 
 PHP_ADD_SOURCES_X(main, fastcgi.c, -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1, PHP_FASTCGI_OBJS, no)

ext/hash/hash.c

@@ -1111,9 +1111,7 @@ PHP_FUNCTION(hash_pbkdf2)
 PHP_FUNCTION(hash_equals)
 {
 	zval *known_zval, *user_zval;
-	char *known_str, *user_str;
 	int result = 0;
-	size_t j;
 
 	if (zend_parse_parameters(ZEND_NUM_ARGS(), "zz", &known_zval, &user_zval) == FAILURE) {
 		RETURN_THROWS();
@@ -1130,17 +1128,8 @@ PHP_FUNCTION(hash_equals)
 		RETURN_THROWS();
 	}
 
-	if (Z_STRLEN_P(known_zval) != Z_STRLEN_P(user_zval)) {
-		RETURN_FALSE;
-	}
-
-	known_str = Z_STRVAL_P(known_zval);
-	user_str = Z_STRVAL_P(user_zval);
-
 	/* This is security sensitive code. Do not optimize this for speed. */
-	for (j = 0; j < Z_STRLEN_P(known_zval); j++) {
-		result |= known_str[j] ^ user_str[j];
-	}
+	result = php_safe_bcmp(Z_STR_P(known_zval), Z_STR_P(user_zval));
 
 	RETURN_BOOL(0 == result);
 }

ext/standard/password.c

@@ -152,15 +152,14 @@ static bool php_password_bcrypt_needs_rehash(const zend_string *hash, zend_array
 }
 
 static bool php_password_bcrypt_verify(const zend_string *password, const zend_string *hash) {
-	size_t i;
 	int status = 0;
 	zend_string *ret = php_crypt(ZSTR_VAL(password), (int)ZSTR_LEN(password), ZSTR_VAL(hash), (int)ZSTR_LEN(hash), 1);
 
 	if (!ret) {
 		return 0;
 	}
 
-	if (ZSTR_LEN(ret) != ZSTR_LEN(hash) || ZSTR_LEN(hash) < 13) {
+	if (ZSTR_LEN(hash) < 13) {
 		zend_string_free(ret);
 		return 0;
 	}
@@ -169,9 +168,7 @@ static bool php_password_bcrypt_verify(const zend_string *password, const zend_s
 	 * resistance towards timing attacks. This is a constant time
 	 * equality check that will always check every byte of both
 	 * values. */
-	for (i = 0; i < ZSTR_LEN(hash); i++) {
-		status |= (ZSTR_VAL(ret)[i] ^ ZSTR_VAL(hash)[i]);
-	}
+	status = php_safe_bcmp(ret, hash);
 
 	zend_string_free(ret);
 	return status == 0;

main/php.h

@@ -179,6 +179,10 @@ END_EXTERN_C()
 #define explicit_bzero php_explicit_bzero
 #endif
 
+BEGIN_EXTERN_C()
+PHPAPI int php_safe_bcmp(const zend_string *a, const zend_string *b);
+END_EXTERN_C()
+
 #ifndef HAVE_STRTOK_R
 BEGIN_EXTERN_C()
 char *strtok_r(char *s, const char *delim, char **last);

main/safe_bcmp.c

@@ -0,0 +1,43 @@
+/*
+  +----------------------------------------------------------------------+
+  | Copyright (c) The PHP Group                                          |
+  +----------------------------------------------------------------------+
+  | This source file is subject to version 3.01 of the PHP license,      |
+  | that is bundled with this package in the file LICENSE, and is        |
+  | available through the world-wide-web at the following url:           |
+  | http://www.php.net/license/3_01.txt                                  |
+  | If you did not receive a copy of the PHP license and are unable to   |
+  | obtain it through the world-wide-web, please send a note to          |
+  | [email protected] so we can mail you a copy immediately.               |
+  +----------------------------------------------------------------------+
+  | Author: David Carlier <[email protected]>                           |
+  +----------------------------------------------------------------------+
+*/
+
+#include "php.h"
+
+#include <string.h>
+
+/*
+ * Returns 0 if both inputs match, 1 if they don't.
+ * Returns -1 early if inputs do not have the same lengths.
+ *
+ */
+PHPAPI int php_safe_bcmp(const zend_string *a, const zend_string *b)
+{
+	const volatile unsigned char *ua = (const volatile unsigned char *)ZSTR_VAL(a);
+	const volatile unsigned char *ub = (const volatile unsigned char *)ZSTR_VAL(b);
+	size_t i = 0;
+	int r = 0;
+
+	if (ZSTR_LEN(a) != ZSTR_LEN(b)) {
+		return -1;
+	}
+
+	while (i < ZSTR_LEN(a)) {
+		r |= ua[i] ^ ub[i];
+		++i;
+	}
+
+	return r;
+}

win32/build/config.w32

@@ -265,7 +265,7 @@ ADD_SOURCES("main", "main.c snprintf.c spprintf.c getopt.c fopen_wrappers.c \
 	php_scandir.c php_ini.c SAPI.c rfc1867.c php_content_types.c strlcpy.c \
 	strlcat.c reentrancy.c php_variables.c php_ticks.c network.c \
 	php_open_temporary_file.c output.c internal_functions.c \
-	php_syslog.c php_odbc_utils.c");
+	php_syslog.c php_odbc_utils.c safe_bcmp.c");
 ADD_FLAG("CFLAGS_BD_MAIN", "/D ZEND_ENABLE_STATIC_TSRMLS_CACHE=1");
 if (VS_TOOLSET && VCVERS >= 1914) {
 	ADD_FLAG("CFLAGS_BD_MAIN", "/d2FuncCache1");