Update safe_bcmp.c

main/safe_bcmp.c

@@ -1,44 +1,51 @@
 /*
-  +----------------------------------------------------------------------+
-  | 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:           |
-  | https://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]>                           |
-  +----------------------------------------------------------------------+
+   +----------------------------------------------------------------------+
+   | 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:           |
+   | https://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, non-zero if they don't.
- * Returns -1 early if inputs do not have the same lengths.
- *
+/**
+ * Constant-time binary comparison of two zend_strings.
+ * 
+ * @param a First string to compare
+ * @param b Second string to compare
+ * @return 0 if strings are identical, -1 if lengths differ, non-zero otherwise
+ * 
+ * @note This is security-sensitive code. Timing attacks are mitigated by:
+ *       - Using volatile to prevent compiler optimizations
+ *       - Constant-time comparison regardless of input
+ *       - Complete length comparison before content comparison
  */
 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;
+    const volatile unsigned char *ua = (const volatile unsigned char *)ZSTR_VAL(a);
+    const volatile unsigned char *ub = (const volatile unsigned char *)ZSTR_VAL(b);
+    const size_t len_a = ZSTR_LEN(a);
+    const size_t len_b = ZSTR_LEN(b);
+    int r = 0;
 
-	if (ZSTR_LEN(a) != ZSTR_LEN(b)) {
-		return -1;
-	}
+    // Early length check (safe as lengths are not secret)
+    if (len_a != len_b) {
+        return -1;
+    }
 
-	/* This is security sensitive code. Do not optimize this for speed. */
-	while (i < ZSTR_LEN(a)) {
-		r |= ua[i] ^ ub[i];
-		++i;
-	}
+    // Constant-time comparison
+    for (size_t i = 0; i < len_a; ++i) {
+        r |= ua[i] ^ ub[i];
+    }
 
-	return r;
+    return r;
 }