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hash_equals: Don't leak length difference. (Bug 67939) #791

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hash_equals: Don't leak length difference. (Bug 67939) #791

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20 changes: 11 additions & 9 deletions ext/hash/hash.c
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Original file line number Diff line number Diff line change
Expand Up @@ -729,13 +729,12 @@ PHP_FUNCTION(hash_pbkdf2)
/* }}} */

/* {{{ proto bool hash_equals(string known_string, string user_string)
Compares two strings using the same time whether they're equal or not.
A difference in length will leak */
Compares two strings using the same time whether they're equal or not. */
PHP_FUNCTION(hash_equals)
{
zval *known_zval, *user_zval;
char *known_str, *user_str;
int result = 0, j;
int known_len, user_len, result, j;

if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "zz", &known_zval, &user_zval) == FAILURE) {
return;
Expand All @@ -752,16 +751,19 @@ PHP_FUNCTION(hash_equals)
RETURN_FALSE;
}

if (Z_STRLEN_P(known_zval) != Z_STRLEN_P(user_zval)) {
RETURN_FALSE;
}
known_len = Z_STRLEN_P(known_zval);
user_len = Z_STRLEN_P(user_zval);

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];
/* Set result as different of 0 if strings have a different length. */
result = known_len - user_len;

/* This is security sensitive code. Do not optimize this for speed.
Always iterate on \0 to avoid issues with empty strings. */
for (j = 0; j < user_len + 1; j++) {
result |= known_str[j % (known_len + 1)] ^ user_str[j];
}

RETURN_BOOL(0 == result);
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