crypt: Fix validation of malformed BCrypt hashes

PHP’s implementation of crypt_blowfish differs from the upstream Openwall
version by adding a “PHP Hack”, which allows one to cut short the BCrypt salt
by including a `$` character within the characters that represent the salt.

Hashes that are affected by the “PHP Hack” may erroneously validate any
password as valid when used with `password_verify` and when comparing the
return value of `crypt()` against the input.

The PHP Hack exists since the first version of PHP’s own crypt_blowfish
implementation that was added in 1e820ec.

No clear reason is given for the PHP Hack’s existence. This commit removes it,
because BCrypt hashes containing a `$` character in their salt are not valid
BCrypt hashes.

Author: TimWolla

ext/standard/crypt_blowfish.c

@@ -371,7 +371,6 @@ static const unsigned char BF_atoi64[0x60] = {
 #define BF_safe_atoi64(dst, src) \
 { \
 	tmp = (unsigned char)(src); \
-	if (tmp == '$') break; /* PHP hack */ \
 	if ((unsigned int)(tmp -= 0x20) >= 0x60) return -1; \
 	tmp = BF_atoi64[tmp]; \
 	if (tmp > 63) return -1; \
@@ -399,13 +398,6 @@ static int BF_decode(BF_word *dst, const char *src, int size)
 		*dptr++ = ((c3 & 0x03) << 6) | c4;
 	} while (dptr < end);
 
-	if (end - dptr == size) {
-		return -1;
-	}
-
-	while (dptr < end) /* PHP hack */
-		*dptr++ = 0;
-
 	return 0;
 }
 

ext/standard/tests/crypt/bcrypt_salt_dollar.phpt

@@ -0,0 +1,82 @@
+--TEST--
+bcrypt correctly rejects salts containing $
+--FILE--
+<?php
+for ($i = 0; $i < 23; $i++) {
+	$salt = '$2y$04$' . str_repeat('0', $i) . '$';
+	$result = crypt("foo", $salt);
+	var_dump($salt);
+	var_dump($result);
+	var_dump($result === $salt);
+}
+?>
+--EXPECT--
+string(8) "$2y$04$$"
+string(2) "*0"
+bool(false)
+string(9) "$2y$04$0$"
+string(2) "*0"
+bool(false)
+string(10) "$2y$04$00$"
+string(2) "*0"
+bool(false)
+string(11) "$2y$04$000$"
+string(2) "*0"
+bool(false)
+string(12) "$2y$04$0000$"
+string(2) "*0"
+bool(false)
+string(13) "$2y$04$00000$"
+string(2) "*0"
+bool(false)
+string(14) "$2y$04$000000$"
+string(2) "*0"
+bool(false)
+string(15) "$2y$04$0000000$"
+string(2) "*0"
+bool(false)
+string(16) "$2y$04$00000000$"
+string(2) "*0"
+bool(false)
+string(17) "$2y$04$000000000$"
+string(2) "*0"
+bool(false)
+string(18) "$2y$04$0000000000$"
+string(2) "*0"
+bool(false)
+string(19) "$2y$04$00000000000$"
+string(2) "*0"
+bool(false)
+string(20) "$2y$04$000000000000$"
+string(2) "*0"
+bool(false)
+string(21) "$2y$04$0000000000000$"
+string(2) "*0"
+bool(false)
+string(22) "$2y$04$00000000000000$"
+string(2) "*0"
+bool(false)
+string(23) "$2y$04$000000000000000$"
+string(2) "*0"
+bool(false)
+string(24) "$2y$04$0000000000000000$"
+string(2) "*0"
+bool(false)
+string(25) "$2y$04$00000000000000000$"
+string(2) "*0"
+bool(false)
+string(26) "$2y$04$000000000000000000$"
+string(2) "*0"
+bool(false)
+string(27) "$2y$04$0000000000000000000$"
+string(2) "*0"
+bool(false)
+string(28) "$2y$04$00000000000000000000$"
+string(2) "*0"
+bool(false)
+string(29) "$2y$04$000000000000000000000$"
+string(2) "*0"
+bool(false)
+string(30) "$2y$04$0000000000000000000000$"
+string(60) "$2y$04$000000000000000000000u2a2UpVexIt9k3FMJeAVr3c04F5tcI8K"
+bool(false)