Handle all-zero state in Xoshiro256** (#9250)

- Retry if the CSPRNG generates a zero state.
- Throw ValueError if the user passes a zero state.

Fixes GH-9249

Author: TimWolla

NEWS

@@ -12,6 +12,8 @@ PHP                                                                        NEWS
     PcgOneseq128XslRr64::__construct()). (timwolla)
   . Fixed bug GH-9190, GH-9191 (undefined behavior for MT_RAND_PHP when
     handling large ranges). (timwolla)
+  . Fixed bug GH-9249 (Xoshiro256StarStar does not reject the invalid
+    all-zero state). (timwolla)
   . Removed redundant RuntimeExceptions from Randomizer methods. The
     exceptions thrown by the engines will be exposed directly. (timwolla)
   . Added extension specific Exceptions/Errors (RandomException, RandomError,

ext/random/engine_xoshiro256starstar.c

@@ -205,10 +205,12 @@ PHP_METHOD(Random_Engine_Xoshiro256StarStar, __construct)
 	ZEND_PARSE_PARAMETERS_END();
 
 	if (seed_is_null) {
-		if (php_random_bytes_throw(&state->state, 32) == FAILURE) {
-			zend_throw_exception(random_ce_Random_RandomException, "Failed to generate a random seed", 0);
-			RETURN_THROWS();
-		}
+		do {
+			if (php_random_bytes_throw(&state->state, 32) == FAILURE) {
+				zend_throw_exception(random_ce_Random_RandomException, "Failed to generate a random seed", 0);
+				RETURN_THROWS();
+			}
+		} while (UNEXPECTED(state->state[0] == 0 && state->state[1] == 0 && state->state[2] == 0 && state->state[3] == 0));
 	} else {
 		if (str_seed) {
 			/* char (byte: 8 bit) * 32 = 256 bits */
@@ -222,6 +224,12 @@ PHP_METHOD(Random_Engine_Xoshiro256StarStar, __construct)
 						t[i] += ((uint64_t) (unsigned char) ZSTR_VAL(str_seed)[(i * 8) + j]) << (j * 8);
 					}
 				}
+
+				if (UNEXPECTED(t[0] == 0 && t[1] == 0 && t[2] == 0 && t[3] == 0)) {
+					zend_argument_value_error(1, "must not consist entirely of NUL bytes");
+					RETURN_THROWS();
+				}
+
 				seed256(engine->status, t[0], t[1], t[2], t[3]);
 			} else {
 				zend_argument_value_error(1, "must be a 32 byte (256 bit) string");

ext/random/tests/02_engine/xoshiro256starstar_seed.phpt

@@ -18,6 +18,12 @@ try {
     echo $e->getMessage() . PHP_EOL;
 }
 
+try {
+    $engine = new Random\Engine\Xoshiro256StarStar(\str_repeat("\x00", 32));
+} catch (\Throwable $e) {
+    echo $e->getMessage() . PHP_EOL;
+}
+
 $engine = new \Random\Engine\Xoshiro256StarStar("\x01\x02\x03\x04\x05\x06\x07\x08\x01\x02\x03\x04\x05\x06\x07\x08\x01\x02\x03\x04\x05\x06\x07\x08\x01\x02\x03\x04\x05\x06\x07\x08");
 
 \var_dump($engine);
@@ -31,6 +37,7 @@ for ($i = 0; $i < 1000; $i++) {
 --EXPECTF--
 Random\Engine\Xoshiro256StarStar::__construct(): Argument #1 ($seed) must be of type string|int|null, float given
 Random\Engine\Xoshiro256StarStar::__construct(): Argument #1 ($seed) must be a 32 byte (256 bit) string
+Random\Engine\Xoshiro256StarStar::__construct(): Argument #1 ($seed) must not consist entirely of NUL bytes
 object(Random\Engine\Xoshiro256StarStar)#%d (%d) {
   ["__states"]=>
   array(4) {