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Handle zero seed in Xoshiro256** #9250

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Merged
merged 1 commit into from
Aug 5, 2022
Merged

Handle zero seed in Xoshiro256** #9250

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2 changes: 2 additions & 0 deletions NEWS
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@ 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,
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16 changes: 12 additions & 4 deletions ext/random/engine_xoshiro256starstar.c
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Expand Up @@ -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));
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I'm not too happy about hard-coding the number of elements here, but can't come up with a more elegant solution, so I guess it's okay.

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Yeah, it also looked pretty verbose to me. But on the other hand it's not like the number of elements is ever going to change. Any kind of loop would make the code more complex for an extraordinarily uncommon case.

I thought about ORing all the elements together, but that would be less clear (interestingly gcc already optimizes the condition to (state->state[0] | state->state[1] | state->state[2] | state->state[3]) == 0).

} else {
if (str_seed) {
/* char (byte: 8 bit) * 32 = 256 bits */
Expand All @@ -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");
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7 changes: 7 additions & 0 deletions ext/random/tests/02_engine/xoshiro256starstar_seed.phpt
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Expand Up @@ -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($engine);
Expand All @@ -31,6 +37,7 @@ for ($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) {
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