Prevent resumption of generator suspended in yield from #19315
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Our PRs clashed. #19313 But mine fails, so I trust your solution is better. 😄 |
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Oops :) I did assign the bug to myself before starting working on the fix, but I know it's easy to miss as I did a few times in the past. |
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I found a way to make this still crash: class It implements IteratorAggregate {
public function getIterator(): Generator {
yield "";
Fiber::suspend();
}
}
function g() {
yield from new It();
}
$b = g();
$b->rewind();
$fiber = new Fiber(function () use ($b) {
$b->next();
});
$fiber->start();
try {
$b->throw(new Exception('test'));
} catch (Error $e) {
echo $e->getMessage(), "\n";
} |
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This PR seems right to me. @iluuu1994 Your crash is unrelated, e.g. |
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@bwoebi Don't think it's unrelated. It results in the same uaf. It happens for the same reason ( Details
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I'm saying that the problem here is that throw() is being permitted to be called regardless of ZEND_GENERATOR_CURRENTLY_RUNNING (as long as they're not actually resumed), which is a much broader bug, unlike send() and next() which fail early. Specifically: zend_generator_throw_exception needs to check for it. |
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Ah ok. Yes, preventing |
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I will send a separate PR for the throw issue then. |
bwoebi
approved these changes
Jul 30, 2025
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Normally we prevent generators from being resumed while they are already running, but we failed to do so for generators delegating to non-Generators. As a result such generator can be resumed, terminated, which causes unexpected results (crashes) later.
In GH-19306 in particular, the generator delegate
It::getIterator()suspends while being called by generatorg(). We then resumeg(), which throws while trying to resumeIt::getIterator(). This causesg()andIt::getIterator()to be released. We then crash while resuming the Fiber inIt::getIterator().Fix this by ensuring that generators are marked as running while they fetch the next value from the delegate.
Fixes GH-19306