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Fix use after free during shutdown destruction #18834

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Fix use after free during shutdown destruction #18834

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ea2d621
Fix use after free during shutdown destruction
danog Jun 11, 2025
81f808e
Bump news
danog Jun 11, 2025
5135728
Add test
danog Jun 11, 2025
7dc3b03
Improve fix
danog Jun 16, 2025
487f644
Add parentheses
danog Jun 16, 2025
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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 @@ -3,6 +3,8 @@ PHP NEWS
?? ??? ????, PHP 8.3.23

- Core:
. Fixed GH-18833 (use after free during destruction).
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Note for self: move this entry

(Daniil Gentili)
. Fixed GH-18695 (zend_ast_export() - float number is not preserved).
(Oleg Efimov)

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24 changes: 24 additions & 0 deletions Zend/tests/gh18833.phpt
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@@ -0,0 +1,24 @@
--TEST--
Bug #18833 (Use after free with weakmaps dependent on destruction order)
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Nit: For bugs on github, it's supposed to be GH-18833 instead of a pound sign. I'll fix this in the merge

--FILE--
<?php

class a {
public static WeakMap $map;
public static Generator $storage;
}

a::$map = new WeakMap;

$closure = function () {
$obj = new a;
a::$map[$obj] = true;
yield $obj;
};
a::$storage = $closure();
a::$storage->current();

echo "ok\n";
?>
--EXPECT--
ok
36 changes: 10 additions & 26 deletions Zend/zend_objects_API.c
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Expand Up @@ -97,33 +97,17 @@ ZEND_API void ZEND_FASTCALL zend_objects_store_free_object_storage(zend_objects_
end = objects->object_buckets + 1;
obj_ptr = objects->object_buckets + objects->top;

if (fast_shutdown) {
do {
obj_ptr--;
obj = *obj_ptr;
if (IS_OBJ_VALID(obj)) {
if (!(OBJ_FLAGS(obj) & IS_OBJ_FREE_CALLED)) {
GC_ADD_FLAGS(obj, IS_OBJ_FREE_CALLED);
if (obj->handlers->free_obj != zend_object_std_dtor) {
GC_ADDREF(obj);
obj->handlers->free_obj(obj);
}
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We skipped zend_object_std_dtor() calls because we didn't need to deallocate the memory for each property separately. We relayed on Zend MM to deallocate all the request memory at once.

The problem was introduced by weak references that added notification in free_obj calback.
I'm not sure if this was a right/best place.
I think, a better quick fix would be checking IS_OBJ_WEAKLY_REFERENCED flag.

}
}
} while (obj_ptr != end);
} else {
do {
obj_ptr--;
obj = *obj_ptr;
if (IS_OBJ_VALID(obj)) {
if (!(OBJ_FLAGS(obj) & IS_OBJ_FREE_CALLED)) {
GC_ADD_FLAGS(obj, IS_OBJ_FREE_CALLED);
GC_ADDREF(obj);
obj->handlers->free_obj(obj);
}
do {
obj_ptr--;
obj = *obj_ptr;
if (IS_OBJ_VALID(obj)) {
if (!(OBJ_FLAGS(obj) & IS_OBJ_FREE_CALLED)) {
GC_ADD_FLAGS(obj, IS_OBJ_FREE_CALLED);
GC_ADDREF(obj);
obj->handlers->free_obj(obj);
}
} while (obj_ptr != end);
}
}
} while (obj_ptr != end);
}


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