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Detect immediate double-frees of zend_mm small slots #23360

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Detect immediate double-frees of zend_mm small slots #23360

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6 changes: 6 additions & 0 deletions Zend/zend_alloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1430,6 +1430,12 @@ static zend_always_inline void zend_mm_free_small(zend_mm_heap *heap, void *ptr,
#endif

p = (zend_mm_free_slot*)ptr;
#if ZEND_MM_HEAP_PROTECTION
/* Catch the most common double-free pattern for free. */
if (UNEXPECTED(p == heap->free_slot[bin_num])) {
zend_mm_panic("zend_mm_heap corrupted (double free)");
}
#endif
zend_mm_set_next_free_slot(heap, bin_num, p, heap->free_slot[bin_num]);
heap->free_slot[bin_num] = p;
}
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