Fix use-after-free in extract() EXTR_REFS collision modes#155
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The phpGH-18209 fix guarded only php_extract_ref_overwrite. The other five per-collision-mode helpers (if_exists, prefix_if_exists, prefix_same, prefix_all, prefix_invalid), split out when extract() was refactored, kept the pre-fix order: they dropped the old value of orig_var before writing the new reference. A destructor run by that drop can unset the symbol being written, so the following ZVAL_REF wrote into freed memory. Apply the same swap-then-dtor already used by php_extract_ref_overwrite: copy the old value aside, write the reference, then drop the copy. Fixes phpGH-18209
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Submitted upstream as php#22696. |
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The phpGH-18209 fix guarded only php_extract_ref_overwrite. The other five per-collision-mode helpers (if_exists, prefix_if_exists, prefix_same, prefix_all, prefix_invalid), split out when extract() was refactored, kept the pre-fix order: they dropped the old value of orig_var before writing the new reference, so a destructor run by that drop that frees the target symbol makes the following ZVAL_REF a use-after-free. This applies the same swap-then-dtor already used by php_extract_ref_overwrite (copy the old value aside, write the reference, then drop the copy). Reproduces with extract($a, EXTR_REFS | EXTR_IF_EXISTS) when the target variable holds an object whose destructor unsets it.