Keep dumped objects alive across __debugInfo() and property hooks - #125
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Keep dumped objects alive across __debugInfo() and property hooks#125iliaal wants to merge 1 commit into
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php_var_dump(), php_debug_zval_dump() and php_var_export() capture the object, invoke a userland callback while holding a raw pointer to it, then read its class, handle, properties or refcount. var_dump() and debug_zval_dump() call __debugInfo() through zend_get_properties_for(ZEND_PROP_PURPOSE_DEBUG); var_export() reads property values, which may run a get hook. A user error handler triggered from any of these can drop the last reference to the object, for example by nulling a reference that aliases the dumped array slot, freeing it before those reads and causing a use-after-free. Hold a reference on the object across the callback and read its identity through the captured zend_object pointer instead of re-dereferencing the zval, whose contents the handler may also have replaced. The debug_zval_dump() output reports the refcount without this temporary reference. Fixes phpGH-21024
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Submitted upstream as php#22471. |
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var_dump() and debug_zval_dump() can use-after-free an object when its __debugInfo() triggers a user error handler that frees the object, for example by nulling a reference that aliases the dumped array slot. Both functions hold a raw pointer to the object across the __debugInfo() call and read its class name, handle and properties afterwards.
Fix: hold a reference on the object across zend_get_properties_for() and read its identity through the captured zend_object pointer rather than the zval, releasing the reference after the dump. debug_zval_dump() reports the refcount without the temporary reference.
This crashes on master with a plain synchronous handler, independent of error-handler timing. One of the reports aggregated under phpGH-20018. Verified red-before/green-after.