Fix use-after-free when json_encode() re-enters an ArrayObject - #22921
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Fix use-after-free when json_encode() re-enters an ArrayObject#22921iliaal wants to merge 1 commit into
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spl_array_get_hash_table_ptr() hands out a pointer into the ArrayObject storage without checking whether anything else holds a reference to it. json_encode() takes such a reference for the length of the encode and then runs userland through JsonSerializable::jsonSerialize() and property hooks, so an insert from there grows the table and frees the buckets the encoder is iterating. Separate the array-backed and self-backed cases the way the object-backed case in the same function already does. Closes phpGH-22921
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json_encode() borrows an ArrayObject's storage table for the length of the encode and then runs userland through JsonSerializable::jsonSerialize() and property hooks. spl_array_get_hash_table_ptr() hands that same table back to the write paths, so an insert from the callback grows it and frees the buckets the encoder is iterating; valgrind reports invalid reads in php_json_encode_array() for the array-backed ArrayObject, ArrayIterator and self-backed cases in the test. The object-backed branch of that function already separates when the table is borrowed, so this gives the other two branches the same treatment. Encoding cost is unchanged: the separation only fires while a borrow is outstanding, and the refcount is 1 the rest of the time.
#20725 proposes the same SEPARATE_ARRAY call at the write sites instead. That placement leaves the by-reference auto-vivify path through spl_array_get_dimension_ptr() unprotected, which valgrind still reports as an invalid read, and it does not reach the self-backed case.