[pull] master from ruby:master#1164
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pm_setup_args mallocs one kw_arg buffer with references = 0. The inline_new branch then feeds that same pointer to three callinfo constructions: - 3789 — new_callinfo(... method_id="new" ..., kw_arg, 0) -> the opt_new ci - 3795 — PUSH_SEND_R(... "initialize", ..., flags | VM_CALL_FCALL, kw_arg) - 3800 — PUSH_SEND_R(... method_id="new", ..., flags, kw_arg) (fallback) Tracing the refcount through rb_vm_ci_lookup() 1. It increments kwarg->references and allocates a fresh new_ci before the dedup st_update 2. The dedup (vm_ci_hash_cmp) compares kwarg contents, not the pointer. So if an earlier line already interned a new ci with the identical keyword set, st_update returns that pre-existing ci (which holds a different buffer) and discards our new_ci. 3. Our kw_arg is now orphaned: references == 1, but the only holder is the discarded new_ci, which is a normal collectable imemo 4. An allocation like PUSH_INSN2 opt_new at or new_callinfo() can trigger a GC. References back to 0, kw_arg buffer freed. 5. new_callinfo() using the freed buffer, does argc += kw_arg->keyword_len (use-after-free) The fix: Keep the buffer alive across the allocations in inline_new. Fixes [Bug #22104]
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