bug#58042: 29.0.50; ASAN use-after-free in re_match_2_internal

[Po Lu]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Can somone please help me understand how this works?
>
> Let's say we are in memq called for list L.  Fmemq uses FOR_EACH_TAIL,
> which can call maybe_quit, which executes arbitrary Lisp, which can
> modify L.  And probably similarly in another 100 places.
>
> I don't get it.

AFAIU if it is particularly dangerous to modify L there, then input
should be blocked around Fmemq.