bug#63063: CVE-2021-36699 report

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Po Lu <luangruo@yahoo.com>
>> Cc: fuomag9 <fuo@fuo.fi>,  63063@debbugs.gnu.org
>> Date: Tue, 25 Apr 2023 15:24:31 +0800
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> > Please tell more about the buffer overflow: where does it happen in
>> > the Emacs sources, which buffer overflows, and why.  I cannot find
>> > these details in your report.
>> 
>> It happens because the dump file is deliberately edited to be invalid.
>
> I didn't ask about the root cause, I asked about the details of the
> problem: where it happens in our sources, and what exactly happens.

The protection fault is in `dump_do_emacs_relocation'.  When the dump
file contains a relocation with an offset outside the heap:

        lv = make_lisp_ptr (obj_ptr, reloc.length);
        memcpy (emacs_ptr_at (reloc.emacs_offset), &lv, sizeof (lv));

will end up copying outside the heap.