Subject: Re: bug#58334: 29.0.50; ASAN heap use after free in gui_produce_glyphs

From: Po Lu <[email-masked]>
Date: Fri, 07 Oct 2022 20:12:58 +0800

Gerd Möllmann <[email-masked]> writes:

> int count = inhibit_garbahe_collection ();
> redisplay ();
> unbind_to...

Why would you only inhibit garbage collection there?  What if some
finalizer function calls preedit text inside process_pending_signals?

Also, what about where we decode X preconversion text?

In the recent past, Emacs also used to run Lisp as part of the character
conversion of keyboard input, straight from handle_one_xevent:

	    if (nchars < nbytes)
	      {
		/* Decode the input data.  */

		/* The input should be decoded with `coding_system'
		   which depends on which X*LookupString function
		   we used just above and the locale.  */
		setup_coding_system (coding_system, &coding);
		coding.src_multibyte = false;
		coding.dst_multibyte = true;
		/* The input is converted to events, thus we can't
		   handle composition.  Anyway, there's no XIM that
		   gives us composition information.  */
		coding.common_flags &= ~CODING_ANNOTATION_MASK;

		SAFE_NALLOCA (coding.destination, MAX_MULTIBYTE_LENGTH,
			      nbytes);
		coding.dst_bytes = MAX_MULTIBYTE_LENGTH * nbytes;
		coding.mode |= CODING_MODE_LAST_BLOCK;
		decode_coding_c_string (&coding, copy_bufptr, nbytes, Qnil);
		nbytes = coding.produced;
		nchars = coding.produced_char;
		copy_bufptr = coding.destination;
	      }

How come that never caused problems?

Thanks.