Re: [PATCH] Add nil check for decoding buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Lukas Fürmetz <fuermetz@mailbox.org>
> Date: Tue, 10 Apr 2018 23:44:22 +0200
> 
> This patch prevents a emacs crash under Windows for me. Sometimes the
> buffer is split between \r\n and the \n is carried over, but the
> decoding_buf is NIL, so "SCHARS (p->decoding_buf)" leads to a SEGFAULT.
> 
> Would be nice, if this is backported to emacs-26..
> 
> Best regards,
> Lukas
> 
> ---
>  src/process.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/process.c b/src/process.c
> index c357a8bdc3..ab2e6ce4da 100644
> --- a/src/process.c
> +++ b/src/process.c
> @@ -5996,7 +5996,7 @@ read_and_dispose_of_process_output (struct Lisp_Process *p, char *chars,
> 
>    if (coding->carryover_bytes > 0)
>      {
> -      if (SCHARS (p->decoding_buf) < coding->carryover_bytes)
> +      if (NILP (p->decoding_buf) || (SCHARS (p->decoding_buf) < coding->carryover_bytes))
>  	pset_decoding_buf (p, make_uninit_string (coding->carryover_bytes));
>        memcpy (SDATA (p->decoding_buf), coding->carryover,
>  	      coding->carryover_bytes);

Thanks, but I don't think this is the right fix for the problem.
Every process object must have an associated decoding_buf, so if some
process doesn't, it's a bug in that process's creation code.  My
reading of the code is that all the process types we support have
decoding_buf defined during creation -- except one: make-pipe-process
fails to do that.  So the fix should be in make-pipe-process.

Is the problem reproducible, or do you remember what you did when it
happened?  I'd like to make sure that indeed some pipe process was
involved in the crash, because otherwise I don't see how it could
happen.