From: Eli Zaretskii <eliz@gnu.org>
To: npostavs@users.sourceforge.net
Cc: 24751@debbugs.gnu.org
Subject: bug#24751: 26.0.50; Regex stack overflow not detected properly (gets "Variable binding depth exceeds max-specpdl-size")
Date: Sun, 13 Nov 2016 18:12:47 +0200 [thread overview]
Message-ID: <83a8d3cq9s.fsf@gnu.org> (raw)
In-Reply-To: <87a8d4lyzo.fsf@users.sourceforge.net> (npostavs@users.sourceforge.net)
> From: npostavs@users.sourceforge.net
> Cc: 24751@debbugs.gnu.org
> Date: Sun, 13 Nov 2016 00:39:39 -0500
>
> > I think the patch can be simplified, where we now multiply by the size
> > of fail_stack_elt_t and then divide by it: simply remove both the
> > multiplication and the division. That will make the code easier to
> > read, and will make the units of each variable clear, something that I
> > think is at the heart of this issue.
>
> Ah, right.
Thanks, LGTM.
> >> but effectively increases the size of the failure stack (so the
> >> sample file size has to be increased 8-fold to get a regex stack
> >> overflow).
> >
> > Which IMO is exactly TRT, since re_max_failures was computed given the
> > runtime stack size of 8MB, so having it bail out after merely 800KB
> > doesn't sound right to me, don't you agree?
>
> Yes, I suppose we should also try to make use of the stack, rather than
> calling malloc, right? Something like this:
>
> diff --git i/src/regex.c w/src/regex.c
> index d23ba01..dcabde5 100644
> --- i/src/regex.c
> +++ w/src/regex.c
> @@ -447,7 +447,11 @@ init_syntax_once (void)
> #else /* not REGEX_MALLOC */
>
> # ifdef emacs
> -# define REGEX_USE_SAFE_ALLOCA USE_SAFE_ALLOCA
> +# define REGEX_USE_SAFE_ALLOCA \
> + ptrdiff_t sa_avail = re_max_failures \
> + * TYPICAL_FAILURE_SIZE * sizeof (fail_stack_elt_t); \
> + ptrdiff_t sa_count = SPECPDL_INDEX (); bool sa_must_free = false
> +
Yes. And please also add a comment there saying that this replaces
USE_SAFE_ALLOCA.
> -size_t re_max_failures = 40000;
> +size_t re_max_failures = 20;
> # else
> size_t re_max_failures = 4000;
> # endif
>
>
> Actually I find Emacs still compiles if I removed that line completely,
> there's just a compile warning saying
>
> regex.o: In function `re_match_2_internal':
> /home/npostavs/src/emacs/emacs-master/lib-src/../src/regex.c:5529: warning: the 're_max_failures' variable is obsolete and will go away.
>
> I guess there's some kind of definition of it in libc?
Most probably. You should be able to see that using "nm -A". If
that's indeed so, I think we should rename that variable to something
like emacs_re_max_failures, to avoid stomping on the libc variable..
next prev parent reply other threads:[~2016-11-13 16:12 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-21 3:54 bug#24751: 26.0.50; Regex stack overflow not detected properly (gets "Variable binding depth exceeds max-specpdl-size") npostavs
2016-11-04 8:22 ` Eli Zaretskii
2016-11-05 19:34 ` npostavs
2016-11-06 15:45 ` Eli Zaretskii
2016-11-13 5:39 ` npostavs
2016-11-13 16:12 ` Eli Zaretskii [this message]
2016-11-15 3:08 ` npostavs
2016-11-15 16:12 ` Eli Zaretskii
2016-11-16 1:06 ` npostavs
2016-11-16 16:25 ` Eli Zaretskii
2016-11-16 23:25 ` npostavs
2016-11-17 16:21 ` Eli Zaretskii
2016-11-19 10:02 ` Eli Zaretskii
2017-01-01 18:33 ` npostavs
2017-01-01 18:41 ` Eli Zaretskii
2017-01-01 18:57 ` npostavs
2017-01-01 20:06 ` Eli Zaretskii
2017-01-02 4:49 ` npostavs
2017-01-02 15:24 ` Eli Zaretskii
2017-01-02 18:30 ` npostavs
2017-01-02 19:22 ` Eli Zaretskii
2017-01-08 23:49 ` npostavs
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