GNU bug report logs - #18410
Use SAFE_ALLOCA etc. to avoid unbounded stack allocation.

Previous Next

Full log

Message #55 received at 18410 <at> debbugs.gnu.org (full text, mbox):

From: "Demetrios Obenour" <demetriobenour <at> gmail.com>
To: "'Paul Eggert'" <eggert <at> cs.ucla.edu>,
 "'Stefan Monnier'" <monnier <at> iro.umontreal.ca>
Cc: 18410 <at> debbugs.gnu.org
Subject: RE: bug#18410: Use SAFE_ALLOCA etc. to avoid unbounded stack
 allocation.
Date: Sun, 7 Sep 2014 23:17:30 -0400

This is crucial. Otherwise, a security vulnerability could result.

MAX_ALLOCA should not be larger than the page size for the target architecture.

Demetrios Obenour

-----Original Message-----
From: bug-gnu-emacs-bounces+demetriobenour=gmail.com <at> gnu.org [mailto:bug-gnu-emacs-bounces+demetriobenour=gmail.com <at> gnu.org] On Behalf Of Paul Eggert
Sent: Sunday, September 7, 2014 10:38 PM
To: Stefan Monnier
Cc: 18410 <at> debbugs.gnu.org
Subject: bug#18410: Use SAFE_ALLOCA etc. to avoid unbounded stack allocation.

Stefan Monnier wrote:
> MAX_ALLOCA is chosen small so that we can allocate several/many 
> objects of size MAX_ALLOCA.

That's one reason, but another is that stack-overflow checking often relies on guard pages.  If we blindly increase MAX_ALLOCA (or some variant of it, just for call-process) Emacs could bypass stack-overflow checking, resulting in behavior that could be worse than simply dumping core.

If I understand things correctly, Dmitry's recent stack-overflow changes don't affect this, as they don't deal with the guard-page region size.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.