Re: [PATCH] mm: larger stack guard gap, between vmas

From: Willy Tarreau
Date: Wed Jul 05 2017 - 15:00:25 EST

On Wed, Jul 05, 2017 at 09:17:59AM -0700, Linus Torvalds wrote:
> The good news is that this is probably specialized enough that we can
> just keep the defaults as "will break this one case, but we give
> people the tools to work around it".
> I hate doing that, but distros that still support 32-bit (which is
> apparently a shrinking number) can maybe hack the libreoffice launch
> scripts up?

Don't you think that the option of having a sysctl to relax the check
per task wouldn't be easier for distros and safer overall ? Ie, emit
a warning the first time the gap is hit instead of segfaulting, then
reduce it to something that used to work (4k or 64k, I don't remember)
and try again ? It would quickly report all these "special" programs
for end-user distros, without leaving too much room for attacks due
to the warning making it pretty obvious what's going on. I just don't
know how to place this stack gap per process but since this was already
discussed for prctl I think it's doable.