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

From: Willy Tarreau
Date: Wed Jul 05 2017 - 15:19:34 EST

On Wed, Jul 05, 2017 at 12:17:20PM -0700, Linus Torvalds wrote:
> On Wed, Jul 5, 2017 at 11:59 AM, Willy Tarreau <w@xxxxxx> wrote:
> >
> > 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 used to be just 4k.
> .. and I think that might be a valid way to find these things, but
> would it be safer? It basically disables the new stack gap entirely
> apart from the warning.

But only if the sysctl is set. It can simply be recommended to set it
if any program fails. We've done this for many years with other ones
like min_mmap_addr or tcp_ecn.