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

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Message-ID: <20170704155140.GC22013@1wt.eu>
Date:   Tue, 4 Jul 2017 17:51:40 +0200
From:   Willy Tarreau <w@....eu>
To:     Ben Hutchings <ben@...adent.org.uk>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Tony Luck <tony.luck@...el.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Diller <deller@....de>,
        James Hogan <james.hogan@...tec.com>,
        Laura Abbott <labbott@...hat.com>, Greg KH <greg@...ah.com>,
        "security@...nel.org" <security@...nel.org>,
        linux-distros@...openwall.org,
        Qualys Security Advisory <qsa@...lys.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ximin Luo <infinity0@...ian.org>
Subject: Re: [PATCH] mm: larger stack guard gap, between vmas

On Tue, Jul 04, 2017 at 12:36:11PM +0100, Ben Hutchings wrote:
> > If anywhing this would require to have a loop over all PROT_NONE
> > mappings to not hit into other weird usecases.
> 
> That's what I was thinking of.  Tried the following patch:
(...)
> -	next = vma->vm_next;
> +	/*
> +	 * Allow VM_NONE mappings in the gap as some applications try
> +	 * to make their own stack guards
> +	 */
> +	for (next = vma->vm_next;
> +	     next && !(next->vm_flags & (VM_READ | VM_WRITE | VM_EXEC));
> +	     next = next->vm_next)
> +		;

That's what I wanted to propose but I feared someone would scream at me
for this loop :-)

+1 for me!

Willy