linux-kernel - Re: [tip:x86/mm] x86/mmap, ASLR: Do not treat unlimited-stack tasks as legacy mmap

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Date:   Tue, 27 Jun 2017 10:00:23 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
cc:     tip-bot for Michal Hocko <tipbot@...or.com>,
        linux-tip-commits@...r.kernel.org, torvalds@...ux-foundation.org,
        mingo@...nel.org, hpa@...or.com, mhocko@...e.com,
        tglx@...utronix.de, davej@...emonkey.org.uk, peterz@...radead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [tip:x86/mm] x86/mmap, ASLR: Do not treat unlimited-stack tasks
 as legacy mmap

On Fri, 23 Jun 2017, Oleg Nesterov wrote:

> > We added a heuristics to treat applications with RLIMIT_STACK configured
> > to unlimited as legacy. This means:
> 
> To me this also means a minor security problem. The comment above
> PER_CLEAR_ON_SETID says "must be cleared upon setuid or setgid exec",
> but if you do "ulimit -s unlimited" before suid exec then
> ADDR_COMPAT_LAYOUT set by security checks will be ignored.

Could you please be a bit more specific here?

mmap_is_legacy() *first* checks for the ADDR_COMPAT_LAYOUT in the 
personality flags, and only then, if it's unset, RLIMIT_STACK comes to 
play.

Thanks,

-- 
Jiri Kosina
SUSE Labs