linux-kernel - Re: [rfc 1/4] mm: Introduce may_adjust

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Message-ID: <20140724192152.GC17876@moon>
Date:	Thu, 24 Jul 2014 23:21:52 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	Julien Tinnes <jln@...gle.com>
Subject: Re: [rfc 1/4] mm: Introduce may_adjust_brk helper

On Thu, Jul 24, 2014 at 12:18:56PM -0700, Kees Cook wrote:
> >
> > +static inline int may_adjust_brk(unsigned long rlim,
> > +                                unsigned long new_brk,
> > +                                unsigned long start_brk,
> > +                                unsigned long end_data,
> > +                                unsigned long start_data)
> > +{
> > +       if (rlim < RLIMIT_DATA) {
> 
> Won't rlim always be the value from a call to rlimit(RLIMIT_DATA)? Is
> there a good reason to not just put the rlimit() call in
> may_adjust_brk()? This would actually be an optimization in the
> prctl_set_mm case, since now it calls rlimit() unconditionally, but
> doesn't need to.

Nope, we use it for rlimit(RLIMIT_STACK) when checking for
@start_stack member.
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