linux-kernel - Re: [PATCH] Restrict stack space reservation to rlimit

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Message-Id: <20100208161014.7C6D.A69D9226@jp.fujitsu.com>
Date:	Mon,  8 Feb 2010 16:11:47 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Americo Wang <xiyou.wangcong@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Michael Neuling <mikey@...ling.org>,
	Anton Blanchard <anton@...ba.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	James Morris <jmorris@...ei.org>, Ingo Molnar <mingo@...e.hu>,
	linux-fsdevel@...r.kernel.org, stable@...nel.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Serge Hallyn <serue@...ibm.com>,
	Paul Mackerras <paulus@...ba.org>, benh@...nel.crashing.org,
	miltonm@....com, aeb@....nl
Subject: Re: [PATCH] Restrict stack space reservation to rlimit

> On Mon, Feb 8, 2010 at 2:05 PM, KOSAKI Motohiro
> <kosaki.motohiro@...fujitsu.com> wrote:
> >> --- linux-2.6-ozlabs.orig/fs/exec.c
> >> +++ linux-2.6-ozlabs/fs/exec.c
> >> @@ -627,10 +627,13 @@ int setup_arg_pages(struct linux_binprm
> >>                       goto out_unlock;
> >>       }
> >>
> >> +     stack_base = min(EXTRA_STACK_VM_PAGES * PAGE_SIZE,
> >> +                      current->signal->rlim[RLIMIT_STACK].rlim_cur -
> >> +                        PAGE_SIZE);
> >
> > This line is a bit unclear why "- PAGE_SIZE" is necessary.
> > personally, I like following likes explicit comments.
> >
> >        stack_expand = EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> >        stack_lim = ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur);
> >
> >        /* Initial stack must not cause stack overflow. */
> >        if (stack_expand + PAGE_SIZE > stack_lim)
> >                stack_expand = stack_lim - PAGE_SIZE;
> >
> > note: accessing rlim_cur require ACCESS_ONCE.
> >
> >
> > Thought?
> 
> It's better to use the helper function: rlimit().

AFAIK, stable tree doesn't have rlimit(). but yes, making two patch
(for mainline and for stable) is good opinion.



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