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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Americo Wang <xiyou.wangcong@gmail.com>
Subject: Re: [PATCH] Restrict stack space reservation to rlimit
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Date: Mon,  8 Feb 2010 16:11:47 +0900 (JST)
Cc: Michael Neuling <mikey@neuling.org>, stable@kernel.org, aeb@cwi.nl,
	Oleg Nesterov <oleg@redhat.com>, miltonm@bga.com,
	James Morris <jmorris@namei.org>, linuxppc-dev@ozlabs.org,
	Paul Mackerras <paulus@samba.org>, Anton Blanchard <anton@samba.org>,
	kosaki.motohiro@jp.fujitsu.com, linux-fsdevel@vger.kernel.org,
	Serge Hallyn <serue@us.ibm.com>, Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>
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> On Mon, Feb 8, 2010 at 2:05 PM, KOSAKI Motohiro
> <kosaki.motohiro@jp.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.