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

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Message-ID: <2375c9f91002072307h4af1ba6dw1b7a598582991dc4@mail.gmail.com>
Date:	Mon, 8 Feb 2010 15:07:47 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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().
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