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Date: Mon, 8 Feb 2010 15:07:47 +0800
Message-ID: <2375c9f91002072307h4af1ba6dw1b7a598582991dc4@mail.gmail.com>
Subject: Re: [PATCH] Restrict stack space reservation to rlimit
From: =?UTF-8?Q?Am=C3=A9rico_Wang?= <xiyou.wangcong@gmail.com>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michael Neuling <mikey@neuling.org>, Anton Blanchard <anton@samba.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Alexander Viro <viro@zeniv.linux.org.uk>,
       Oleg Nesterov <oleg@redhat.com>, James Morris <jmorris@namei.org>,
       Ingo Molnar <mingo@elte.hu>, linux-fsdevel@vger.kernel.org,
       stable@kernel.org, linux-kernel@vger.kernel.org,
       linuxppc-dev@ozlabs.org, Serge Hallyn <serue@us.ibm.com>,
       Paul Mackerras <paulus@samba.org>, benh@kernel.crashing.org,
       miltonm@bga.com, aeb@cwi.nl
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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().
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