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Date: Mon, 8 Feb 2010 15:07:47 +0800
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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>
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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>, linux-fsdevel@vger.kernel.org,
	Serge Hallyn <serue@us.ibm.com>, Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
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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
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 goto out_unlock;
>> =C2=A0 =C2=A0 =C2=A0 }
>>
>> + =C2=A0 =C2=A0 stack_base =3D min(EXTRA_STACK_VM_PAGES * PAGE_SIZE,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0current->signal->rlim[RLIMIT_STACK].rlim_cur -
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0PAGE_SIZE);
>
> This line is a bit unclear why "- PAGE_SIZE" is necessary.
> personally, I like following likes explicit comments.
>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0stack_expand =3D EXTRA_STACK_VM_PAGES * PAGE_S=
IZE;
> =C2=A0 =C2=A0 =C2=A0 =C2=A0stack_lim =3D ACCESS_ONCE(rlim[RLIMIT_STACK].r=
lim_cur);
>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0/* Initial stack must not cause stack overflow=
. */
> =C2=A0 =C2=A0 =C2=A0 =C2=A0if (stack_expand + PAGE_SIZE > stack_lim)
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0stack_expand =3D s=
tack_lim - PAGE_SIZE;
>
> note: accessing rlim_cur require ACCESS_ONCE.
>
>
> Thought?

It's better to use the helper function: rlimit().