From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?UTF-8?Q?Am=C3=A9rico_Wang?= <xiyou.wangcong@gmail.com>
Subject: Re: [PATCH] Restrict stack space reservation to rlimit
Date: Mon, 8 Feb 2010 15:07:47 +0800
Message-ID: <2375c9f91002072307h4af1ba6dw1b7a598582991dc4@mail.gmail.com>
References: <20100208141716.FB55.A69D9226@jp.fujitsu.com>
	 <9729.1265607469@neuling.org>
	 <20100208145240.FB58.A69D9226@jp.fujitsu.com>
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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
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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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 * PA=
GE_SIZE;
> =C2=A0 =C2=A0 =C2=A0 =C2=A0stack_lim =3D ACCESS_ONCE(rlim[RLIMIT_STAC=
K].rlim_cur);
>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0/* Initial stack must not cause stack over=
flow. */
> =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=
 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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