Re: [PATCH] Restrict stack space reservation to rlimit

["Américo Wang" <xiyou.wangcong@gmail.com>]

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().