linux-kernel - Re: [PATCH 2/2] execve: check the VM has enough memory at first

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Message-Id: <20100916111714.CA03.A69D9226@jp.fujitsu.com>
Date:	Thu, 16 Sep 2010 14:51:55 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, oss-security@...ts.openwall.com,
	Solar Designer <solar@...nwall.com>,
	Kees Cook <kees.cook@...onical.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	linux-fsdevel@...r.kernel.org, pageexec@...email.hu,
	"Brad Spengler <spender@...ecurity.net>, Eugene Teo" 
	<eugene@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/2] execve: check the VM has enough memory at first

> > On Wed, Sep 8, 2010 at 10:04 PM, KOSAKI Motohiro
> > <kosaki.motohiro@...fujitsu.com> wrote:
> > >
> > > After this patch, execve() expand stack at first and receive to
> > > check vm_enough_memory() properly. then, too long argument of
> > > execve() than the machine memory return EFAULT properly.
> > 
> > This is horrible. We don't want to walk the arguments one more time
> > just for this. Let's just improve the checks that we do as we go
> > along.
> > 
> >                             Linus
> 
> Okey. I'll consider new way in this night.

After while thinking, I decided to just drop this idea. because
 1) If one pass check is must, we can't reuse vm-overcommit check.
 2) Glibc has the duplicated hueristic, then we can't change it nor
    introduce new hard limit. (Sh*t)
 3) This is not must fix, it only mitigate a pain when accidental large
    argv case. Only OOM fixes enough care intended attack case.
 4) distro can change default of rlim_max of RLIMIT_STACK. It protect
    from RLIM_INFINITY smash.

Briefly says, to introduce new limit has bad benefit/risk balance. Sadly.



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