From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH v6] Added PR_SET_PROCTITLE_AREA option for prctl()
Cc: kosaki.motohiro@jp.fujitsu.com, Bryan Donlan <bdonlan@gmail.com>,
       Ulrich Drepper <drepper@redhat.com>, Timo Sirainen <tss@iki.fi>,
       WANG Cong <xiyou.wangcong@gmail.com>, Oleg Nesterov <oleg@redhat.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>
In-Reply-To: <20091209091023.GD5129@elte.hu>
References: <20091208161838.B5BD.A69D9226@jp.fujitsu.com> <20091209091023.GD5129@elte.hu>
Message-Id: <20091210091537.F4F7.A69D9226@jp.fujitsu.com>
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Date: Thu, 10 Dec 2009 09:16:09 +0900 (JST)
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> 
> * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> 
> > > 
> > > * Bryan Donlan <bdonlan@gmail.com> wrote:
> > > 
> > > > On Tue, Dec 8, 2009 at 12:38 AM, Ingo Molnar <mingo@elte.hu> wrote:
> > > > >
> > > > > * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> > > > >
> > > > >> > The feature looks useful, but the choice of a prctl as an API is strange
> > > > >> > - it limits us to the current task only - while the ability to set
> > > > >> > arguments for another task looks a more generic (and potentially more
> > > > >> > useful) solution.
> > > > >>
> > > > >> No. It's impossible.
> > > > >> /proc/{pid}/cmdline read user process's memory. iow, this prctl() don't
> > > > >> receive string, it receive virtual address itself. [...]
> > > > >
> > > > > it's not 'impossible' at all, you yourself mention ptrace:
> > > > 
> > > > If another process is going to use ptrace to inject the cmdline string 
> > > > into the victim's address space, it can also temporarily hijack a 
> > > > thread to run prctl() on its behalf...
> > > 
> > > That's exactly the point i made. There's no reason not to offer the API 
> > > i suggested as long as permissions are checked (as usual) - because 
> > > ptrace already allows this (and more).
> > 
> > Confused.
> > 
> > I think ptrace don't solve the issue of explained my patch description.
> 
> it doesnt. By 'this' i meant the security aspect. ptrace can already do 
> almost arbitrary alteration to any task's state.

Ah, I misunderstood. Thanks correct me :)


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