Date: Tue, 8 Dec 2009 07:57:25 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Bryan Donlan <bdonlan@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.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>
Subject: Re: [PATCH v6] Added PR_SET_PROCTITLE_AREA option for prctl()
Message-ID: <20091208065725.GA21340@elte.hu>
References: <20091208121145.B58D.A69D9226@jp.fujitsu.com>
 <20091208044605.GA32669@elte.hu>
 <20091208135010.B5A8.A69D9226@jp.fujitsu.com>
 <20091208053851.GA12383@elte.hu>
 <3e8340490912072228m70368001v2487bd745ff208b3@mail.gmail.com>
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* 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).

Thanks,

	Ingo
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