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: <20091208144004.B5AB.A69D9226@jp.fujitsu.com>
References: <20091208053851.GA12383@elte.hu> <20091208144004.B5AB.A69D9226@jp.fujitsu.com>
Message-Id: <20091208155202.B5B7.A69D9226@jp.fujitsu.com>
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Date: Tue,  8 Dec 2009 15:53:21 +0900 (JST)
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> > 
> > * 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:
> 
> Ah yes, 'impossible' was wrong word. but it doesn't works intentionally.
> 
> 1. setproctitle() unaware application continue to see argv[0] directly.
>   it makes some inconsistent behavior. 
> 2. proc title (i.e. string) injection need to map new page as process title area.
>    implicit mapping increasing makes new trouble
>    - mihgt cause to exceed max_map_count awhile after.
>    - might cause leak proc title area (who know when it should be freed?)
> 
> I think reasonable way is 1. send signal (or use another inter process
> communication way) to target process 2. target process change own proc title
> themself.
> 
> Plus, I haven't seen the use-case of changin another task. iow I doubt
> it's worth to change lots code.

if your mention is strongly, can you please explain your expected use case?


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