Date: Wed, 15 Dec 2010 11:04:46 +0530
From: "Suzuki K. Poulose" <suzuki@in.ibm.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Christoph Hellwig <hch@lst.de>, Masami Hiramatsu <mhiramat@redhat.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Daisuke HATAYAMA <d.hatayama@jp.fujitsu.com>,
        Andi Kleen <andi@firstfloor.org>, Roland McGrath <roland@redhat.com>,
        Amerigo Wang <amwang@redhat.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC] [Patch 0/21] Non disruptive application core dump
 infrastructure
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On Tue, 14 Dec 2010 07:49:37 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Tue, Dec 14, 2010 at 1:52 AM, Suzuki K. Poulose <suzuki@in.ibm.com> wrote:
> >
> > This is series of patches implementing an infrastructure for capturing the core
> > of an application without disrupting its process semantics.
> >
> > The infrastructure makes use of the freezer subsystem in kernel to freeze the
> > threads and then collect the information to generate ?the core.
> 
> This seems to be a fundamentally flawed approach.
> 
> From a security standpoint, it looks like a total disaster. A frozen
> process is really hard to get rid of, so it looks like an obvious DoS
> attack to just create lots of processes, then sneakily freeze them
> all, and then laugh at the poor system admin who has no idea what's
> going on. While frozen, the things are basically unkillable but look
> entirely normal, no?

You are right. We need a simple mechanism to hold the threads, so that we 
could collect the register information of the process without affecting its 
process semantics (eg, signals etc.). The suggestion by Kamezawa-san -a 
freeze state variant which allows SIGKILL - is one possibility.

I'd be very glad not using the freezer if there is a neat way to accomplish 
this without the undesired side effects. Tejun's ptrace enhancement would 
still require a userland program to control it(gcore); something contained 
in the kernel would be ideal.


Thanks

Suzuki

> 
>                                      Linus

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