linux-kernel - Re: [RFC] [Patch 0/21] Non disruptive application core dump infrastructure

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Message-ID: <20101215110446.157bbb25@suzukikp>
Date:	Wed, 15 Dec 2010 11:04:46 +0530
From:	"Suzuki K. Poulose" <suzuki@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Christoph Hellwig <hch@....de>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Daisuke HATAYAMA <d.hatayama@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Roland McGrath <roland@...hat.com>,
	Amerigo Wang <amwang@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] [Patch 0/21] Non disruptive application core dump
 infrastructure

On Tue, 14 Dec 2010 07:49:37 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Tue, Dec 14, 2010 at 1:52 AM, Suzuki K. Poulose <suzuki@...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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