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

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Date:	Tue, 14 Dec 2010 17:03:13 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	"Suzuki K. Poulose" <suzuki@...ibm.com>,
	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

Hello,

On 12/14/2010 04:49 PM, Linus Torvalds 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?

I think a better way would be adding a ptrace attach which is nestable
and doesn't have the nasty side effect caused by the interactions
between the implicit SIGSTOP and group stop.  As a preparation step, I
posted a patchset to cleanup the interactions between ptrace and group
stop which is being reviewed.  Once we have a nestable ptrace attach,
we should be able to simply adapt gcore(1) to use it and write out
core dump from userland.

Thanks.

-- 
tejun
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