netdev - Re: [PATCH]: Add Network Sysrq Support

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Message-ID: <20110622105434.GE16021@Chamillionaire.breakpoint.cc>
Date:	Wed, 22 Jun 2011 12:54:34 +0200
From:	Florian Westphal <fw@...len.de>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	David Miller <davem@...emloft.net>, fbl@...hat.com,
	netdev@...r.kernel.org, agospoda@...hat.com, nhorman@...hat.com,
	lwoodman@...hat.com, john.haxby@...cle.com
Subject: Re: [PATCH]: Add Network Sysrq Support

Prarit Bhargava <prarit@...hat.com> wrote:

[ cc'd John Haxby, who worked on xt_SYSREQ ]

> On 06/21/2011 06:58 PM, David Miller wrote:
> > From: Florian Westphal <fw@...len.de>
> > Date: Wed, 22 Jun 2011 00:56:45 +0200
> >> This is one of the reasons why I still think that
> >> xt_SYSREQ would be the better solution, you get all
> >> kinds of filtering features for free.
> >>
> >> You could even use crazy things like '-m time' to restrict
> >> sysreq availability to working hours and whatnot.
> >>
> > Agreed.
> Using the netfilter xt-SYSRQ code seems to store the entered code and
> execute it later after the system has returned to a normal state....
> which is much too late to be useful.

The target handler of the kernel part invokes handle_sysrq(),
I don't see any delaying/queueing?

FWIW, the old discussion is in the archives:
search for subject "nf-next: sysrq and condition 20100421" from Jan
Engelhardt, or try
http://thread.gmane.org/gmane.comp.security.firewalls.netfilter.devel/33615/focus=34808

As far as i understand the use case described by John Haxby matches yours.

Patrick McHardy suggested an alternative standalone method involving
encapsulation sockets; perhaps the reasons why this path was not chosen
have changed.

I think that a standalone module (i.e. not requiring netfilter) that
runs the sysreq handling after all netfilter hooks would be optimal,
but I don't see a simple method to implement that.
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