netdev - Re: use-after-free in sctp_do

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Message-ID: <1449175884.17296.2.camel@perches.com>
Date:	Thu, 03 Dec 2015 12:51:24 -0800
From:	Joe Perches <joe@...ches.com>
To:	Jason Baron <jbaron@...mai.com>, Aaron Conole <aconole@...hat.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Vladislav Yasevich <vyasevich@...il.com>,
	linux-sctp@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in sctp_do_sm

(adding lkml as this is likely better discussed there)

On Thu, 2015-12-03 at 15:42 -0500, Jason Baron wrote:
> On 12/03/2015 03:24 PM, Joe Perches wrote:
> > On Thu, 2015-12-03 at 15:10 -0500, Jason Baron wrote:
> > > On 12/03/2015 03:03 PM, Joe Perches wrote:
> > > > On Thu, 2015-12-03 at 14:32 -0500, Jason Baron wrote:
> > > > > On 12/03/2015 01:52 PM, Aaron Conole wrote:
> > > > > > I think that as a minimum, the following patch should be evaluted,
> > > > > > but am unsure to whom I should submit it (after I test):
> > > > []
> > > > > Agreed - the intention here is certainly to have no side effects. It
> > > > > looks like 'no_printk()' is used in quite a few other places that would
> > > > > benefit from this change. So we probably want a generic
> > > > > 'really_no_printk()' macro.
> > > > 
> > > > https://lkml.org/lkml/2012/6/17/231
> > > 
> > > I don't see this in the tree.
> > 
> > It never got applied.
> > 
> > > Also maybe we should just convert
> > > no_printk() to do what your 'eliminated_printk()'.
> > 
> > Some of them at least.
> > 
> > > So we can convert all users with this change?
> > 
> > I don't think so, I think there are some
> > function evaluation/side effects that are
> > required.  I believe some do hardware I/O.
> > 
> > It'd be good to at least isolate them.
> > 
> > I'm not sure how to find them via some
> > automated tool/mechanism though.
> > 
> > I asked Julia Lawall about it once in this
> > thread:  https://lkml.org/lkml/2014/12/3/696
> > 
> 
> Seems rather fragile to have side effects that we rely
> upon hidden in a printk().

Yup.

> Just convert them and see what breaks :)

I appreciate your optimism.  It's very 1995.
Try it and see what happens.

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