From: Joe Perches <joe@perches.com>
Date: Thu, 03 Dec 2015 20:51:24 +0000
Subject: Re: use-after-free in sctp_do_sm
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To: Jason Baron <jbaron@akamai.com>, Aaron Conole <aconole@redhat.com>, Dmitry Vyukov <dvyukov@google.com>, Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>
Cc: Eric Dumazet <edumazet@google.com>, syzkaller <syzkaller@googlegroups.com>, Vladislav Yasevich <vyasevich@gmail.com>, linux-sctp@vger.kernel.org, netdev <netdev@vger.kernel.org>, Kostya Serebryany <kcc@google.com>, Alexander Potapenko <glider@google.com>, Sasha Levin <sasha.levin@oracle.com>

(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 evalut=
ed,
> > > > > > 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.
> > > >=20
> > > > https://lkml.org/lkml/2012/6/17/231
> > >=20
> > > I don't see this in the tree.
> >=20
> > It never got applied.
> >=20
> > > Also maybe we should just convert
> > > no_printk() to do what your 'eliminated_printk()'.
> >=20
> > Some of them at least.
> >=20
> > > So we can convert all users with this change?
> >=20
> > I don't think so, I think there are some
> > function evaluation/side effects that are
> > required.=A0=A0I believe some do hardware I/O.
> >=20
> > It'd be good to at least isolate them.
> >=20
> > I'm not sure how to find them via some
> > automated tool/mechanism though.
> >=20
> > I asked Julia Lawall about it once in this
> > thread:=A0=A0https://lkml.org/lkml/2014/12/3/696
> >=20
>=20
> 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. =A0It's very 1995.
Try it and see what happens.