netdev - Re: use-after-free in sctp_do

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Date:	Thu, 3 Dec 2015 14:15:13 -0200
From:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
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

On Thu, Dec 03, 2015 at 04:55:44PM +0100, Dmitry Vyukov wrote:
> On Thu, Dec 3, 2015 at 3:48 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> >>
> >> No, I don't. But pr_debug always computes its arguments. See no_printk
> >> in printk.h. So this use-after-free happens for all users.
> >
> > Hmm.
> >
> > pr_debug() should be a nop unless either DEBUG or CONFIG_DYNAMIC_DEBUG are set
> >
> > On our production kernels, pr_debug() is a nop.
> >
> > Can you double check ? Thanks !
> 
> 
> Why should it be nop? no_printk thing in printk.h pretty much
> explicitly makes it not a nop...
> 
> Double-checked: debug_post_sfx leads to some generated code:

Oups. I was under that impression too, that it would do sanity-check
while being optimized out.

I'll think on a fix for this.

Thanks,
  Marcelo

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