linux-kernel - Re: use-after-free in sock_wake

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Message-Id: <1448558149.915134.450891745.0035D750@webmail.messagingengine.com>
Date:	Thu, 26 Nov 2015 18:15:49 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Rainer Weikusat <rweikusat@...ileactivedefense.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Benjamin LaHaise <bcrl@...ck.org>,
	"David S. Miller" <davem@...emloft.net>,
	Al Viro <viro@...iv.linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Ying Xue <ying.xue@...driver.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in sock_wake_async

On Thu, Nov 26, 2015, at 18:09, Eric Dumazet wrote:
> On Thu, 2015-11-26 at 18:03 +0100, Hannes Frederic Sowa wrote:
> 
> > My rationale was like this: we already have rcu to free the wq, so we
> > don't add any more callbacks as current code. sock_alloc is right now
> > 1136 bytes, which is huge, like 18 cachelines. I wouldn't think it does
> > matter a lot as we thrash anyway. tcp_sock is like 45 cachelines right
> > now, hui.
> 
> Again, these speculations are really killing me.
>
> Can you wait I send my patches ?

Eric, I wasn't targeting upstream. I just had this idea and wanted to
show you that it is possible. I didn't send an official patch and
wouldn't do that without proper performance analysis.

> They work just great, and there is no risk of perf regression with added
> RCU freeing of inodes :(

I agree. Your patch is certainly the best thing for net while this
complete rcuification should never ever hit net.

> It is Thanks Giving in the US, vacation time.

Enjoy the time! :)

Bye,
Hannes
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