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

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Date:	Wed, 25 Nov 2015 09:51:31 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Benjamin LaHaise <bcrl@...ck.org>,
	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	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 Wed, 2015-11-25 at 17:30 +0000, Rainer Weikusat wrote:

> In case this is wrong, it obviously implies that sk_sleep(sk) must not
> be used anywhere as it accesses the same struck sock, hence, when that
> can "suddenly" disappear despite locks are used in the way indicated
> above, there is now safe way to invoke that, either, as it just does a
> rcu_dereference_raw based on the assumption that the caller knows that
> the i-node (and the corresponding wait queue) still exist.
> 

Oh well.

sk_sleep() is not used if the return is NULL

This is exactly why we have such code in critical functions :

wqueue = sk_sleep(sk);
if (wqueue && waitqueue_active(wqueue))
	wake_up_interruptible_poll(wqueue, 
				   POLLOUT | POLLWRNORM | POLLWRBAND);


We already took care of this problem years ago, but missed the ASYNC
case (that almost nobody really uses these days)



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