linux-kernel - Re: [PATCH] unix: avoid use-after-free in ep_remove_wait

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Message-ID: <564F4458.8050309@akamai.com>
Date:	Fri, 20 Nov 2015 11:03:36 -0500
From:	Jason Baron <jbaron@...mai.com>
To:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
Cc:	Dmitry Vyukov <dvyukov@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Michal Kubecek <mkubecek@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	David Howells <dhowells@...hat.com>,
	Paul Moore <paul@...l-moore.com>, salyzyn@...roid.com,
	sds@...ho.nsa.gov, ying.xue@...driver.com,
	netdev <netdev@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Julien Tinnes <jln@...gle.com>,
	Kees Cook <keescook@...gle.com>,
	Mathias Krause <minipli@...glemail.com>
Subject: Re: [PATCH] unix: avoid use-after-free in ep_remove_wait_queue (w/
 Fixes:)

On 11/19/2015 06:52 PM, Rainer Weikusat wrote:

[...]

> @@ -1590,21 +1718,35 @@ restart:
>  			goto out_unlock;
>  	}
>  
> -	if (unix_peer(other) != sk && unix_recvq_full(other)) {
> -		if (!timeo) {
> +	if (unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {
> +		if (timeo) {
> +			timeo = unix_wait_for_peer(other, timeo);
> +
> +			err = sock_intr_errno(timeo);
> +			if (signal_pending(current))
> +				goto out_free;
> +
> +			goto restart;
> +		}
> +
> +		if (unix_peer(sk) != other ||
> +		    unix_dgram_peer_wake_me(sk, other)) {
>  			err = -EAGAIN;
>  			goto out_unlock;
>  		}

Hi,

So here we are calling unix_dgram_peer_wake_me() without the sk lock the first time
through - right? In that case, we can end up registering on the queue of other for
the callback but we might have already connected to a different remote. In that case,
the wakeup will crash if 'sk' has freed in the meantime.

Thanks,

-Jason

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