netdev - Re: [PATCH v2 1/3] unix: fix use-after-free in unix_dgram

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Date:	Mon, 05 Oct 2015 09:54:34 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
Cc:	Jason Baron <jbaron@...mai.com>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	minipli@...glemail.com, normalperson@...t.net,
	viro@...iv.linux.org.uk, davidel@...ilserver.org,
	dave@...olabs.net, olivier@...ras.ch, pageexec@...email.hu,
	torvalds@...ux-foundation.org, peterz@...radead.org
Subject: Re: [PATCH v2 1/3] unix: fix use-after-free in unix_dgram_poll()

On Mon, 2015-10-05 at 17:31 +0100, Rainer Weikusat wrote:

>  	atomic_long_set(&u->inflight, 0);
>  	INIT_LIST_HEAD(&u->link);
> @@ -2135,8 +2139,16 @@ static unsigned int unix_poll(struct fil
>  static unsigned int unix_dgram_poll(struct file *file, struct socket *sock,
>  				    poll_table *wait)
>  {
> -	struct sock *sk = sock->sk, *other;
> -	unsigned int mask, writable;
> +	struct sock *sk = sock->sk, *other, *pp;
> +	struct unix_sock *u;
> +	unsigned int mask, writable, dead;
> +
> +	u = unix_sk(sk);
> +	pp = u->poll_peer;
> +	if (pp) {
> +		u->poll_peer = NULL;
> +		sock_put(pp);
> +	}


This looks racy.
Multiple threads could use poll() at the same time,
and you would have too many sock_put()



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