linux-kernel - Re: [PATCH v2] net: arcnet: Fix a possible concurrency use-after-free bug in arcnet_reply

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Message-Id: <20181228.213103.793343860286706296.davem@davemloft.net>
Date:   Fri, 28 Dec 2018 21:31:03 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     baijiaju1990@...il.com
Cc:     m.grzeschik@...gutronix.de, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net: arcnet: Fix a possible concurrency
 use-after-free bug in arcnet_reply_tasklet()

From: Jia-Ju Bai <baijiaju1990@...il.com>
Date: Thu, 27 Dec 2018 10:01:42 +0800

> @@ -401,6 +401,7 @@ static void arcnet_reply_tasklet(unsigned long data)
>  	struct sock_exterr_skb *serr;
>  	struct sock *sk;
>  	int ret;
> +	unsigned long flags;
>  
>  	local_irq_disable();
>  	skb = lp->outgoing.skb;
> @@ -426,10 +427,14 @@ static void arcnet_reply_tasklet(unsigned long data)
>  	serr->ee.ee_data = skb_shinfo(skb)->tskey;
>  	serr->ee.ee_info = lp->reply_status;
>  
> +	spin_lock_irqsave(&lp->lock, flags);
> +
>  	/* finally erasing outgoing skb */
>  	dev_kfree_skb(lp->outgoing.skb);
>  	lp->outgoing.skb = NULL;
>  
> +	spin_unlock_irqrestore(&lp->lock, flags);
> +
>  	ackskb->dev = lp->dev;
>  
>  	ret = sock_queue_err_skb(sk, ackskb);

This is not the correct fix.

You need to instead replace the existing local_irq_*() calls in the
function with the spinlock stuff.