netdev - Re: [PATCH net] net/packet: fix a race in packet_bind() and packet

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Message-Id: <20171128.094855.1432729042351719024.davem@davemloft.net>
Date:   Tue, 28 Nov 2017 09:48:55 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     netdev@...r.kernel.org, fruggeri@...stanetworks.com,
        willemb@...gle.com
Subject: Re: [PATCH net] net/packet: fix a race in packet_bind() and
 packet_notifier()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 27 Nov 2017 20:00:52 -0800

> @@ -368,9 +368,11 @@ static void __unregister_prot_hook(struct sock *sk, bool sync)
>  	__sock_put(sk);
>  
>  	if (sync) {
> +		po->frozen = 1;
>  		spin_unlock(&po->bind_lock);
>  		synchronize_net();
>  		spin_lock(&po->bind_lock);
> +		po->frozen = 0;
>  	}
>  }
>  

Ugh.

Maybe you can just set po->num to zero in the bind code path which causes
this problem.  That will prevent this situation entirely.