linux-kernel - Re: Re: [PATCH] net/packet: fix race condition between fanout_add and __unregister_prot

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Date:   Tue, 19 Sep 2017 12:09:55 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Nixiaoming <nixiaoming@...wei.com>
Cc:     "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH] net/packet: fix race condition between fanout_add and __unregister_prot_hook

On Tue, Sep 19, 2017 at 3:21 AM, Nixiaoming <nixiaoming@...wei.com> wrote:
> On Fri, Sep 15, 2017 at 10:46 AM, Willem de Bruijn
>
> <willemdebruijn.kernel@...il.com> wrote:
>
>>
>
>> In case of failure we also need to unlink and free match. I
>
>> sent the following:
>
>>
>
>> http://patchwork.ozlabs.org/patch/813945/
>
>
>
> +       spin_lock(&po->bind_lock);
>
> +       if (po->running &&
>
> +           match->type == type &&
>
>            match->prot_hook.type == po->prot_hook.type &&
>
>            match->prot_hook.dev == po->prot_hook.dev) {
>
>                 err = -ENOSPC;
>
> @@ -1761,6 +1760,13 @@  static int fanout_add(struct sock *sk, u16 id, u16
> type_flags)
>
>                           err = 0;
>
>                 }
>
>        }
>
> +       spin_unlock(&po->bind_lock);
>
> +
>
> +       if (err && !refcount_read(&match->sk_ref)) {
>
> +                list_del(&match->list);
>
> +                kfree(match);
>
> +       }
>
>
>
>
>
> In the function fanout_add add spin_lock to protect po-> running and po->
> fanout,
>
> then whether it should be in the function fanout_release also add spin_lock
> protection ?

po->bind_lock is held when registering and unregistering the
protocol hook. fanout_release does access po->running or
prot_hook.

It is called from packet_release, which does hold the bind_lock
when unregistering the protocol hook.