linux-kernel - Re: [RFC PATCH v3] audit: use proper refcount locking on audit

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Message-ID: <CAM_iQpVuzYRAb4qFj1kPduxCUsAjkyik=qXriQcP6g7gPgyXRQ@mail.gmail.com>
Date:   Tue, 13 Dec 2016 21:36:37 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>, linux-audit@...hat.com,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v3] audit: use proper refcount locking on audit_sock

On Tue, Dec 13, 2016 at 8:00 PM, Richard Guy Briggs <rgb@...hat.com> wrote:
> On 2016-12-13 16:19, Cong Wang wrote:
>> On Tue, Dec 13, 2016 at 7:03 AM, Richard Guy Briggs <rgb@...hat.com> wrote:
>> > @@ -1283,8 +1299,10 @@ static void __net_exit audit_net_exit(struct net *net)
>> >  {
>> >         struct audit_net *aunet = net_generic(net, audit_net_id);
>> >         struct sock *sock = aunet->nlsk;
>> > +       mutex_lock(&audit_cmd_mutex);
>> >         if (sock == audit_sock)
>> >                 auditd_reset();
>> > +       mutex_unlock(&audit_cmd_mutex);
>>
>> This still doesn't look correct to me, b/c here we release the audit_sock
>> refcnt twice:
>>
>> 1) inside audit_reset()
>
> The audit_reset() refcount decrement corresponds to a setting of
> audit_sock only if audit_sock is still non-NULL.
>

Hmm, thinking about it again, looks like the sock == audit_sock
and audit_sock != NULL checks can guarantee we are safe. So,

Reviewed-by: Cong Wang <xiyou.wangcong@...il.com>