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From:   Josh Elsasser <jelsasser@appneta.com>
Date:   Mon, 12 Mar 2018 22:17:58 -0700
Message-ID: <CAFKWs58UYJzM+ei7HLUPWW1-78OaQ=faBs7tjSipYGgETcsrAQ@mail.gmail.com>
Subject: Re: [PATCH 1/1] net: check dev->reg_state before deref of napi netdev_ops
To:     Cong Wang <xiyou.wangcong@gmail.com>
Cc:     David Miller <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Eric Dumazet <edumazet@google.com>,
        Sasha Levin <alexander.levin@verizon.com>,
        Willem de Bruijn <willemb@google.com>,
        Alexander Potapenko <glider@google.com>,
        =?UTF-8?Q?Michal_Kube=C4=8Dek?= <mkubecek@suse.cz>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Mar 12, 2018 at 4:17 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> On Sun, Mar 11, 2018 at 12:22 PM, Josh Elsasser <jelsasser@appneta.com> wrote:
>> init_dummy_netdev() leaves its netdev_ops pointer zeroed. This leads
>> to a NULL pointer dereference when sk_busy_loop fires against an iwlwifi
>> wireless adapter and checks napi->dev->netdev_ops->ndo_busy_poll.
>>
>> Avoid this by ensuring that napi->dev is not a dummy device before
>> dereferencing napi dev's netdev_ops, preventing the following panic:
>
> Hmm, how about just checking ->netdev_ops? Checking reg_state looks
> odd, although works.

Fair point. I was trying to differentiate between an unexpected
NULL pointer and a dummy netdev, but I guess it was clever
at the expense of readability.

I'll push up a v2 that just does the obvious.