netdev - Re: net/packet: use-after-free in packet_rcv

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Message-ID: <CAM_iQpXHktH+Wo7GtJC4afY_Wm11PpKcNFx41f_x4Vs93J-bMA@mail.gmail.com>
Date:   Fri, 10 Feb 2017 09:49:31 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>, jarno@....org,
        Sowmini Varadhan <sowmini.varadhan@...cle.com>,
        philip.pettersson@...il.com, weongyo.linux@...il.com,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/packet: use-after-free in packet_rcv_fanout

On Thu, Feb 9, 2017 at 7:23 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2017-02-09 at 19:19 -0800, Eric Dumazet wrote:
>
>> More likely the bug is in fanout_add(), with a buggy sequence in error
>> case, and not correct locking.
>>
>> kfree(po->rollover);
>> po->rollover = NULL;
>>
>> Two cpus entering fanout_add() (using the same af_packet socket,
>> syzkaller courtesy...) might both see po->fanout being NULL.
>>
>> Then they grab the mutex.  Too late...
>
> Patch could be :
>

For me, clearly the data structure that use-after-free'd is struct sock
rather than struct packet_rollover.