linux-kernel - Re: net/packet: use-after-free in packet_rcv

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Date:   Fri, 10 Feb 2017 11:16:24 -0800
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        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,
        Philip Pettersson <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 (02/10/17 10:00), Cong Wang wrote:
> My understanding about the race here is packet_release() doesn't
> wait for flying packets correctly, which leads to a flying packet still
> refers to the struct sock which is being released.
> 
> This could happen because struct packet_fanout is refcn'ted, it is
   :
> At least I believe this explains the crash Dmitry reported.

hmm, the proof of the pudding is in the eating- would be good to 
be able to reliably reproduce this somewhere (thus proving that
root-cause analysis is rock-solid), maybe by introducing artificial
delays to slow down paths..

I'm travelling at the moment but may be able to give this (try
to reproduce it reliably) next week.

--Sowmini