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

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Message-ID: <1486749763.7793.152.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Fri, 10 Feb 2017 10:02:43 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Anoob Soman <anoob.soman@...rix.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 Fri, 2017-02-10 at 09:59 -0800, Eric Dumazet wrote:
> On Fri, 2017-02-10 at 09:49 -0800, Cong Wang wrote:
> > 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.
> 
> Fine. But your patch makes absolutely no sense.

At least, Anoob patch is making a step into the right direction ;)

https://patchwork.ozlabs.org/patch/726532/