netdev - Re: [PATCH net] packet: hold bind lock when rebinding to fanout hook

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Date:   Fri, 15 Sep 2017 10:07:46 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Willem de Bruijn <willemb@...gle.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        nixiaoming <nixiaoming@...wei.com>
Subject: Re: [PATCH net] packet: hold bind lock when rebinding to fanout hook

On Thu, Sep 14, 2017 at 5:14 PM, Willem de Bruijn <willemb@...gle.com> wrote:
> Packet socket bind operations must hold the po->bind_lock. This keeps
> po->running consistent with whether the socket is actually on a ptype
> list to receive packets.
>
> fanout_add unbinds a socket and its packet_rcv/tpacket_rcv call, then
> binds the fanout object to receive through packet_rcv_fanout.
>
> Make it hold the po->bind_lock when testing po->running and rebinding.
> Else, it can race with other rebind operations, such as that in
> packet_set_ring from packet_rcv to tpacket_rcv. Concurrent updates
> can result in a socket being added to a fanout group twice, causing
> use-after-free KASAN bug reports, among others.
>
> Reported independently by both trinity and syzkaller.
> Verified that the syzkaller reproducer passes after this patch.
>

I forgot to add the Fixes tag, sorry.

Fixes: dc99f600698d ("packet: Add fanout support.")

> Reported-by: nixioaming <nixiaoming@...wei.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>