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

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Date:   Thu, 9 Feb 2017 07:17:09 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...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 Thu, Feb 9, 2017 at 7:12 AM, Sowmini Varadhan
<sowmini.varadhan@...cle.com> wrote:
> On (02/09/17 14:14), Dmitry Vyukov wrote:
>>
>> Call Trace:
>    :
>>  packet_rcv_has_room+0x25/0xb0 net/packet/af_packet.c:1308
>>  fanout_demux_rollover+0x3bb/0x6b0 net/packet/af_packet.c:1388
>>  packet_rcv_fanout+0x674/0x800 net/packet/af_packet.c:1490
>>  dev_queue_xmit_nit+0x73a/0xa90 net/core/dev.c:1898
>     :
>>  tcp_sendmsg_fastopen net/ipv4/tcp.c:1110 [inline]
>     :
>
> looks like a race between a NIT socket (tcpdump, maybe?) that is closing,
> and a standard tcp socket.. packet_release() takes the po->bind_lock
> to remove the socket from the ptype_all NIT queue. but how does
> that sync with the Tx path for other af_inet/af_inet6 sockets?

RCU protection for hooks.