linux-kernel - Re: af_packet: use after free in prb_retire_rx_blk_timer

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Date:   Sun, 23 Jul 2017 10:03:32 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     "liujian (CE)" <liujian56@...wei.com>
Cc:     Dingtianhong <dingtianhong@...wei.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Dave Jones <davej@...emonkey.org.uk>,
        "alexander.levin@...izon.com" <alexander.levin@...izon.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "willemb@...gle.com" <willemb@...gle.com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: af_packet: use after free in prb_retire_rx_blk_timer_expired

On Sun, Jul 23, 2017 at 5:48 AM, liujian (CE) <liujian56@...wei.com> wrote:
> Hi
>
> I find it caused by below steps:
> 1. set tp_version to TPACKET_V3 and req->tp_block_nr to 1
> 2. set tp_block_nr to 0
> Then pg_vec was freed, and we did not delete the timer?

Thanks for testing!

Ah, I overlook the initialization case in my previous patch.

How about the following one? Does it cover all the cases?


diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 008bb34ee324..0615c2a950fa 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -4329,7 +4329,7 @@ static int packet_set_ring(struct sock *sk,
union tpacket_req_u *req_u,
                register_prot_hook(sk);
        }
        spin_unlock(&po->bind_lock);
-       if (closing && (po->tp_version > TPACKET_V2)) {
+       if (pg_vec && (po->tp_version > TPACKET_V2)) {
                /* Because we don't support block-based V3 on tx-ring */
                if (!tx_ring)
                        prb_shutdown_retire_blk_timer(po, rb_queue);