linux-kernel - Re: [PATCH] can: Fix kernel panic at security_sock_rcv

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Message-ID: <6dc1d111-9aa4-5771-0283-6408567e47c2@hartkopp.net>
Date:   Sat, 14 Jan 2017 14:53:42 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Liu Shuo <shuo.a.liu@...el.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     linux-kernel@...r.kernel.org, yanmin_zhang@...ux.intel.com,
        shuox.liu@...il.com, Zhang Yanmin <yanmin.zhang@...el.com>,
        "He, Bo" <bo.he@...el.com>, Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:CAN NETWORK LAYER" <linux-can@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>
Subject: Re: [PATCH] can: Fix kernel panic at security_sock_rcv_skb

Hello Eric,

On 01/14/2017 04:43 AM, Liu Shuo wrote:
> On Thu 12.Jan'17 at 17:33:38 +0100, Oliver Hartkopp wrote:
>> On 01/12/2017 02:01 PM, Eric Dumazet wrote:

>>> The main problem seems that the sockets themselves are not RCU
>>> protected.
>>>
>>> If CAN uses RCU for delivery, then sockets should be freed only after
>>> one RCU grace period.
>>>
>>> On recent kernels, following patch could help :
>>>
>>
>> Thanks Eric!
>>
>> @Liu ShuoX: Can you check if Eric's suggestion fixes the issue in your
>> setup?
> Sorry for late reply. I was OOO yesterday.
> With Eric's hint, i just found his patch that "net: add SOCK_RCU_FREE
> socket flag" in the latest kernel. With backporting this one plus Eric's
> following patch, it fixs my failure.

what would be the best approach to fix this issue - even in stable kernels?

E.g. would this change be ok for a stable as a quick fix?

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 1108079d934f..6b974c2b66ef 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -112,6 +112,7 @@ EXPORT_SYMBOL(can_ioctl);

  static void can_sock_destruct(struct sock *sk)
  {
+       synchronize_rcu();
         skb_queue_purge(&sk->sk_receive_queue);
  }

And once this arrived in the mainline tree your suggested patch could be 
applied?

In any case we should not forget to give Reported-by credits to Liu.

Best regards,
Oliver