linux-kernel - Re: [PATCH net] kcm: Fix kernel NULL pointer dereference in requeue_rx

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Date:   Mon, 14 Nov 2022 09:24:10 +0800
From:   "wanghai (M)" <wanghai38@...wei.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <cong.wang@...edance.com>,
        <f.fainelli@...il.com>, <tom@...bertland.com>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net] kcm: Fix kernel NULL pointer dereference in
 requeue_rx_msgs


在 2022/11/14 8:55, Cong Wang 写道:
> On Sat, Nov 12, 2022 at 08:04:23PM +0800, Wang Hai wrote:
>> In kcm_rcv_strparser(), the skb is queued to the kcm that is currently
>> being reserved, and if the queue is full, unreserve_rx_kcm() will be
>> called. At this point, if KCM_RECV_DISABLE is set, then unreserve_rx_kcm()
>> will requeue received messages for the current kcm socket to other kcm
>> sockets. The kcm sock lock is not held during this time, and as long as
>> someone calls kcm_recvmsg, it will concurrently unlink the same skb, which
>> ill result in a null pointer reference.
>>
>> cpu0 			cpu1		        cpu2
>> kcm_rcv_strparser
>>   reserve_rx_kcm
>>                          kcm_setsockopt
>>                           kcm_recv_disable
>>                            kcm->rx_disabled = 1;
>>    kcm_queue_rcv_skb
>>    unreserve_rx_kcm
>>     requeue_rx_msgs                              kcm_recvmsg
>>      __skb_dequeue
>>       __skb_unlink(skb)				  skb_unlink(skb)
>>                                                    //double unlink skb
>>
> We will hold skb queue lock after my patch, so this will not happen after
> applying my patch below?
> https://lore.kernel.org/netdev/20221114005119.597905-1-xiyou.wangcong@gmail.com/

Hi Cong,

I tested your patch and it fixed my problem, thanks.

> .

-- 
Wang Hai