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Date:   Fri, 28 Oct 2022 15:50:15 +0800
From:   shaozhengchao <shaozhengchao@...wei.com>
To:     Oliver Hartkopp <socketcan@...tkopp.net>,
        <linux-can@...r.kernel.org>, <netdev@...r.kernel.org>,
        <mkl@...gutronix.de>, <davem@...emloft.net>, <edumazet@...gle.com>,
        <kuba@...nel.org>, <pabeni@...hat.com>
CC:     <linux@...pel-privat.de>, <weiyongjun1@...wei.com>,
        <yuehaibing@...wei.com>
Subject: Re: [PATCH net] can: af_can: fix NULL pointer dereference in
 can_rx_register()



On 2022/10/28 15:13, Oliver Hartkopp wrote:
> Hello,
> 
> On 28.10.22 05:33, Zhengchao Shao wrote:
>> It causes NULL pointer dereference when testing as following:
>> (a) use syscall(__NR_socket, 0x10ul, 3ul, 0) to create netlink socket.
>> (b) use syscall(__NR_sendmsg, ...) to create bond link device and vxcan
>>      link device, and bind vxcan device to bond device (can also use
>>      ifenslave command to bind vxcan device to bond device).
>> (c) use syscall(__NR_socket, 0x1dul, 3ul, 1) to create CAN socket.
>> (d) use syscall(__NR_bind, ...) to bind the bond device to CAN socket.
>>
>> The bond device invokes the can-raw protocol registration interface to
>> receive CAN packets. However, ml_priv is not allocated to the dev,
>> dev_rcv_lists is assigned to NULL in can_rx_register(). In this case,
>> it will occur the NULL pointer dereference issue.
> 
> I can see the problem and see that the patch makes sense for 
> can_rx_register().
> 
> But for me the problem seems to be located in the bonding device.
> 
> A CAN interface with dev->type == ARPHRD_CAN *always* has the 
> dev->ml_priv and dev->ml_priv_type set correctly.
> 
> I'm not sure if a bonding device does the right thing by just 'claiming' 
> to be a CAN device (by setting dev->type to ARPHRD_CAN) but not taking 
> care of being a CAN device and taking care of ml_priv specifics.
> 
> This might also be the case in other ml_priv use cases.
> 
> Would it probably make sense to blacklist CAN devices in bonding devices?
> 
> Thanks & best regards,
> Oliver
> 

Hi Oliver:
	Thank you for your review. The bond device inherits the type of
the slave device, but the bond device does not allocate ml_priv. I can
try to add ARPHRD_CAN to the blocklist of slave_dev. But I was
wondering, could there be other scenes with the same problem?

Zhengchao Shao
>>
>> The following is the stack information:
>> BUG: kernel NULL pointer dereference, address: 0000000000000008
>> PGD 122a4067 P4D 122a4067 PUD 1223c067 PMD 0
>> Oops: 0000 [#1] PREEMPT SMP
>> RIP: 0010:can_rx_register+0x12d/0x1e0
>> Call Trace:
>> <TASK>
>> raw_enable_filters+0x8d/0x120
>> raw_enable_allfilters+0x3b/0x130
>> raw_bind+0x118/0x4f0
>> __sys_bind+0x163/0x1a0
>> __x64_sys_bind+0x1e/0x30
>> do_syscall_64+0x35/0x80
>> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>> </TASK>
>>
>> Fixes: 4e096a18867a ("net: introduce CAN specific pointer in the 
>> struct net_device")
>> Signed-off-by: Zhengchao Shao <shaozhengchao@...wei.com>
>> ---
>>   net/can/af_can.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/can/af_can.c b/net/can/af_can.c
>> index 9503ab10f9b8..ef2697f3ebcb 100644
>> --- a/net/can/af_can.c
>> +++ b/net/can/af_can.c
>> @@ -450,7 +450,7 @@ int can_rx_register(struct net *net, struct 
>> net_device *dev, canid_t can_id,
>>       /* insert new receiver  (dev,canid,mask) -> (func,data) */
>> -    if (dev && dev->type != ARPHRD_CAN)
>> +    if (dev && (dev->type != ARPHRD_CAN || dev->ml_priv_type != 
>> ML_PRIV_CAN))
>>           return -ENODEV;
>>       if (dev && !net_eq(net, dev_net(dev)))

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