linux-kernel - Re: [PATCH] net: usb: r8152: Check used MAC passthrough address

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Date:   Wed, 5 Jan 2022 11:55:06 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Aaron Ma <aaron.ma@...onical.com>,
        Henning Schild <henning.schild@...mens.com>
Cc:     kuba@...nel.org, linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, davem@...emloft.net,
        hayeswang@...ltek.com, tiwai@...e.de
Subject: Re: [PATCH] net: usb: r8152: Check used MAC passthrough address

On 1/5/22 12:37 AM, Aaron Ma wrote:
> 
> 
> On 1/5/22 16:32, Henning Schild wrote:
>> Am Wed, 5 Jan 2022 16:01:24 +0800
>> schrieb Aaron Ma <aaron.ma@...onical.com>:
>>
>>> On 1/5/22 15:55, Henning Schild wrote:
>>>> Am Wed, 5 Jan 2022 15:38:51 +0800
>>>> schrieb Aaron Ma <aaron.ma@...onical.com>:
>>>>   
>>>>> On 1/5/22 15:32, Henning Schild wrote:
>>>>>> Am Wed, 5 Jan 2022 08:23:55 +0100
>>>>>> schrieb Henning Schild <henning.schild@...mens.com>:
>>>>>>      
>>>>>>> Hi Aaron,
>>>>>>>
>>>>>>> if this or something similar goes in, please add another patch to
>>>>>>> remove the left-over defines.
>>>>>>>      
>>>>>
>>>>> Sure, I will do it.
>>>>>  
>>>>>>> Am Wed,  5 Jan 2022 14:17:47 +0800
>>>>>>> schrieb Aaron Ma <aaron.ma@...onical.com>:
>>>>>>>     
>>>>>>>> When plugin multiple r8152 ethernet dongles to Lenovo Docks
>>>>>>>> or USB hub, MAC passthrough address from BIOS should be
>>>>>>>> checked if it had been used to avoid using on other dongles.
>>>>>>>>
>>>>>>>> Currently builtin r8152 on Dock still can't be identified.
>>>>>>>> First detected r8152 will use the MAC passthrough address.
>>>>>>>>
>>>>>>>> Signed-off-by: Aaron Ma <aaron.ma@...onical.com>
>>>>>>>> ---
>>>>>>>>     drivers/net/usb/r8152.c | 10 ++++++++++
>>>>>>>>     1 file changed, 10 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
>>>>>>>> index f9877a3e83ac..77f11b3f847b 100644
>>>>>>>> --- a/drivers/net/usb/r8152.c
>>>>>>>> +++ b/drivers/net/usb/r8152.c
>>>>>>>> @@ -1605,6 +1605,7 @@ static int
>>>>>>>> vendor_mac_passthru_addr_read(struct r8152 *tp, struct sockaddr
>>>>>>>> *sa) char *mac_obj_name; acpi_object_type mac_obj_type;
>>>>>>>>         int mac_strlen;
>>>>>>>> +    struct net_device *ndev;
>>>>>>>>             if (tp->lenovo_macpassthru) {
>>>>>>>>             mac_obj_name = "\\MACA";
>>>>>>>> @@ -1662,6 +1663,15 @@ static int
>>>>>>>> vendor_mac_passthru_addr_read(struct r8152 *tp, struct sockaddr
>>>>>>>> *sa) ret = -EINVAL; goto amacout;
>>>>>>>>         }
>>>>>>>> +    rcu_read_lock();
>>>>>>>> +    for_each_netdev_rcu(&init_net, ndev) {
>>>>>>>> +        if (strncmp(buf, ndev->dev_addr, 6) == 0) {
>>>>>>>> +            rcu_read_unlock();
>>>>>>>> +            goto amacout;
>>>>>>>
>>>>>>> Since the original PCI netdev will always be there, that would
>>>>>>> disable inheritance would it not?
>>>>>>> I guess a strncmp(MODULE_NAME, info->driver, strlen(MODULE_NAME))
>>>>>>> is needed as well.
>>>>>>>      
>>>>>
>>>>> PCI ethernet could be a builtin one on dock since there will be
>>>>> TBT4 dock.
>>>>
>>>> In my X280 there is a PCI device in the laptop, always there. And
>>>> its MAC is the one found in ACPI. Did not try but i think for such
>>>> devices there would never be inheritance even if one wanted and
>>>> used a Lenovo dock that is supposed to do it.
>>>>    
>>>
>>> There will more TBT4 docks in market, the new ethernet is just the
>>> same as PCI device, connected by thunderbolt.
>>>
>>> For exmaple, connect a TBT4 dock which uses i225 pcie base ethernet,
>>> then connect another TBT3 dock which uses r8152.
>>> If skip PCI check, then i225 and r8152 will use the same MAC.
>>
>> In current 5.15 i have that sort of collision already. All r8152s will
>> happily grab the MAC of the I219. In fact i have only ever seen it with
>> one r8152 at a time but while the I219 was actively in use.
>> While this patch will probably solve that, i bet it would defeat MAC
>> pass-thru altogether. Even when turned on in the BIOS.
>> Or does that iterator take "up"/"down" state into consideration? But
>> even if, the I219 could become "up" any time later.
>>
> 
> No, that's different, I219 got MAC from their own space.
> MAC passthrough got MAC from ACPI "\MACA".
> 
>> These collisions are simply bound to happen and probably very hard to
>> avoid once you have set your mind on allowing pass-thru in the first
>> place. Not sure whether that even has potential to disturb network
>> equipment like switches.
>>
> 
> After check MAC address, it will be more safe.

Sorry to just do a drive by review here, but why is passing through the
MAC a kernel problem and not something that you punt to user-space entirely?
-- 
Florian