netdev - Re: [PATCH net-next v2 1/3] net: add check for current MAC address in dev_set_mac

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Date: Tue, 20 Jun 2023 13:42:14 +0300
From: Gal Pressman <gal@...dia.com>
To: Piotr Gardocki <piotrx.gardocki@...el.com>, netdev@...r.kernel.org
Cc: intel-wired-lan@...ts.osuosl.org, przemyslaw.kitszel@...el.com,
 michal.swiatkowski@...ux.intel.com, pmenzel@...gen.mpg.de, kuba@...nel.org,
 maciej.fijalkowski@...el.com, anthony.l.nguyen@...el.com,
 simon.horman@...igine.com, aleksander.lobakin@...el.com
Subject: Re: [PATCH net-next v2 1/3] net: add check for current MAC address in
 dev_set_mac_address

On 20/06/2023 13:29, Piotr Gardocki wrote:
> On 20.06.2023 09:16, Gal Pressman wrote:
>> On 13/06/2023 15:24, Piotr Gardocki wrote:
>>> In some cases it is possible for kernel to come with request
>>> to change primary MAC address to the address that is already
>>> set on the given interface.
>>>
>>> This patch adds proper check to return fast from the function
>>> in these cases.
>>>
>>> An example of such case is adding an interface to bonding
>>> channel in balance-alb mode:
>>> modprobe bonding mode=balance-alb miimon=100 max_bonds=1
>>> ip link set bond0 up
>>> ifenslave bond0 <eth>
>>>
>>> Signed-off-by: Piotr Gardocki <piotrx.gardocki@...el.com>
>>
>> Hello Piotr,
>>
>> I believe this patch has an (unintended?) side effect.
>> The early return in dev_set_mac_address() makes it so
>> 'dev->addr_assign_type' doesn't get assigned with NET_ADDR_SET, I don't
>> think this is the correct behavior.
> 
> Hi Gal,
> 
> I checked it, you're right. When the addr_assign_type is PERM or RANDOM
> and user or some driver sets the same MAC address the type doesn't change
> to NET_ADDR_SET. In my testing I didn't notice issues with that, but I'm
> sure there are cases I didn't cover. Did you discover any useful cases
> that broke after this patch or did you just notice it in code?

This behavior change was caught in our regression tests.