Re: [PATCH] net: usb: rtl8150: don't incorrectly assign random MAC addresses

[Jakub Kicinski]

On Sun, 11 Oct 2020 00:14:05 +0530 Anant Thazhemadam wrote:
> Ah, my apologies. You're right. It doesn't look like those helpers have made
> their way into the networking tree yet.
> 
> (This gets mentioned here as well,
>     https://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg357843.html)
> 
> The commit ID pointed to by the fixes tag is correct.
> The change introduced by said commit looks right, but is logically incorrect.
> 
> get_registers() directly returns the return value of usb_control_msg_recv(),
> and usb_control_msg_recv() returns 0 on success and negative error number
> otherwise.
> 
> (You can find more about the new helpers here
>     https://lore.kernel.org/alsa-devel/20200914153756.3412156-1-gregkh@xxxxxxxxxxxxxxxxxxx/ )
> 
> The commit ID mentioned introduces a change that is supposed to copy over
> the ethernet only when get_registers() succeeds, i.e., a complete read occurs,
> and generate and set a random ethernet address otherwise (reading the
> commit message should give some more insight).
> 
> The condition that checks if get_registers() succeeds (as specified in f45a4248ea4c)
> was,
>     ret == sizeof(node_id)
> where ret is the return value of get_registers().
> 
> However, ret will never equal sizeof(node_id), since ret can only be equal to 0
> or a negative number.
> 
> Thus, even in case where get_registers() succeeds, a randomly generated MAC
> address would get copied over, instead of copying the appropriate ethernet
> address, which is logically incorrect and not optimal.
> 
> Hence, we need to modify this to check if (ret == 0), and copy over the correct
> ethernet address in that case, instead of randomly generating one and assigning
> that.

I see... so we ended up with your fix applied to net, and Petko's
rework applied to the usb/usb-next tree.

What you're actually fixing is the improper resolution of the resulting
conflict in linux-next!

CCing Stephen and linux-next.