Re: [PATCH] usb: gadget: u_ether: fix race in setting MAC address in setup phase

[Greg Kroah-Hartman]

On Tue, Nov 30, 2021 at 12:12:29AM +0200, Marian Postevca wrote:
> When listening for notifications through netlink of a new interface being
> registered, sporadically, it is possible for the MAC to be read as zero.
> The zero MAC address lasts a short period of time and then switches to a
> valid random MAC address.
> 
> This causes problems for netd in Android, which assumes that the interface
> is malfunctioning and will not use it.
> 
> In the good case we get this log:
> InterfaceController::getCfg() ifName usb0
>  hwAddr 92:a8:f0:73:79:5b ipv4Addr 0.0.0.0 flags 0x1002
> 
> In the error case we get these logs:
> InterfaceController::getCfg() ifName usb0
>  hwAddr 00:00:00:00:00:00 ipv4Addr 0.0.0.0 flags 0x1002
> 
> netd : interfaceGetCfg("usb0")
> netd : interfaceSetCfg() -> ServiceSpecificException
>  (99, "[Cannot assign requested address] : ioctl() failed")
> 
> The reason for the issue is the order in which the interface is setup,
> it is first registered through register_netdev() and after the MAC
> address is set.
> 
> Fixed by first setting the MAC address of the net_device and after that
> calling register_netdev().
> 
> Signed-off-by: Marian Postevca <posteuca@xxxxxxxxx>
> ---
>  drivers/usb/gadget/function/u_ether.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)

What commit does this fix?  Should it go to stable kernel releases?

thanks,

greg k-h