Re: [RFC 0/1] Allow MAC change on up interface

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2019-08-15 at 11:57 -0700, James Prestwood wrote:
> This is an example of how a devices MAC address could be changed while
> the interface is up. Currently RTNL and mac80211 both require the
> interface be down before changing the MAC.
> 
> After poking around a bit I found that some drivers can actually
> change the MAC while the iface is up. Allowing user space to do this
> while the iface is up would elminate a few potential race conditions
> that arise when changing the MAC from user space.
> 
> This commit does a few things:
>  - Adds an EXT_FEATURE that user space can check to see if the driver
>    allows this MAC changing.
>  - Adds a new NL80211_ATTR for including a "random mac" to     
>    CMD_CONNECT. This MAC is passed down the stack and gets set to 
>    the net_device's address.
>  - Set this wiphy extended feature in iwlwifi (just as an example)
>  - Relax checks in mac80211 which check if the interface is running
>  - Set IFF_LIVE_ADDR_CHANGE on net_device. Note: I know setting this
>    where I did is likely not the right way to do it, but for this
>    proof-of-concept it works. With guidance I can move this around
>    to a proper place.


It actually seems wrong to set IFF_LIVE_ADDR_CHANGE at all, because you
don't actually support that - you only support setting it while not
connected?

johannes