Re: [PATCH 1/2] mac80211: fix overflow issues in airtime fairness code

["Toke Høiland-Jørgensen" <toke@kernel.org>]

Felix Fietkau <nbd@nbd.name> writes:

> The airtime weight calculation overflows with a default weight value of 256
> whenever more than 8ms worth of airtime is reported.
> Bigger weight values impose even smaller limits on maximum airtime values.
> This can mess up airtime based calculations for drivers that don't report
> per-PPDU airtime values, but batch up values instead.
>
> Fix this by reordering multiplications/shifts and by reducing unnecessary
> intermediate precision (which was lost in a later stage anyway).
>
> The new shift value limits the maximum weight to 4096, which should be more
> than enough. Any values bigger than that will be clamped to the upper limit.
>
> Signed-off-by: Felix Fietkau <nbd@nbd.name>

The weights are UAPI, so I guess we could run into applications that
expect to be able to set a weight higher than 4096? I don't think this
is too likely, but maybe it is better to reject such attempts instead of
silently clamping the value, to flush out any breakage if it does occur?

-Toke