[PATCH] ap: never disconnect idle stations sooner than ap_max_inactivity

[Jouni Malinen]

On Sat, Sep 26, 2026 at 08:39:57AM -0700, hc86862997 at gmail.com wrote:
> hostapd adopts the client-advertised BSS Max Idle Period from the
> (re)association request and lets it override the AP-wide
> ap_max_inactivity, in two places:
> 
> - ap_handle_timer():
>     if (sta->max_idle_period)
>             max_inactivity = (sta->max_idle_period * 1024 + 999) / 1000;
> - ap_sta_alloc(): the same computation for the initial timer
>   registration.
> 
> Some clients (Apple) advertise a short BSS Max Idle Period (~20 units,
> about 20 s) for power saving - they expect the AP to buffer frames for
> them, not to be disconnected. The result is deterministic: with the
> screen off (idle), the client is removed exactly 20 s after
> association:

The BSS max idle period indicated in the (Re)Association Request frame
is an explicit request from the STA to use the provided idle timeout. If
it is known that the particular clients referenced here do this
incorrectly (i.e., ask for 20000 TUs but do not send keep-alive frames
before that times out), this should be reported to the STA vendor as an
issue that needs to be fixed in the STA.

> Raising ap_max_inactivity has no effect for such clients because the
> adoption overwrites it

By design.. I.e., that is the correct AP behavior on accepting a STA
requested value.

> Fix: never disconnect a station sooner than the AP-wide
> ap_max_inactivity - floor the adopted value in both places.

That would break the expected functionality. The correct fix for this
would be to fix the STA. If that is not doable, potentially adding a new
configuration parameter to add a minimum acceptable timeout from STA
could be considered as a workaround (i.e., min_acceptable_idle_period to
complement the already available max_acceptable_idle_period).

> Verification: an Apple MLO client left idle with the screen off was
> previously kicked at exactly 20 s on every attempt; with this patch it
> stays associated indefinitely. Clients that do not advertise BSS Max
> Idle Period are unaffected. (Also reported to OpenWrt:
> https://github.com/openwrt/openwrt/issues/25416 )
> 
> ---

Please read the top level CONTRIBUTIONS file. I would need a
Signed-off-by: line from the author or copyright holder of the patch to
be able to consider applying it to hostap.git.

-- 
Jouni Malinen                                            PGP id EFC895FA