We actually cover (2) for some cases by "accident" since
ieee80211_rx_h_decrypt() assigns rx->key to rx->sta->gtk[i] if one is
available. I'm not completely sure this is correct since it applies
to management frame as well, but that's the way commit
897bed8b4320774e56f282cdc1cceb4d77442797 ('mac80211: clean up RX key
checks') implemented it (Johannes: Could you please take a look
whether that gtk[] case was really supposed to apply for non-Data
frames?).

Hm, yeah, that's kinda questionable.

AFAICT we still do the right thing since ieee80211_drop_unencrypted()
contains a check for ieee80211_is_data() and we return in this if
branch, so we never get to the TAINTED check or the actual decrypt.

We could try to just drop unencrypted data frames (that aren't control
port protocol) right here, but it might wreak havoc with the reorder
buffer in case it (erroneously) happens.

johannes