net80211: fix TKIP trailer trimming w/ no rx parameters given

[adrian]

Summary

Previous work made trimming the TKIP trailer an optional thing
based on what the driver indicated it did with the received
frame. However, for drivers that aren't populating an RX frame
with an rx status - notably iwn(4) - exposed this bug.

If the driver doesn't expose any RX status then just restore
the previous behaviour.

This should be considered a temporary (ish) workaround until we've
figured out a longer term approach to checking RX status information
from drivers and what the default (if any) behaviour should be.

Locally tested:

• iwn(4), STA mode, CCMP + TKIP groupwise network

[bz]

Need to check all the other places which may have changed implicit behaviour too and they all need the same comment,

sys/net80211/ieee80211_crypto_tkip.c

375

What about?

/* Code implicit legacy behavior until all drivers are converted. */
if (rxs == NULL || (rxs->c_pktflags & IEEE80211_RX_F_ICV_STRIP) == 0) ?

[adrian]

update from bz; matches what's in CCMP

[adrian]

In D50638#1156017, @bz wrote:

Need to check all the other places which may have changed implicit behaviour too and they all need the same comment,

it looks like ccmp and gcmp are OK. CCMP actually has the suggested fix from you here. :-)

[bz]

Important:

Please add:

Fixes:     731ff40069d28
MFC after: 3 days

I can do the MFC and handle the possible errata notice if you want me to given it's my bug; added re@ to this review.

Thankfully it seems all the other changes were indeed new or not changing the status quo. Cannot find any others matching
git diff 1eb3f15c149b.. sys/net80211 | grep 'rxs != NULL' | grep ==

[adrian]

update commit message (locally)