Re: [RFC PATCH v2 2/2] mac80211: Add support for Extended Key ID

[Alexander Wetzel <alexander@wetzel-home.de>]

>> + * @IEEE80211_KEY_FLAG_RX_ONLY: Set by mac80211 to indicate that the key
>> + *      must not be used for TX (yet).
> 
> I'm not sure that's relevant, since you have one key pointer for TX?
> 
>> + * @IEEE80211_KEY_FLAG_SET_TX: Set by mac80211 to indicate that a previously
>> + *      installed key with IEEE80211_KEY_FLAG_RX_ONLY should take over TX also.
> 
> That also doesn't seem relevant ...
> 
> Oh, all of this is for HW offloads?
> 
> I _think_ I would prefer to have new key ops instead. Now you'd have
> 
> SET_KEY / <empty flags>
> SET_KEY / RX_ONLY
> SET_KEY / SET_TX
> 
> but I think maybe
> 
> SET_KEY
> SET_KEY_RX_ONLY
> KEY_ENABLE_TX
> 
> would make more sense?

Fine for me and should make it more understandable. So I'll try that.

> 
>> +	if (pairwise && params->flag == NL80211_KEY_SET_TX) {
>> +		mutex_lock(&local->sta_mtx);
>> +		sta = sta_info_get_bss(sdata, mac_addr);
>> +
>> +		if (!sta ||
>> +		   !(key = rcu_dereference(sta->ptk[key_idx])) ||
> 
> indentation here is off by one
> 
Thanks.

>> +		   !(key->conf.flags | IEEE80211_KEY_FLAG_RX_ONLY)) {
> 
> that makes no sense, should be & I guess
>
yes, I think that was one of the bugs I fixed the last weeks:-)


>> -	/* PTK only using key ID 0 needs special handling on rekey */
>> -	if (new_key && sta && ptk0rekey) {
>> +	/* PTK rekey without Extended Key ID needs special handling */
>> +	if (new_key && pairwise && sta &&
>> +	    !test_sta_flag(sta, WLAN_STA_EXT_KEY_ID)) {
>>   		local = old_key->local;
>>   		sdata = old_key->sdata;
> 
> This seems wrong, even if you have ext key ID support and everything,
> but you do 0 -> 0 rekeying, then you still need all the special handling
> (in fact also then if you go 1->1!). So it seems you'd instead want to
> see if you're going from a TX key to a TX key with the same key ID, and
> then you don't need this flag at all.
> 
The intention for Extended Key ID is, to have a comparable short time 
frame where both key IDs can be used. When replacing e.g. key ID 0 again 
it should be idle for a long time. I guess if someone starts re-keying 
in 1s intervals it may become an issue, but then anyone re-keying that 
often can't be helped...

With Extended Key IDs it's impossible to directly switch from a TX key 
with one key ID to another one with the same id.

1) Association
2) key ID 0 installed RX only
3) key Id 0 set_tx
4) rekey timeout passes
5) key ID 1 installed RX only
6) key ID 1 set_tx (also making key ID 0 RX only)
7) rekey timeout passes
8) key ID 0 replaced with new RX only key
9) key ID 0 set_tx
10) rekey timeout passes
...

So nobody will use the key being replaced, we don't have to protect 
against PN poisoning. And when a driver supports Extended Key ID we 
don't care about if the driver is able to rekey PTK0 correctly.


>> +++ b/net/mac80211/sta_info.c
>> @@ -350,6 +350,7 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
>>   	sta->sta.max_rx_aggregation_subframes =
>>   		local->hw.max_rx_aggregation_subframes;
>>   
>> +	sta->ptk_idx = NUM_DEFAULT_KEYS - 1;
> 
> That makes no sense? Why should it be 3? That's invalid anyway?

Yes, that's the whole reason for that change:-) Setting it to 2 would 
also be fine, as long as it's not 0 or 1.

ieee80211_tx_h_select_key starts encrypting packets as soon as 
sta->ptk[tx->sta->ptk_idx] is not null.

So installing the first key as RX only will also activate the key for 
TX. the AP will therefore encrypt EAPOL #3 of the initial connect...

To avoid expensive run time checks I simply switched the default setting 
to make sure sta->ptk[tx->sta->ptk_idx] will be NULL at the initial key 
install.

Alexander