Re: [PATCH 2/2] eap-tls: Add session caching

[Denis Kenzior <denkenz@gmail.com>]

Hi Andrew,

<snip>

>> So if we index by
>>          a) SSID -> there's a good chance that we can reuse the session across routers,
>> even if that fails in some cases
>>          b) SSID + BSS -> We never try the session ID unless we have been connected to
>> the same BSS before.  In which case there's no advantage over PMK caching?
> 
> The flipside of this is:
>     a) SSID -> since we only store one session so everytime we switch
> BSSes we overwrite the cached session in the co-located AA case and
> rarely see the benefit of the cache.
>     b) BSSID -> we store one session for each BSS and after some number
> of reconnects every next one is going to be fast.
> 

So for case b, I would argue PMK caching would be even better since we skip 
8021x completely.  As I mentioned earlier, I would think that RADIUS server is 
the 'general' case and we should optimize for that.  Maybe I'm wrong here, but 
I've never seen a colocated option in any commercial APs.  It is always a RADIUS 
server.

> That said the RFC-recommended session lifetime being only 24h makes
> this less practical.  Since we can't know how long each server's
> session lifetime is I wonder if IWD should set it to a higher value in
> case we're lucky.

I'd just default to what the RFC recommends, but maybe we can add something to 
the profile to make this configurable.

<snip>

>> I would think we need to explicitly drop anything related to the SSID of the
>> network we just removed via KnownNetworks.Forget()
> 
> Ok.  I don't believe we do this for known frequencies though.
> 

I think we do?  See known_networks_remove()

<snip>

>>
>> Yes, but how does eap remove the relevant entries from the cache?
> 
> If we want to do this I'll probably move the cache singleton to
> knownnetworks.c and drop the relevant group and not notify eap.
> eap-tls-common.c would use something like
> known_networks_get_tls_session_cache().

That might be the way to go then.

Regards,
-Denis