Re: [PATCH] mac80211: Use sw crypto for GTKs on AP VLAN interfaces

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2010-11-18 at 16:36 +0100, Helmut Schaa wrote:
> When using AP VLAN interfaces, each VLAN interface should be in its own
> broadcast domain. Hostapd achieves this by assigning different GTKs to
> different AP VLAN interfaces.
> 
> However, mac80211 drivers are not aware of AP VLAN interfaces and as
> such mac80211 sends the GTK to the driver in the context of the base AP
> mode interface. This causes problems when multiple AP VLAN interfaces
> are used since the driver will use the same key slot for the different
> GTKs (there's no way for the driver to distinguish the different GTKs
> from different AP VLAN interfaces). Thus, only the clients associated
> to one AP VLAN interface (the one that was created last) can actually
> use broadcast traffic.
> 
> Fix this by not programming any GTKs for AP VLAN interfaces into the hw
> but fall back to using software crypto. The GTK for the underlying AP
> interface is still sent to the driver.
> 
> That means, broadcast traffic to and from stations associated to an AP
> VLAN interface is encrypted and decrypted in software whereas broadcast
> traffic to and from stations associated to the non-VLAN AP interface is
> encrypted end decrypted in hardware.

Minor nit: bcast traffic from stations is never decrypted by these keys
since stations never send real bcast frames -- just remove the decyrpted
part and "from stations" part :-)

> Cc: Johannes Berg <johannes@sipsolutions.net>
> Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
> ---
> 
> This incidentally also fixes the mac8011 oops related to AP VLAN
> interfaces I've reported earlier.
> 
> If we want to support hardware crypto for broadcast traffic on AP VLAN
> interfaces we'd either need to switch to per station GTKs or need to
> make drivers aware of VLAN interfaces. Not sure if it's worth it.
> 
> At least current rt2x00 devices won't be able to support that due to
> the limited amount of available key space.


Hmm, good point. Jouni, any comments? Lennert maybe?

johannes

>  net/mac80211/key.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/net/mac80211/key.c b/net/mac80211/key.c
> index ccd676b..72df1ca 100644
> --- a/net/mac80211/key.c
> +++ b/net/mac80211/key.c
> @@ -84,10 +84,17 @@ static int ieee80211_key_enable_hw_accel(struct ieee80211_key *key)
>  		goto out_unsupported;
>  
>  	sdata = key->sdata;
> -	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
> +	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN) {
> +		/*
> +		 * The driver doesn't know anything about VLAN interfaces.
> +		 * Hence, don't send GTKs for VLAN interfaces to the driver.
> +		 */
> +		if (!(key->conf.flags & IEEE80211_KEY_FLAG_PAIRWISE))
> +			goto out_unsupported;
>  		sdata = container_of(sdata->bss,
>  				     struct ieee80211_sub_if_data,
>  				     u.ap);
> +	}
>  
>  	ret = drv_set_key(key->local, SET_KEY, sdata, sta, &key->conf);
>