Re: [PATCH] mac80211: fix AP_VLAN crypto tailroom calculation

[Johannes Berg <johannes@sipsolutions.net>]

On Mon, 2015-05-11 at 13:05 +0000, Michal Kazior wrote:
> AP_VLANs may inherit crypto keys from parent AP.
> Moreover AP_VLANs may have PTK keys of their own.
> Hence both AP_VLAN sdata and AP sdata must be
> inspected.
> 
> Some splats I was seeing:
> 
>  (a) WARNING: CPU: 1 PID: 0 at /devel/src/linux/net/mac80211/wep.c:102 ieee80211_wep_add_iv
>  (b) WARNING: CPU: 1 PID: 0 at /devel/src/linux/net/mac80211/wpa.c:73 ieee80211_tx_h_michael_mic_add
>  (c) WARNING: CPU: 3 PID: 0 at /devel/src/linux/net/mac80211/wpa.c:433 ieee80211_crypto_ccmp_encrypt
> 
> I've seen (a) and (b) with ath9k hw crypto and (c)
> with ath9k sw crypto. All of them were related to
> insufficient skb tailroom and I was able to
> trigger these with ping6 program.
> 
> This patch effectively fixes Tx when using
> AP_VLANs with WEP and WPA in some setups.
> 
> Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
> ---
>  net/mac80211/tx.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index 8df134213adf..0887d6e5c424 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -1593,6 +1593,25 @@ static bool ieee80211_tx(struct ieee80211_sub_if_data *sdata,
>  
>  /* device xmit handlers */
>  
> +static bool
> +ieee80211_need_crypto_tx_tailroom(struct ieee80211_sub_if_data *sdata)
> +{
> +	struct ieee80211_sub_if_data *parent_sdata;
> +
> +	if (sdata->crypto_tx_tailroom_needed_cnt)
> +		return true;
> +
> +	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN && sdata->bss) {
> +		parent_sdata = container_of(sdata->bss,
> +					    struct ieee80211_sub_if_data,
> +					    u.ap);
> +		if (parent_sdata->crypto_tx_tailroom_needed_cnt)
> +			return true;
> +	}
> +
> +	return false;
> +}
> +
>  static int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
>  				struct sk_buff *skb,
>  				int head_need, bool may_encrypt)
> @@ -1600,7 +1619,7 @@ static int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
>  	struct ieee80211_local *local = sdata->local;
>  	int tail_need = 0;
>  
> -	if (may_encrypt && sdata->crypto_tx_tailroom_needed_cnt) {
> +	if (may_encrypt && ieee80211_need_crypto_tx_tailroom(sdata)) {

This makes that check far more inefficient - I think you should write it
differently and have the management code copy the value to the VLAN
interfaces so the existing check here is sufficient.

johannes