Re: [PATCH] mac80211: prevent skb/txq mismatch

[Mohammed Shafi Shajakhan <mohammed@codeaurora.org>]

On Thu, Jan 12, 2017 at 03:28:41PM +0100, Michal Kazior wrote:
> Station structure is considered as not uploaded
> (to driver) until drv_sta_state() finishes. This
> call is however done after the structure is
> attached to mac80211 internal lists and hashes.
> This means mac80211 can lookup (and use) station
> structure before it is uploaded to a driver.
> 
> If this happens (structure exists, but
> sta->uploaded is false) fast_tx path can still be
> taken. Deep in the fastpath call the sta->uploaded
> is checked against to derive "pubsta" argument for
> ieee80211_get_txq(). If sta->uploaded is false
> (and sta is actually non-NULL) ieee80211_get_txq()
> effectively downgraded to vif->txq.
> 
> At first glance this may look innocent but coerces
> mac80211 into a state that is almost guaranteed
> (codel may drop offending skb) to crash because a
> station-oriented skb gets queued up on
> vif-oriented txq. The ieee80211_tx_dequeue() ends
> up looking at info->control.flags and tries to use
> txq->sta which in the fail case is NULL.
> 
> It's probably pointless to pretend one can
> downgrade skb from sta-txq to vif-txq.
> 
> Only drivers using wake_tx_queue were affected.
> 
> Example crash dump before fix:
> 
>  Unable to handle kernel paging request at virtual address ffffe26c
>  PC is at ieee80211_tx_dequeue+0x204/0x690 [mac80211]
>  [<bf4252a4>] (ieee80211_tx_dequeue [mac80211]) from
>  [<bf4b1388>] (ath10k_mac_tx_push_txq+0x54/0x1c0 [ath10k_core])
>  [<bf4b1388>] (ath10k_mac_tx_push_txq [ath10k_core]) from
>  [<bf4bdfbc>] (ath10k_htt_txrx_compl_task+0xd78/0x11d0 [ath10k_core])
>  [<bf4bdfbc>] (ath10k_htt_txrx_compl_task [ath10k_core])
>  [<bf51c5a4>] (ath10k_pci_napi_poll+0x54/0xe8 [ath10k_pci])
>  [<bf51c5a4>] (ath10k_pci_napi_poll [ath10k_pci]) from
>  [<c0572e90>] (net_rx_action+0xac/0x160)
> 
> Reported-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
> Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>

> ---
>  net/mac80211/tx.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index 4dea18be385c..c77fcf83d004 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -1244,13 +1244,16 @@ ieee80211_tx_prepare(struct ieee80211_sub_if_data *sdata,
>  
>  static struct txq_info *ieee80211_get_txq(struct ieee80211_local *local,
>  					  struct ieee80211_vif *vif,
> -					  struct ieee80211_sta *pubsta,
> +					  struct sta_info *sta,
>  					  struct sk_buff *skb)
>  {
>  	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
>  	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
>  	struct ieee80211_txq *txq = NULL;
>  
> +	if (sta && !sta->uploaded)
> +		return NULL;
> +
>  	if ((info->flags & IEEE80211_TX_CTL_SEND_AFTER_DTIM) ||
>  	    (info->control.flags & IEEE80211_TX_CTRL_PS_RESPONSE))
>  		return NULL;
> @@ -1258,10 +1261,10 @@ static struct txq_info *ieee80211_get_txq(struct ieee80211_local *local,
>  	if (!ieee80211_is_data(hdr->frame_control))
>  		return NULL;
>  
> -	if (pubsta) {
> +	if (sta) {
>  		u8 tid = skb->priority & IEEE80211_QOS_CTL_TID_MASK;
>  
> -		txq = pubsta->txq[tid];
> +		txq = sta->sta.txq[tid];
>  	} else if (vif) {
>  		txq = vif->txq;
>  	}
> @@ -1504,23 +1507,17 @@ static bool ieee80211_queue_skb(struct ieee80211_local *local,
>  	struct fq *fq = &local->fq;
>  	struct ieee80211_vif *vif;
>  	struct txq_info *txqi;
> -	struct ieee80211_sta *pubsta;
>  
>  	if (!local->ops->wake_tx_queue ||
>  	    sdata->vif.type == NL80211_IFTYPE_MONITOR)
>  		return false;
>  
> -	if (sta && sta->uploaded)
> -		pubsta = &sta->sta;
> -	else
> -		pubsta = NULL;
> -
>  	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
>  		sdata = container_of(sdata->bss,
>  				     struct ieee80211_sub_if_data, u.ap);
>  
>  	vif = &sdata->vif;
> -	txqi = ieee80211_get_txq(local, vif, pubsta, skb);
> +	txqi = ieee80211_get_txq(local, vif, sta, skb);
>  
>  	if (!txqi)
>  		return false;
> -- 
> 2.1.4
>