wcn36xx: don't keep reference to skb if transmission failed

When wcn36xx_dxe_tx_frame() fails to transmit the TX frame, the driver
will call into ieee80211_free_txskb() for the skb in flight, so it'll no
longer be valid. Hence, we shouldn't keep a reference to it in ctl->skb.
Also, if the skb has IEEE80211_TX_CTL_REQ_TX_STATUS set, a pointer to
it will currently remain in wcn->tx_ack_skb, which will potentially lead
to a crash if accessed later.

Fix this by checking the return value of wcn36xx_dxe_tx_frame(), and
nullify wcn->tx_ack_skb again in case of errors. Move the assignment
of ctl->skb in wcn36xx_dxe_tx_frame() so it only happens when the
transmission is successful.
Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/wcn36xx/dxe.c

@@ -693,7 +693,6 @@ int wcn36xx_dxe_tx_frame(struct wcn36xx *wcn,
 
 	/* Set source address of the SKB we send */
 	ctl = ctl->next;
-	ctl->skb = skb;
 	desc = ctl->desc;
 	if (ctl->bd_cpu_addr) {
 		wcn36xx_err("bd_cpu_addr cannot be NULL for skb DXE\n");
@@ -702,8 +701,8 @@ int wcn36xx_dxe_tx_frame(struct wcn36xx *wcn,
 	}
 
 	desc->src_addr_l = dma_map_single(wcn->dev,
-					  ctl->skb->data,
-					  ctl->skb->len,
+					  skb->data,
+					  skb->len,
 					  DMA_TO_DEVICE);
 	if (dma_mapping_error(wcn->dev, desc->src_addr_l)) {
 		dev_err(wcn->dev, "unable to DMA map src_addr_l\n");
@@ -711,6 +710,7 @@ int wcn36xx_dxe_tx_frame(struct wcn36xx *wcn,
 		goto unlock;
 	}
 
+	ctl->skb = skb;
 	desc->dst_addr_l = ch->dxe_wq;
 	desc->fr_len = ctl->skb->len;
 

drivers/net/wireless/ath/wcn36xx/txrx.c

@@ -273,6 +273,7 @@ int wcn36xx_start_tx(struct wcn36xx *wcn,
 	bool bcast = is_broadcast_ether_addr(hdr->addr1) ||
 		is_multicast_ether_addr(hdr->addr1);
 	struct wcn36xx_tx_bd bd;
+	int ret;
 
 	memset(&bd, 0, sizeof(bd));
 
@@ -317,5 +318,17 @@ int wcn36xx_start_tx(struct wcn36xx *wcn,
 	buff_to_be((u32 *)&bd, sizeof(bd)/sizeof(u32));
 	bd.tx_bd_sign = 0xbdbdbdbd;
 
-	return wcn36xx_dxe_tx_frame(wcn, vif_priv, &bd, skb, is_low);
+	ret = wcn36xx_dxe_tx_frame(wcn, vif_priv, &bd, skb, is_low);
+	if (ret && bd.tx_comp) {
+		/* If the skb has not been transmitted,
+		 * don't keep a reference to it.
+		 */
+		spin_lock_irqsave(&wcn->dxe_lock, flags);
+		wcn->tx_ack_skb = NULL;
+		spin_unlock_irqrestore(&wcn->dxe_lock, flags);
+
+		ieee80211_wake_queues(wcn->hw);
+	}
+
+	return ret;
 }