mt76: dma: do not build skb if reported len does not fit in buf_size

Precompute data length in order to avoid to allocate the related
skb data structure if reported length does not fit in queue buf_size
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/dma.c

@@ -417,10 +417,9 @@ mt76_add_fragment(struct mt76_dev *dev, struct mt76_queue *q, void *data,
 static int
 mt76_dma_rx_process(struct mt76_dev *dev, struct mt76_queue *q, int budget)
 {
+	int len, data_len, done = 0;
 	struct sk_buff *skb;
 	unsigned char *data;
-	int len;
-	int done = 0;
 	bool more;
 
 	while (done < budget) {
@@ -430,7 +429,12 @@ mt76_dma_rx_process(struct mt76_dev *dev, struct mt76_queue *q, int budget)
 		if (!data)
 			break;
 
-		if (q->buf_size < len + q->buf_offset) {
+		if (q->rx_head)
+			data_len = q->buf_size;
+		else
+			data_len = SKB_WITH_OVERHEAD(q->buf_size);
+
+		if (data_len < len + q->buf_offset) {
 			dev_kfree_skb(q->rx_head);
 			q->rx_head = NULL;
 
@@ -448,12 +452,7 @@ mt76_dma_rx_process(struct mt76_dev *dev, struct mt76_queue *q, int budget)
 			skb_free_frag(data);
 			continue;
 		}
-
 		skb_reserve(skb, q->buf_offset);
-		if (skb->tail + len > skb->end) {
-			dev_kfree_skb(skb);
-			continue;
-		}
 
 		if (q == &dev->q_rx[MT_RXQ_MCU]) {
 			u32 *rxfce = (u32 *) skb->cb;