net: mvneta: fix refilling for Rx DMA buffers

With the actual code, if a memory allocation error happens while
refilling a Rx descriptor, then the original Rx buffer is both passed
to the networking stack (in a SKB) and let in the Rx ring. This leads
to various kernel oops and crashes.

As a fix, this patch moves Rx descriptor refilling ahead of building
SKB with the associated Rx buffer. In case of a memory allocation
failure, data is dropped and the original DMA buffer is put back into
the Rx ring.

Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
Fixes: c5aff18204da ("net: mvneta: driver for Marvell Armada 370/XP network unit")
Cc: <stable@vger.kernel.org> # v3.8+
Tested-by: Yoann Sculo <yoann@sculo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -1462,7 +1462,7 @@ static int mvneta_rx(struct mvneta_port *pp, int rx_todo,
 		     struct mvneta_rx_queue *rxq)
 {
 	struct net_device *dev = pp->dev;
-	int rx_done, rx_filled;
+	int rx_done;
 	u32 rcvd_pkts = 0;
 	u32 rcvd_bytes = 0;
 
@@ -1473,7 +1473,6 @@ static int mvneta_rx(struct mvneta_port *pp, int rx_todo,
 		rx_todo = rx_done;
 
 	rx_done = 0;
-	rx_filled = 0;
 
 	/* Fairness NAPI loop */
 	while (rx_done < rx_todo) {
@@ -1484,7 +1483,6 @@ static int mvneta_rx(struct mvneta_port *pp, int rx_todo,
 		int rx_bytes, err;
 
 		rx_done++;
-		rx_filled++;
 		rx_status = rx_desc->status;
 		rx_bytes = rx_desc->data_size - (ETH_FCS_LEN + MVNETA_MH_SIZE);
 		data = (unsigned char *)rx_desc->buf_cookie;
@@ -1524,6 +1522,14 @@ static int mvneta_rx(struct mvneta_port *pp, int rx_todo,
 			continue;
 		}
 
+		/* Refill processing */
+		err = mvneta_rx_refill(pp, rx_desc);
+		if (err) {
+			netdev_err(dev, "Linux processing - Can't refill\n");
+			rxq->missed++;
+			goto err_drop_frame;
+		}
+
 		skb = build_skb(data, pp->frag_size > PAGE_SIZE ? 0 : pp->frag_size);
 		if (!skb)
 			goto err_drop_frame;
@@ -1543,14 +1549,6 @@ static int mvneta_rx(struct mvneta_port *pp, int rx_todo,
 		mvneta_rx_csum(pp, rx_status, skb);
 
 		napi_gro_receive(&pp->napi, skb);
-
-		/* Refill processing */
-		err = mvneta_rx_refill(pp, rx_desc);
-		if (err) {
-			netdev_err(dev, "Linux processing - Can't refill\n");
-			rxq->missed++;
-			rx_filled--;
-		}
 	}
 
 	if (rcvd_pkts) {
@@ -1563,7 +1561,7 @@ static int mvneta_rx(struct mvneta_port *pp, int rx_todo,
 	}
 
 	/* Update rxq management counters */
-	mvneta_rxq_desc_num_update(pp, rxq, rx_done, rx_filled);
+	mvneta_rxq_desc_num_update(pp, rxq, rx_done, rx_done);
 
 	return rx_done;
 }