[PATCH net v2] net: lantiq: fix memory corruption in RX ring

[Aleksander Jan Bajkowski <olek2@wp.pl>]

In a situation where memory allocation or dma mapping fails, an
invalid address is programmed into the descriptor. This can lead
to memory corruption. If the memory allocation fails, DMA should
reuse the previous skb and mapping and drop the packet. This patch
also increments rx drop counter.

Fixes: fe1a56420cf2 ("net: lantiq: Add Lantiq / Intel VRX200 Ethernet driver ")
Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
---
 drivers/net/ethernet/lantiq_xrx200.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/lantiq_xrx200.c b/drivers/net/ethernet/lantiq_xrx200.c
index 41c2ad210bc9..36dc3e5f6218 100644
--- a/drivers/net/ethernet/lantiq_xrx200.c
+++ b/drivers/net/ethernet/lantiq_xrx200.c
@@ -154,6 +154,7 @@ static int xrx200_close(struct net_device *net_dev)
 
 static int xrx200_alloc_skb(struct xrx200_chan *ch)
 {
+	dma_addr_t mapping;
 	int ret = 0;
 
 	ch->skb[ch->dma.desc] = netdev_alloc_skb_ip_align(ch->priv->net_dev,
@@ -163,16 +164,17 @@ static int xrx200_alloc_skb(struct xrx200_chan *ch)
 		goto skip;
 	}
 
-	ch->dma.desc_base[ch->dma.desc].addr = dma_map_single(ch->priv->dev,
-			ch->skb[ch->dma.desc]->data, XRX200_DMA_DATA_LEN,
-			DMA_FROM_DEVICE);
-	if (unlikely(dma_mapping_error(ch->priv->dev,
-				       ch->dma.desc_base[ch->dma.desc].addr))) {
+	mapping = dma_map_single(ch->priv->dev, ch->skb[ch->dma.desc]->data,
+				 XRX200_DMA_DATA_LEN, DMA_FROM_DEVICE);
+	if (unlikely(dma_mapping_error(ch->priv->dev, mapping))) {
 		dev_kfree_skb_any(ch->skb[ch->dma.desc]);
 		ret = -ENOMEM;
 		goto skip;
 	}
 
+	ch->dma.desc_base[ch->dma.desc].addr = mapping;
+	/* Make sure the address is written before we give it to HW */
+	wmb();
 skip:
 	ch->dma.desc_base[ch->dma.desc].ctl =
 		LTQ_DMA_OWN | LTQ_DMA_RX_OFFSET(NET_IP_ALIGN) |
@@ -196,6 +198,8 @@ static int xrx200_hw_receive(struct xrx200_chan *ch)
 	ch->dma.desc %= LTQ_DESC_NUM;
 
 	if (ret) {
+		ch->skb[ch->dma.desc] = skb;
+		net_dev->stats.rx_dropped++;
 		netdev_err(net_dev, "failed to allocate new rx buffer\n");
 		return ret;
 	}
-- 
2.30.2