[PATCH v3 2/7] net: moxa: fix build_skb() memory corruption

From: Jonas Jensen
Date: Mon Jan 20 2014 - 06:16:25 EST

DMA buffer memory must be synchronized and copied before passing skb to
napi_gro_receive(). The use of build_skb() can lead to memory corruption,
replace it with netdev_alloc_skb_ip_align() and memcpy().

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=69041

Signed-off-by: Jonas Jensen <jonas.jensen@xxxxxxxxx>

This fixes the following error on wget download (or ncftp),
usually after only a few seconds:

"read error: Bad address"

On receiving this error, wget exits. The download is not resumed (busybox default).

Applies to next-20140120

drivers/net/ethernet/moxa/moxart_ether.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/moxa/moxart_ether.c b/drivers/net/ethernet/moxa/moxart_ether.c
index aa45607..17c9f0e 100644
--- a/drivers/net/ethernet/moxa/moxart_ether.c
+++ b/drivers/net/ethernet/moxa/moxart_ether.c
@@ -226,14 +226,21 @@ static int moxart_rx_poll(struct napi_struct *napi, int budget)
if (len > RX_BUF_SIZE)
len = RX_BUF_SIZE;

- skb = build_skb(priv->rx_buf[rx_head], priv->rx_buf_size);
+ dma_sync_single_for_cpu(&ndev->dev,
+ priv->rx_mapping[rx_head],
+ priv->rx_buf_size, DMA_FROM_DEVICE);
+ skb = netdev_alloc_skb_ip_align(ndev, len);
if (unlikely(!skb)) {
- net_dbg_ratelimited("build_skb failed\n");
+ net_dbg_ratelimited("netdev_alloc_skb_ip_align failed\n");
+ memcpy(skb->data, priv->rx_buf[rx_head], len);
skb_put(skb, len);
+ dma_sync_single_for_device(&ndev->dev,
+ priv->rx_mapping[rx_head],
+ priv->rx_buf_size, DMA_FROM_DEVICE);
skb->protocol = eth_type_trans(skb, ndev);
napi_gro_receive(&priv->napi, skb);

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