[PATCH 5.4 36/49] p54: avoid accessing the data mapped to streaming DMA

[Greg Kroah-Hartman]

From: Jia-Ju Bai <baijiaju@xxxxxxxxxxxxxxx>

commit 478762855b5ae9f68fa6ead1edf7abada70fcd5f upstream.

In p54p_tx(), skb->data is mapped to streaming DMA on line 337:
  mapping = pci_map_single(..., skb->data, ...);

Then skb->data is accessed on line 349:
  desc->device_addr = ((struct p54_hdr *)skb->data)->req_id;

This access may cause data inconsistency between CPU cache and hardware.

To fix this problem, ((struct p54_hdr *)skb->data)->req_id is stored in
a local variable before DMA mapping, and then the driver accesses this
local variable instead of skb->data.

Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Jia-Ju Bai <baijiaju@xxxxxxxxxxxxxxx>
Acked-by: Christian Lamparter <chunkeey@xxxxxxxxx>
Signed-off-by: Kalle Valo <kvalo@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200802132949.26788-1-baijiaju@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/wireless/intersil/p54/p54pci.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/net/wireless/intersil/p54/p54pci.c
+++ b/drivers/net/wireless/intersil/p54/p54pci.c
@@ -329,10 +329,12 @@ static void p54p_tx(struct ieee80211_hw
 	struct p54p_desc *desc;
 	dma_addr_t mapping;
 	u32 idx, i;
+	__le32 device_addr;
 
 	spin_lock_irqsave(&priv->lock, flags);
 	idx = le32_to_cpu(ring_control->host_idx[1]);
 	i = idx % ARRAY_SIZE(ring_control->tx_data);
+	device_addr = ((struct p54_hdr *)skb->data)->req_id;
 
 	mapping = pci_map_single(priv->pdev, skb->data, skb->len,
 				 PCI_DMA_TODEVICE);
@@ -346,7 +348,7 @@ static void p54p_tx(struct ieee80211_hw
 
 	desc = &ring_control->tx_data[i];
 	desc->host_addr = cpu_to_le32(mapping);
-	desc->device_addr = ((struct p54_hdr *)skb->data)->req_id;
+	desc->device_addr = device_addr;
 	desc->len = cpu_to_le16(skb->len);
 	desc->flags = 0;