[PATCH v2 4/4 resend] rtlwifi: rtl8723ae: avoid accessing the data mapped to streaming DMA

[Jia-Ju Bai]

In rtl8723e_tx_fill_cmddesc(), skb->data is mapped to streaming DMA on
line 531:
  dma_addr_t mapping = dma_map_single(..., skb->data, ...);

On line 534, skb->data is assigned to hdr after cast:
  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)(skb->data);

Then hdr->frame_control is accessed on line 535:
  __le16 fc = hdr->frame_control;

This DMA access may cause data inconsistency between CPU and hardwre.

To fix this bug, hdr->frame_control is accessed before the DMA mapping.

Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
v2:
* Use "rtlwifi" as subject prefix and have all rtlwifi patches in the
  same pathset.
  Thank Ping and Larry for good advice.

---
 drivers/net/wireless/realtek/rtlwifi/rtl8723ae/trx.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8723ae/trx.c b/drivers/net/wireless/realtek/rtlwifi/rtl8723ae/trx.c
index e3ee91b7ea8d..340b3d68a54e 100644
--- a/drivers/net/wireless/realtek/rtlwifi/rtl8723ae/trx.c
+++ b/drivers/net/wireless/realtek/rtlwifi/rtl8723ae/trx.c
@@ -528,12 +528,12 @@ void rtl8723e_tx_fill_cmddesc(struct ieee80211_hw *hw,
 	u8 fw_queue = QSLT_BEACON;
 	__le32 *pdesc = (__le32 *)pdesc8;
 
-	dma_addr_t mapping = dma_map_single(&rtlpci->pdev->dev, skb->data,
-					    skb->len, DMA_TO_DEVICE);
-
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)(skb->data);
 	__le16 fc = hdr->frame_control;
 
+	dma_addr_t mapping = dma_map_single(&rtlpci->pdev->dev, skb->data,
+					    skb->len, DMA_TO_DEVICE);
+
 	if (dma_mapping_error(&rtlpci->pdev->dev, mapping)) {
 		rtl_dbg(rtlpriv, COMP_SEND, DBG_TRACE,
 			"DMA mapping error\n");
-- 
2.17.1