rtlwifi: rtl8188ee: avoid accessing the data mapped to streaming DMA

In rtl88ee_tx_fill_cmddesc(), skb->data is mapped to streaming DMA on
line 677:
  dma_addr_t mapping = dma_map_single(..., skb->data, ...);

On line 680, 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 681:
  __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@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201119015127.12033-1-baijiaju1990@gmail.com

diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c b/drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c
index b9775ee..c948daf 100644 (file)
--- a/drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c
+++ b/drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c
@@ -674,12 +674,12 @@ void rtl88ee_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");