rtl8180: avoid accessing the data mapped to streaming DMA

In rtl8180_tx(), skb->data is mapped to streaming DMA on line 476:
  mapping = dma_map_single(..., skb->data, ...);

On line 459, skb->data is assigned to hdr after cast:
  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;

Then hdr->seq_ctrl is accessed on lines 540 and 541:
  hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
  hdr->seq_ctrl |= cpu_to_le16(priv->seqno);

These DMA accesses may cause data inconsistency between CPU and hardwre.

To fix this problem, hdr->seq_ctrl is accessed before the DMA mapping.

Signed-off-by: Jia-Ju Bai <redacted>
---
 drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c b/drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c
index 2477e18c7cae..cc73014aa5f3 100644
--- a/drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c
+++ b/drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c

@@ -473,6 +473,13 @@ static void rtl8180_tx(struct ieee80211_hw *dev,
 	prio = skb_get_queue_mapping(skb);
 	ring = &priv->tx_ring[prio];
 
+	if (info->flags & IEEE80211_TX_CTL_ASSIGN_SEQ) {
+		if (info->flags & IEEE80211_TX_CTL_FIRST_FRAGMENT)
+			priv->seqno += 0x10;
+		hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
+		hdr->seq_ctrl |= cpu_to_le16(priv->seqno);
+	}
+
 	mapping = dma_map_single(&priv->pdev->dev, skb->data, skb->len,
 				 DMA_TO_DEVICE);
 

@@ -534,13 +541,6 @@ static void rtl8180_tx(struct ieee80211_hw *dev,
 
 	spin_lock_irqsave(&priv->lock, flags);
 
-	if (info->flags & IEEE80211_TX_CTL_ASSIGN_SEQ) {
-		if (info->flags & IEEE80211_TX_CTL_FIRST_FRAGMENT)
-			priv->seqno += 0x10;
-		hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
-		hdr->seq_ctrl |= cpu_to_le16(priv->seqno);
-	}
-
 	idx = (ring->idx + skb_queue_len(&ring->queue)) % ring->entries;
 	entry = &ring->desc[idx];
 

-- 
2.17.1

On Mon, 19 Oct 2020 10:54:20 +0800 Jia-Ju Bai wrote:

You're taking the priv->seqno access and modification from under
priv->lock. Is that okay?

On 19.10.2020 04:54, Jia-Ju Bai wrote:

In rtl8180_tx(), skb->data is mapped to streaming DMA on line 476:
  mapping = dma_map_single(..., skb->data, ...);

On line 459, skb->data is assigned to hdr after cast:
  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;

Then hdr->seq_ctrl is accessed on lines 540 and 541:
  hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
  hdr->seq_ctrl |= cpu_to_le16(priv->seqno);

These DMA accesses may cause data inconsistency between CPU and hardwre.

To fix this problem, hdr->seq_ctrl is accessed before the DMA mapping.

This looks like a bug fix to me, shouldn't this have a Fixes: tag and
be CC'ed to stable@?

Maciej