2020-10-19 10:02:36

by Jia-Ju Bai

Subject: [PATCH] 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 <[email protected]>
---
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

2020-10-19 18:46:16

by Jakub Kicinski

Subject: Re: [PATCH] rtl8180: avoid accessing the data mapped to streaming DMA

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

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