[PATCH 1/2] rtl818x: Fix potential data race in rtl8187_tx_cb()

[Daniil Dulov <d.dulov@aladdin.ru>]

There is a potential data race between rtl8187_tx_cb() and rtl8187_stop().
It is possible for rtl8187_stop() to clear the queue right after rtl8187_tx_cb()
checks that queue has more than 5 elements, but before it dequeues any skb.
This results in skb_dequeue() returns NULL and the pointer is dereferenced
in ieee80211_tx_status_irqsafe().

 BUG: kernel NULL pointer dereference, address: 0000000000000080
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: Oops: 0000 [#1] SMP NOPTI
 CPU: 7 UID: 0 PID: 0 Comm: swapper/7 Not tainted 6.15.0 #8 PREEMPT(voluntary)
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
 RIP: 0010:ieee80211_tx_status_irqsafe+0x21/0xc0 [mac80211]
 Call Trace:
  <IRQ>
  rtl8187_tx_cb+0x116/0x150 [rtl8187]
  __usb_hcd_giveback_urb+0x9d/0x120
  usb_giveback_urb_bh+0xbb/0x140
  process_one_work+0x19b/0x3c0
  bh_worker+0x1a7/0x210
  tasklet_action+0x10/0x30
  handle_softirqs+0xf0/0x340
  __irq_exit_rcu+0xcd/0xf0
  common_interrupt+0x85/0xa0
  </IRQ>

In order to avoid potential data races and leading dereference of a NULL
pointer, acquire the queue lock before any work with the queue is done and
replace all skb_* calls with their lockless versions.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 3517afdefc3a ("rtl8187: feedback transmitted packets using tx close descriptor for 8187B")
Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
---
 .../net/wireless/realtek/rtl818x/rtl8187/dev.c    | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c b/drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c
index 220ac5bdf279..8fe6fdc32e56 100644
--- a/drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c
+++ b/drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c
@@ -189,6 +189,7 @@ static void rtl8187_tx_cb(struct urb *urb)
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 	struct ieee80211_hw *hw = info->rate_driver_data[0];
 	struct rtl8187_priv *priv = hw->priv;
+	unsigned long flags;
 
 	skb_pull(skb, priv->is_rtl8187b ? sizeof(struct rtl8187b_tx_hdr) :
 					  sizeof(struct rtl8187_tx_hdr));
@@ -196,7 +197,8 @@ static void rtl8187_tx_cb(struct urb *urb)
 
 	if (!(urb->status) && !(info->flags & IEEE80211_TX_CTL_NO_ACK)) {
 		if (priv->is_rtl8187b) {
-			skb_queue_tail(&priv->b_tx_status.queue, skb);
+			spin_lock_irqsave(&priv->b_tx_status.queue.lock, flags);
+			__skb_queue_tail(&priv->b_tx_status.queue, skb);
 
 			/* queue is "full", discard last items */
 			while (skb_queue_len(&priv->b_tx_status.queue) > 5) {
@@ -205,9 +207,11 @@ static void rtl8187_tx_cb(struct urb *urb)
 				dev_dbg(&priv->udev->dev,
 					"transmit status queue full\n");
 
-				old_skb = skb_dequeue(&priv->b_tx_status.queue);
+				old_skb = __skb_dequeue(&priv->b_tx_status.queue);
 				ieee80211_tx_status_irqsafe(hw, old_skb);
 			}
+
+			spin_unlock_irqrestore(&priv->b_tx_status.queue.lock, flags);
 			return;
 		} else {
 			info->flags |= IEEE80211_TX_STAT_ACK;
@@ -893,6 +897,7 @@ static void rtl8187_work(struct work_struct *work)
 				    work.work);
 	struct ieee80211_tx_info *info;
 	struct ieee80211_hw *dev = priv->dev;
+	unsigned long flags;
 	static u16 retry;
 	u16 tmp;
 	u16 avg_retry;
@@ -900,6 +905,8 @@ static void rtl8187_work(struct work_struct *work)
 
 	mutex_lock(&priv->conf_mutex);
 	tmp = rtl818x_ioread16(priv, (__le16 *)0xFFFA);
+
+	spin_lock_irqsave(&priv->b_tx_status.queue.lock, flags);
 	length = skb_queue_len(&priv->b_tx_status.queue);
 	if (unlikely(!length))
 		length = 1;
@@ -909,13 +916,15 @@ static void rtl8187_work(struct work_struct *work)
 	while (skb_queue_len(&priv->b_tx_status.queue) > 0) {
 		struct sk_buff *old_skb;
 
-		old_skb = skb_dequeue(&priv->b_tx_status.queue);
+		old_skb = __skb_dequeue(&priv->b_tx_status.queue);
 		info = IEEE80211_SKB_CB(old_skb);
 		info->status.rates[0].count = avg_retry + 1;
 		if (info->status.rates[0].count > RETRY_COUNT)
 			info->flags &= ~IEEE80211_TX_STAT_ACK;
 		ieee80211_tx_status_irqsafe(dev, old_skb);
 	}
+	spin_unlock_irqrestore(&priv->b_tx_status.queue.lock, flags);
+
 	retry = tmp;
 	mutex_unlock(&priv->conf_mutex);
 }
-- 
2.34.1