Re: [PATCH 1/1] wifi: ath9k: hif_usb: fix memory leak of remain_skbs

hif_dev->remain_skb is allocated and used exclusively in
ath9k_hif_usb_rx_stream(). It is implied that an allocated remain_skb is
processed and subsequently freed (in error paths) only during the next
call of ath9k_hif_usb_rx_stream().

So, if the device is deinitialized between those two calls or if the skb
contents are incorrect, it is possible that ath9k_hif_usb_rx_stream() is
not called next time and the allocated remain_skb is leaked. Our local
Syzkaller instance was able to trigger that.

Fix the leak by introducing a function to explicitly free remain_skb (if
it is not NULL) when the device is being deinitialized. remain_skb is NULL
when it has not been allocated at all (hif_dev struct is kzalloced) or
when it has been proccesed in next call to ath9k_hif_usb_rx_stream().

Proper spinlocks are held to prevent possible concurrent access to
remain_skb from the interrupt context ath9k_hif_usb_rx_stream(). These
accesses should not happen as rx_urbs have been deallocated before but
it prevents a dangerous race condition in these cases.

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

Fixes: fb9987d0f748 ("ath9k_htc: Support for AR9271 chipset.")
Signed-off-by: Fedor Pchelkin <redacted>
Signed-off-by: Alexey Khoroshilov <redacted>
---
 drivers/net/wireless/ath/ath9k/hif_usb.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/net/wireless/ath/ath9k/hif_usb.c b/drivers/net/wireless/ath/ath9k/hif_usb.c
index f521dfa2f194..e03ab972edf7 100644
--- a/drivers/net/wireless/ath/ath9k/hif_usb.c
+++ b/drivers/net/wireless/ath/ath9k/hif_usb.c

@@ -534,6 +534,23 @@ static struct ath9k_htc_hif hif_usb = {
 	.send = hif_usb_send,
 };
 
+/* Need to free remain_skb allocated in ath9k_hif_usb_rx_stream
+ * in case ath9k_hif_usb_rx_stream wasn't called next time to
+ * process the buffer and subsequently free it.
+ */
+static void ath9k_hif_usb_free_rx_remain_skb(struct hif_device_usb *hif_dev)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&hif_dev->rx_lock, flags);
+	if (hif_dev->remain_skb) {
+		dev_kfree_skb_any(hif_dev->remain_skb);
+		hif_dev->remain_skb = NULL;
+		hif_dev->rx_remain_len = 0;
+	}
+	spin_unlock_irqrestore(&hif_dev->rx_lock, flags);
+}
+
 static void ath9k_hif_usb_rx_stream(struct hif_device_usb *hif_dev,
 				    struct sk_buff *skb)
 {

@@ -1129,6 +1146,7 @@ static int ath9k_hif_usb_dev_init(struct hif_device_usb *hif_dev)
 static void ath9k_hif_usb_dev_deinit(struct hif_device_usb *hif_dev)
 {
 	ath9k_hif_usb_dealloc_urbs(hif_dev);
+	ath9k_hif_usb_free_rx_remain_skb(hif_dev);
 }