[PATCH v3] wifi: rtw88: usb: fix memory leaks on USB write failures

[luka.gejak@linux.dev]

From: Luka Gejak <luka.gejak@linux.dev>

When rtw_usb_write_port() fails to submit a USB Request Block (URB)
(e.g., due to device disconnect or ENOMEM), the completion callback is
never executed.

Currently, the driver ignores the return value of rtw_usb_write_port()
in rtw_usb_write_data() and rtw_usb_tx_agg_skb(). Because these
functions rely on the completion callback to free the socket buffers
(skbs) and the transaction control block (txcb), a submission failure
results in:
1. A memory leak of the allocated skb in rtw_usb_write_data().
2. A memory leak of the txcb structure and all aggregated skbs in
   rtw_usb_tx_agg_skb().

Fix this by checking the return value of rtw_usb_write_port(). If it
fails, explicitly free the skb in rtw_usb_write_data(), and properly
purge the tx_ack_queue and free the txcb in rtw_usb_tx_agg_skb().

The issue was discovered in practice during device disconnect/reconnect
scenarios and memory pressure conditions. Tested by verifying normal TX
operation continues after the fix without regressions.

Fixes: a82dfd33d123 ("wifi: rtw88: Add common USB chip support")
Cc: stable@vger.kernel.org
Tested-by: Luka Gejak <luka.gejak@linux.dev>
Signed-off-by: Luka Gejak <luka.gejak@linux.dev>
---
Changes in v3:
 - Updated the Fixes tag to the commit that introduced USB support.
Changes in v2:
 - Use ret = rtw_usb_write_port(...); style, and check by next line (in
   rtw_usb_tx_agg_skb)
 - Remove unnecessary comment
 - Use ieee80211_purge_tx_queue() instead of skb_queue_purge()
 - Add testing details to commit message

 drivers/net/wireless/realtek/rtw88/usb.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/usb.c b/drivers/net/wireless/realtek/rtw88/usb.c
index 718940ebba31..1bb922cc2928 100644
--- a/drivers/net/wireless/realtek/rtw88/usb.c
+++ b/drivers/net/wireless/realtek/rtw88/usb.c
@@ -399,6 +399,7 @@ static bool rtw_usb_tx_agg_skb(struct rtw_usb *rtwusb, struct sk_buff_head *list
 	int agg_num = 0;
 	unsigned int align_next = 0;
 	u8 qsel;
+	int ret;
 
 	if (skb_queue_empty(list))
 		return false;
@@ -456,7 +457,13 @@ static bool rtw_usb_tx_agg_skb(struct rtw_usb *rtwusb, struct sk_buff_head *list
 	tx_desc = (struct rtw_tx_desc *)skb_head->data;
 	qsel = le32_get_bits(tx_desc->w1, RTW_TX_DESC_W1_QSEL);
 
-	rtw_usb_write_port(rtwdev, qsel, skb_head, rtw_usb_write_port_tx_complete, txcb);
+	ret = rtw_usb_write_port(rtwdev, qsel, skb_head,
+			         rtw_usb_write_port_tx_complete, txcb);
+	if (ret) {
+		ieee80211_purge_tx_queue(rtwdev->hw, &txcb->tx_ack_queue);
+		kfree(txcb);
+		return false;
+	}
 
 	return true;
 }
@@ -518,8 +525,10 @@ static int rtw_usb_write_data(struct rtw_dev *rtwdev,
 
 	ret = rtw_usb_write_port(rtwdev, qsel, skb,
 				 rtw_usb_write_port_complete, skb);
-	if (unlikely(ret))
+	if (unlikely(ret)) {
 		rtw_err(rtwdev, "failed to do USB write, ret=%d\n", ret);
+		dev_kfree_skb_any(skb);
+	}
 
 	return ret;
 }
-- 
2.54.0