FAILED: patch "[PATCH] wifi: wcn36xx: Fix potential use-after-free in TX ack timer" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x d9be5e75530772fc31637070d51e5717d6aeaa2a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026092259-deface-ethics-a18f@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d9be5e75530772fc31637070d51e5717d6aeaa2a Mon Sep 17 00:00:00 2001
From: Fan Wu <[email protected]>
Date: Thu, 10 Sep 2026 02:09:07 +0000
Subject: [PATCH] wifi: wcn36xx: Fix potential use-after-free in TX ack timer
teardown

wcn36xx_dxe_deinit() tears down the TX ack timer with timer_delete(), which only dequeues the timer and does not wait for a callback that is already executing; the preceding free_irq() calls synchronize the interrupt handlers only. The callback, wcn36xx_dxe_tx_timer(), can therefore be running past the teardown and use the wcn freed along with the ieee80211_hw in wcn36xx_remove(): it takes wcn->dxe_lock, reads wcn->tx_ack_skb and passes wcn->hw to ieee80211_tx_status_irqsafe().

Fix this by using timer_shutdown_sync(), which waits for a running callback and also prevents the timer from being rearmed again. The timer is set up again by wcn36xx_dxe_init() on the next start, so the start/stop cycle is unaffected.

This issue was found by an in-house static analysis tool.

index 44020ec265fb..801f1218ef89 100644
@@ -1055,7 +1055,7 @@ void wcn36xx_dxe_deinit(struct wcn36xx *wcn)
 
 	free_irq(wcn->tx_irq, wcn);
 	free_irq(wcn->rx_irq, wcn);
-	timer_delete(&wcn->tx_ack_timer);
+	timer_shutdown_sync(&wcn->tx_ack_timer);
 
 	if (wcn->tx_ack_skb) {
 		ieee80211_tx_status_irqsafe(wcn->hw, wcn->tx_ack_skb);

From: Fan Wu <[email protected]>

[ Upstream commit d9be5e75530772fc31637070d51e5717d6aeaa2a ]

wcn36xx_dxe_deinit() tears down the TX ack timer with timer_delete(), which only dequeues the timer and does not wait for a callback that is already executing; the preceding free_irq() calls synchronize the interrupt handlers only. The callback, wcn36xx_dxe_tx_timer(), can therefore be running past the teardown and use the wcn freed along with the ieee80211_hw in wcn36xx_remove(): it takes wcn->dxe_lock, reads wcn->tx_ack_skb and passes wcn->hw to ieee80211_tx_status_irqsafe().

Fix this by using timer_shutdown_sync(), which waits for a running callback and also prevents the timer from being rearmed again. The timer is set up again by wcn36xx_dxe_init() on the next start, so the start/stop cycle is unaffected.

This issue was found by an in-house static analysis tool.

---
 drivers/net/wireless/ath/wcn36xx/dxe.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index e1a35c2eadb6c..f3d850edbdbc7 100644
@@ -1007,7 +1007,7 @@ void wcn36xx_dxe_deinit(struct wcn36xx *wcn)
 
 	free_irq(wcn->tx_irq, wcn);
 	free_irq(wcn->rx_irq, wcn);
-	del_timer(&wcn->tx_ack_timer);
+	timer_shutdown_sync(&wcn->tx_ack_timer);
 
 	if (wcn->tx_ack_skb) {
 		ieee80211_tx_status_irqsafe(wcn->hw, wcn->tx_ack_skb);

2.53.0