[PATCH v2] wifi: mt76: mt7996: unlink TWT flow if the MCU rejects the agreement

mt7996_mac_add_twt_setup() links a new flow into dev->twt_list before
asking the MCU to add the agreement, but exits without unlinking the flow
if the request fails. The flow-ID and table masks are only committed
after MCU success, so the still-linked flow is invisible to the
mask-gated teardown paths.

If the station retries the setup, the same slot is cleared and its
embedded list node reinitialized while it is still linked, corrupting
dev->twt_list. If the station disassociates instead, teardown skips the
flow and station storage can be freed while the node remains linked. A
later scheduling or debugfs twt_stats walk can then dereference the
freed flow, resulting in a use-after-free.

Unlink the flow when the MCU rejects the agreement. This restores the
list to its pre-request state while leaving the unchanged mask and
agreement accounting untouched.

Fixes: 98686cd21624 ("wifi: mt76: mt7996: add driver for MediaTek Wi-Fi 7 (802.11be) devices")
Cc: [email protected]
Link: https://lore.kernel.org/all/[email protected]/
Assisted-by: Codex:gpt-5.6-sol
Assisted-by: Kimi:K3
Signed-off-by: Zhao Li <[email protected]>
---
Changes in v2:
- Rebase onto wireless/main commit 2812e64e1575.
- Send mt7996 as a standalone patch; mt7915 is fixed by commit
  16a04441eab0 ("wifi: mt76: mt7915: unlink TWT flow if the MCU rejects
  the agreement").
- Use list_del() to match the accepted mt7915 fix.
---
 drivers/net/wireless/mediatek/mt76/mt7996/mac.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
index 0eebc8182ca9..4d3829e4220d 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
@@ -3207,8 +3207,10 @@ void mt7996_mac_add_twt_setup(struct ieee80211_hw *hw,
 	flow->tsf = le64_to_cpu(twt_agrt->twt);
 
 	if (mt7996_mcu_twt_agrt_update(dev, &msta->vif->deflink, flow,
-				       MCU_TWT_AGRT_ADD))
+				       MCU_TWT_AGRT_ADD)) {
+		list_del(&flow->list);
 		goto unlock;
+	}
 
 	setup_cmd = TWT_SETUP_CMD_ACCEPT;
 	dev->twt.table_mask |= BIT(table_id);
-- 
2.50.1 (Apple Git-155)