[PATCH ath-next 3/6] wifi: ath12k: fix stale tail_msdu pointer returned from mpdu_pop

[Kang Yang <kang.yang@oss.qualcomm.com>]

ath12k_wifi7_dp_rx_mon_mpdu_pop() assigns *tail_msdu from the loop
cursor msdu at function exit. That cursor reflects the state of the
last msdu_list entry processed, not the end of the accumulated MSDU
chain: on next_msdu paths (invalid skb, drop_mpdu, first-MSDU rx_desc
invalid) it is set to NULL, and on the set_pktlen failure path it
becomes a dangling pointer to a freed skb. When these occur on the
final iteration, callers see head_msdu populated with a valid chain
while tail_msdu is NULL or points to freed memory.

The chain end is already tracked by the local variable last, which is
updated only after each MSDU has been validated and linked. Use it as
the source for tail_msdu so head_msdu and tail_msdu are either both
NULL or both point into the same live chain.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c7-00108-QCAHMTSWPL_V1.0_V2.0_SILICONZ_UPSTREAM-3

Fixes: 72bfbf19b7da ("wifi: ath12k: add support to reap and process mon dest ring")
Signed-off-by: Kang Yang <kang.yang@oss.qualcomm.com>
---
 drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c b/drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c
index 08f2fba3e680..8fca777041d1 100644
--- a/drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c
+++ b/drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c
@@ -2802,7 +2802,7 @@ ath12k_wifi7_dp_rx_mon_mpdu_pop(struct ath12k *ar, int mac_id,
 	if (last)
 		last->next = NULL;
 
-	*tail_msdu = msdu;
+	*tail_msdu = last;
 
 	if (msdu_cnt == 0)
 		*npackets = 1;
-- 
2.34.1