[PATCH 5.15.y] wifi: brcmfmac: Fix potential use-after-free issue when stopping watchdog task

[Sasha Levin <sashal@kernel.org>]

From: Marek Szyprowski <m.szyprowski@samsung.com>

[ Upstream commit c623b63580880cc742255eaed3d79804c1b91143 ]

Watchdog task might end between send_sig() and kthread_stop() calls, what
results in the use-after-free issue. Fix this by increasing watchdog task
reference count before calling send_sig() and dropping it by switching to
kthread_stop_put().

Cc: stable@vger.kernel.org
Fixes: 373c83a801f1 ("brcmfmac: stop watchdog before detach and free everything")
Fixes: a9ffda88be74 ("brcm80211: fmac: abstract bus_stop interface function pointer")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://patch.msgid.link/20260416093339.2066829-1-m.szyprowski@samsung.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
[ replaced kthread_stop_put() with open-coded kthread_stop() + put_task_struct() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c
index 5006aa8317513..76b2953725c2d 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c
@@ -2474,8 +2474,10 @@ static void brcmf_sdio_bus_stop(struct device *dev)
 	brcmf_dbg(TRACE, "Enter\n");
 
 	if (bus->watchdog_tsk) {
+		get_task_struct(bus->watchdog_tsk);
 		send_sig(SIGTERM, bus->watchdog_tsk, 1);
 		kthread_stop(bus->watchdog_tsk);
+		put_task_struct(bus->watchdog_tsk);
 		bus->watchdog_tsk = NULL;
 	}
 
@@ -4549,8 +4551,10 @@ void brcmf_sdio_remove(struct brcmf_sdio *bus)
 	if (bus) {
 		/* Stop watchdog task */
 		if (bus->watchdog_tsk) {
+			get_task_struct(bus->watchdog_tsk);
 			send_sig(SIGTERM, bus->watchdog_tsk, 1);
 			kthread_stop(bus->watchdog_tsk);
+			put_task_struct(bus->watchdog_tsk);
 			bus->watchdog_tsk = NULL;
 		}
 
-- 
2.53.0