wifi: brcmfmac: Fix potential use-after-free issue when stopping watchdog task

commit c623b63 upstream.

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: 373c83a ("brcmfmac: stop watchdog before detach and free everything")
Fixes: a9ffda8 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: mszyprow

drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c

@@ -2475,8 +2475,9 @@ 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);
+		kthread_stop_put(bus->watchdog_tsk);
 		bus->watchdog_tsk = NULL;
 	}
 
@@ -4557,8 +4558,9 @@ 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);
+			kthread_stop_put(bus->watchdog_tsk);
 			bus->watchdog_tsk = NULL;
 		}