[PATCH 6.1.y] media: s5p-mfc: use timer_shutdown_sync() for the self-rearming watchdog

[Sasha Levin <sashal@kernel.org>]

From: Fan Wu <fanwu01@zju.edu.cn>

[ Upstream commit 63069b5917cba2e15b1a78b3f4ff99e45102c56f ]

The MFC watchdog timer (s5p_mfc_watchdog) is self-rearming: every
callback re-arms itself with add_timer() and, on a timeout, schedules
watchdog_work. s5p_mfc_remove() tears this down with timer_delete_sync()
followed by flush_work().

timer_delete_sync() dequeues the timer and waits for a callback that is
already running, but it does not prevent a subsequent re-arm. Because the
watchdog callback re-arms via add_timer(), this is the wrong shutdown
primitive: once the wait returns nothing guarantees a just-queued re-arm
will not fire later, dereferencing dev (clock on/off, deinit_hw,
load_firmware, init_hw) after video_unregister_device(), DMA teardown and
s5p_mfc_final_pm() have run, a potential use-after-free.

Use timer_shutdown_sync(), which puts the timer into a shutdown state so
that any add_timer()/mod_timer() from the callback becomes a no-op and no
later firing is possible. Switch flush_work() to cancel_work_sync() so any
watchdog_work that was already queued before the timer was stopped is
cancelled rather than allowed to run to completion against the torn-down
device.

This issue was found by an in-house static analysis tool. No runtime
reproducer is available.

Fixes: af9357467810 ("[media] MFC: Add MFC 5.1 V4L2 driver")
Cc: stable@vger.kernel.org
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
[ sashal: adapted the timer replacement to the existing del_timer_sync() call instead of timer_delete_sync() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c b/drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c
index 007c7dbee0377..58479d2a69fa0 100644
--- a/drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c
+++ b/drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c
@@ -1440,8 +1440,8 @@ static int s5p_mfc_remove(struct platform_device *pdev)
 	}
 	mutex_unlock(&dev->mfc_mutex);
 
-	del_timer_sync(&dev->watchdog_timer);
-	flush_work(&dev->watchdog_work);
+	timer_shutdown_sync(&dev->watchdog_timer);
+	cancel_work_sync(&dev->watchdog_work);
 
 	video_unregister_device(dev->vfd_enc);
 	video_unregister_device(dev->vfd_dec);
-- 
2.53.0