media: mtk-jpeg: Fix use after free bug due to error path handling in mtk_jpeg_dec_device_run

[ Upstream commit 206c857dd17d4d026de85866f1b5f0969f2a109e ]

In mtk_jpeg_probe, &jpeg->job_timeout_work is bound with
mtk_jpeg_job_timeout_work.

In mtk_jpeg_dec_device_run, if error happens in
mtk_jpeg_set_dec_dst, it will finally start the worker while
mark the job as finished by invoking v4l2_m2m_job_finish.

There are two methods to trigger the bug. If we remove the
module, it which will call mtk_jpeg_remove to make cleanup.
The possible sequence is as follows, which will cause a
use-after-free bug.

CPU0                  CPU1
mtk_jpeg_dec_...    |
  start worker	    |
                    |mtk_jpeg_job_timeout_work
mtk_jpeg_remove     |
  v4l2_m2m_release  |
    kfree(m2m_dev); |
                    |
                    | v4l2_m2m_get_curr_priv
                    |   m2m_dev->curr_ctx //use

If we close the file descriptor, which will call mtk_jpeg_release,
it will have a similar sequence.

Fix this bug by starting timeout worker only if started jpegdec worker
successfully. Then v4l2_m2m_job_finish will only be called in
either mtk_jpeg_job_timeout_work or mtk_jpeg_dec_device_run.

Fixes: b2f0d2724b ("[media] vcodec: mediatek: Add Mediatek JPEG Decoder Driver")
Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: stable@vger.kernel.org
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/media/platform/mtk-jpeg/mtk_jpeg_core.c

@@ -977,13 +977,13 @@ static void mtk_jpeg_dec_device_run(void *priv)
 	if (ret < 0)
 		goto dec_end;
 
-	schedule_delayed_work(&jpeg->job_timeout_work,
-			      msecs_to_jiffies(MTK_JPEG_HW_TIMEOUT_MSEC));
-
 	mtk_jpeg_set_dec_src(ctx, &src_buf->vb2_buf, &bs);
 	if (mtk_jpeg_set_dec_dst(ctx, &jpeg_src_buf->dec_param, &dst_buf->vb2_buf, &fb))
 		goto dec_end;
 
+	schedule_delayed_work(&jpeg->job_timeout_work,
+			      msecs_to_jiffies(MTK_JPEG_HW_TIMEOUT_MSEC));
+
 	spin_lock_irqsave(&jpeg->hw_lock, flags);
 	mtk_jpeg_dec_reset(jpeg->reg_base);
 	mtk_jpeg_dec_set_config(jpeg->reg_base,