media: saa7134: fix use after free bug in saa7134_finidev due to race condition

In saa7134_initdev, it will call saa7134_hwinit1. There are three
function invoking here: saa7134_video_init1, saa7134_ts_init1
and saa7134_vbi_init1.

All of them will init a timer with same function. Take
saa7134_video_init1 as an example. It'll bound &dev->video_q.timeout
with saa7134_buffer_timeout.

In buffer_activate, the timer funtcion is started.

If we remove the module or device which will call saa7134_finidev
to make cleanup, there may be a unfinished work. The
possible sequence is as follows, which will cause a
typical UAF bug.

Fix it by canceling the timer works accordingly before cleanup in
saa7134_finidev.

CPU0                  CPU1

                    |saa7134_buffer_timeout
saa7134_finidev     |
  kfree(dev);       |
                    |
                    | saa7134_buffer_next
                    | //use dev

Fixes: 1e7126b4 ("media: saa7134: Convert timers to use timer_setup()")
Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

drivers/media/pci/saa7134/saa7134-ts.c

@@ -300,6 +300,7 @@ int saa7134_ts_start(struct saa7134_dev *dev)
 
 int saa7134_ts_fini(struct saa7134_dev *dev)
 {
+	del_timer_sync(&dev->ts_q.timeout);
 	saa7134_pgtable_free(dev->pci, &dev->ts_q.pt);
 	return 0;
 }

drivers/media/pci/saa7134/saa7134-vbi.c

@@ -185,6 +185,7 @@ int saa7134_vbi_init1(struct saa7134_dev *dev)
 int saa7134_vbi_fini(struct saa7134_dev *dev)
 {
 	/* nothing */
+	del_timer_sync(&dev->vbi_q.timeout);
 	return 0;
 }
 

drivers/media/pci/saa7134/saa7134-video.c

@@ -1743,6 +1743,7 @@ int saa7134_video_init1(struct saa7134_dev *dev)
 
 void saa7134_video_fini(struct saa7134_dev *dev)
 {
+	del_timer_sync(&dev->video_q.timeout);
 	/* free stuff */
 	saa7134_pgtable_free(dev->pci, &dev->video_q.pt);
 	saa7134_pgtable_free(dev->pci, &dev->vbi_q.pt);