[PATCH] media: dvbdev: fix uaf in dvb_remove_device()

[Jeffin Philip]

In dvb_remove_device(), dvb_media_device_free(), device_destroy()
and list_del() all dereference dvbdev regardless of its refcount.
Thus, if refcount for dvbdev is 1, it can be freed and we
operate on freed memory causing a UAF. Fix this by moving
dvb_device_put() at the end of dvb_remove_device() so dvbdev
members can be safely freed and assigned NULL when dvbdev is alive.

Reported-by: syzbot+37578f730d38898f4b74@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=37578f730d38898f4b74
Fixes: 0fc044b2b5e2 ("media: dvbdev: adopts refcnt to avoid UAF")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jeffin Philip <jeffinphilip14@xxxxxxxxx>
---
 drivers/media/dvb-core/dvbdev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbdev.c
index d753d329502a..9aa4b8fd7379 100644
--- a/drivers/media/dvb-core/dvbdev.c
+++ b/drivers/media/dvb-core/dvbdev.c
@@ -598,7 +598,6 @@ void dvb_remove_device(struct dvb_device *dvbdev)
 
 	down_write(&minor_rwsem);
 	dvb_minors[dvbdev->minor] = NULL;
-	dvb_device_put(dvbdev);
 	up_write(&minor_rwsem);
 
 	dvb_media_device_free(dvbdev);
@@ -606,6 +605,8 @@ void dvb_remove_device(struct dvb_device *dvbdev)
 	device_destroy(dvb_class, MKDEV(DVB_MAJOR, dvbdev->minor));
 
 	list_del(&dvbdev->list_head);
+
+	dvb_device_put(dvbdev);
 }
 EXPORT_SYMBOL(dvb_remove_device);
 
-- 
2.55.0