[PATCH 5.4 127/475] media: em28xx: initialize refcount before kref_get

[Greg Kroah-Hartman]

From: Dongliang Mu <mudongliangabcd@xxxxxxxxx>

[ Upstream commit c08eadca1bdfa099e20a32f8fa4b52b2f672236d ]

The commit 47677e51e2a4("[media] em28xx: Only deallocate struct
em28xx after finishing all extensions") adds kref_get to many init
functions (e.g., em28xx_audio_init). However, kref_init is called too
late in em28xx_usb_probe, since em28xx_init_dev before will invoke
those init functions and call kref_get function. Then refcount bug
occurs in my local syzkaller instance.

Fix it by moving kref_init before em28xx_init_dev. This issue occurs
not only in dev but also dev->dev_next.

Fixes: 47677e51e2a4 ("[media] em28xx: Only deallocate struct em28xx after finishing all extensions")
Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/media/usb/em28xx/em28xx-cards.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
index bfca9d0a1fe1..885ccb840ab0 100644
--- a/drivers/media/usb/em28xx/em28xx-cards.c
+++ b/drivers/media/usb/em28xx/em28xx-cards.c
@@ -3821,6 +3821,8 @@ static int em28xx_usb_probe(struct usb_interface *intf,
 		goto err_free;
 	}
 
+	kref_init(&dev->ref);
+
 	dev->devno = nr;
 	dev->model = id->driver_info;
 	dev->alt   = -1;
@@ -3921,6 +3923,8 @@ static int em28xx_usb_probe(struct usb_interface *intf,
 	}
 
 	if (dev->board.has_dual_ts && em28xx_duplicate_dev(dev) == 0) {
+		kref_init(&dev->dev_next->ref);
+
 		dev->dev_next->ts = SECONDARY_TS;
 		dev->dev_next->alt   = -1;
 		dev->dev_next->is_audio_only = has_vendor_audio &&
@@ -3975,12 +3979,8 @@ static int em28xx_usb_probe(struct usb_interface *intf,
 			em28xx_write_reg(dev, 0x0b, 0x82);
 			mdelay(100);
 		}
-
-		kref_init(&dev->dev_next->ref);
 	}
 
-	kref_init(&dev->ref);
-
 	request_modules(dev);
 
 	/*
-- 
2.34.1