media: em28xx: initialize refcount before kref_get

[ 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@googlegroups.com>
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
index ebc430b..c415b1d 100644 (file)
--- a/drivers/media/usb/em28xx/em28xx-cards.c
+++ b/drivers/media/usb/em28xx/em28xx-cards.c
@@ -3931,6 +3931,8 @@ 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;
@@ -4031,6 +4033,8 @@ 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 &&
@@ -4085,12 +4089,8 @@ 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);
 
        /*