[PATCH 5.16 0334/1017] media: em28xx: initialize refcount before kref_get

Greg Kroah-Hartman
2022-04-05T09:13:40Z

From: Dongliang Mu <mudongliangabcd@gmail.com>

[ 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>
---
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 b451ce3cb169..f3b56c065ee1 100644
--- a/drivers/media/usb/em28xx/em28xx-cards.c
+++ b/drivers/media/usb/em28xx/em28xx-cards.c
@@ -3936,6 +3936,8 @@ 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;
@@ -4036,6 +4038,8 @@ 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 &&
@@ -4090,12 +4094,8 @@ 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