[PATCH] media: em28xx: fix use-after-free of dev_next->devlist on disconnect

[Jiangong . Han]

When a device with has_dual_ts=1 is probed and the is_audio_only path
is taken, both dev and dev->dev_next are added to the global
em28xx_devlist via em28xx_init_extension(). However, during disconnect,
em28xx_close_extension(dev) only calls list_del(&dev->devlist), leaving
dev->dev_next->devlist still linked in the global list. When dev_next is
subsequently freed via kref_put(), its devlist entry becomes a dangling
pointer in em28xx_devlist. The next device probe that calls
em28xx_init_extension() triggers a list corruption BUG when list_add_tail
detects the freed node.

This bug was exposed by commit a368ecde8a50 ("USB: core: Fix duplicate
endpoint bug by clearing reserved bits in the descriptor") which clears
reserved bits in bEndpointAddress during endpoint parsing. This causes
fuzzed endpoint addresses like 0xf3 to be normalized to 0x83, which
em28xx interprets as a vendor audio endpoint, enabling the
is_audio_only + has_dual_ts code path that was previously unreachable
with such descriptors.

Fix this by removing dev->dev_next->devlist from the global list in
em28xx_close_extension() before the device is freed.

Fixes: f410b4093fdd ("media: em28xx: split up em28xx_dvb_init to reduce stack size")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: syzbot+99d6c66dbbc484f50e1c@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=99d6c66dbbc484f50e1c
Signed-off-by: Jiangong.Han <jiangong.han@xxxxxxxxxxxxx>
---
 drivers/media/usb/em28xx/em28xx-core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/media/usb/em28xx/em28xx-core.c b/drivers/media/usb/em28xx/em28xx-core.c
index 5bbb082dbed9..3d6b196b8483 100644
--- a/drivers/media/usb/em28xx/em28xx-core.c
+++ b/drivers/media/usb/em28xx/em28xx-core.c
@@ -1265,6 +1265,8 @@ void em28xx_close_extension(struct em28xx *dev)
 			ops->fini(dev);
 		}
 	}
+	if (dev->dev_next)
+		list_del(&dev->dev_next->devlist);
 	list_del(&dev->devlist);
 	mutex_unlock(&em28xx_devlist_mutex);
 }
-- 
2.37.3