In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: L2CAP: Fix use-after-free in l2capunregisteruser

After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hcichandel"), l2capconndel() uses conn->lock to protect access to conn->users. However, l2capregisteruser() and l2capunregisteruser() don't use conn->lock, creating a race condition where these functions can access conn->users and conn->hchan concurrently with l2capconndel().

This can lead to use-after-free and list corruption bugs, as reported by syzbot.

Fix this by changing l2capregisteruser() and l2capunregisteruser() to use conn->lock instead of hcidevlock(), ensuring consistent locking for the l2capconn structure.