CVE-2026-68393: Undefined Security Weakness

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

Bluetooth: hci_sync: extend conn_hash lookup critical sections

Using RCU-protected pointers outside the critical sections without refcount is incorrect and may result to UAF.

Extend critical section to cover both hci_conn_hash lookup and use of the returned conn.

Add surrounding rcu_read_lock() also when return value is not used, in preparation for RCU lockdep requirement to hci_lookup_le_connect().

This avoids concurrent deletion of the conn before we are done dereferencing it.

Also, make sure to hold hdev->lock when accessing hdev->accept_list.