CVE-2025-68304

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

Bluetooth: hci_core: lookup hci_conn on RX path on protocol side

The hdev lock/lookup/unlock/use pattern in the packet RX path doesn't ensure hci_conn* is not concurrently modified/deleted. This locking appears to be leftover from before conn_hash started using RCU commit bf4c63252490b ("Bluetooth: convert conn hash to RCU") and not clear if it had purpose since then.

Currently, there are code paths that delete hci_conn* from elsewhere than the ordered hdev->workqueue where the RX work runs in. E.g. commit 5af1f84ed13a ("Bluetooth: hci_sync: Fix UAF on hci_abort_conn_sync") introduced some of these, and there probably were a few others before it. It's better to do the locking so that even if these run concurrently no UAF is possible.

Move the lookup of hci_conn and associated socket-specific conn to protocol recv handlers, and do them within a single critical section to cover hci_conn* usage and lookup.

syzkaller has reported a crash that appears to be this issue:

[Task hdev->workqueue]          [Task 2]
                                hci_disconnect_all_sync
l2cap_recv_acldata(hcon)
                                  hci_conn_get(hcon)
                                  hci_abort_conn_sync(hcon)
                                    hci_dev_lock
  hci_dev_lock
                                    hci_conn_del(hcon)
  v-------------------------------- hci_dev_unlock
                                  hci_conn_put(hcon)
  conn = hcon->l2cap_data (UAF)