AZL-72649

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

Bluetooth: hcicore: lookup hciconn on RX path on protocol side

The hdev lock/lookup/unlock/use pattern in the packet RX path doesn't ensure hciconn* is not concurrently modified/deleted. This locking appears to be leftover from before connhash 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 hciconn* from elsewhere than the ordered hdev->workqueue where the RX work runs in. E.g. commit 5af1f84ed13a ("Bluetooth: hcisync: Fix UAF on hciabortconn_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 hciconn and associated socket-specific conn to protocol recv handlers, and do them within a single critical section to cover hciconn* 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)