CVE-2024-49864: Concurrent Execution using Shared Resource with Improper Synchronization

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

rxrpc: Fix a race between socket set up and I/O thread creation

In rxrpc_open_socket(), it sets up the socket and then sets up the I/O thread that will handle it. This is a problem, however, as there's a gap between the two phases in which a packet may come into rxrpc_encap_rcv() from the UDP packet but we oops when trying to wake the not-yet created I/O thread.

As a quick fix, just make rxrpc_encap_rcv() discard the packet if there's no I/O thread yet.

A better, but more intrusive fix would perhaps be to rearrange things such that the socket creation is done by the I/O thread.