CVE-2026-99122: vsock/vmci: validate packet source for connected sockets

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

vsock/vmci: validate packet source for connected sockets

vmcitransportrecvstreamcb() looks up sockets first by the full source and destination tuple, then by destination only in the bound table. The fallback can select a non-listening socket without checking whether the packet came from its stored peer.

This was reproduced with two VMCI contexts. A RST from the context not stored in a TCPSYNSENT socket reset that socket after it was selected by the destination-only lookup.

VMCI can process notification packets in bottom-half context when the socket is not owned by user context, or defer packets to a workqueue. Use vsockchecksource() after taking the socket lock in the bottom-half path, and recheck after locksock() in the workqueue path. Listening sockets continue to accept packets from any source.

Reply with a RST addressed from the received packet before dropping a source that fails validation. This preserves the existing reset behavior for bound non-listening and concurrently closed sockets without directing the reset to a connected socket's stored peer.