CVE-2026-81003: net/iucv: filter frames in afiucv_hs_rcv() by ingress device

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

net/iucv: filter frames in afiucvhsrcv() by ingress device

afiucvhsrcv() selects a socket from iucvsklist by matching four 8-byte name fields in the transport header alone. No check is made against the netdevice the frame arrived on.

This can cause a frame arriving on any netdev to be delivered to an AFIUCV socket. Three problems follow.

First, a frame arriving over HiperSockets can be delivered to a socket bound to the classic z/VM IUCV transport, which has iucv->hsdev == NULL. iucvsockbind() takes the classic path whenever the requested userid matches iucvuserid, even on a guest that also has a HiperSockets device carrying the same identifier. The child socket created by afiucvhscallbacksyn() for such a match inherits hsdev = NULL and transport = AFIUCVTRANSHIPER, so the first send() on it returns -ENODEV. The socket delivered to accept() is unusable.

Second, a frame arriving on one netdev can be delivered to a socket bound to a different IQD device. Which can lead to - Accept-queue exhaustion (DoS) - Attacker-controlled peer identity in the child socket - Data injection into existing sockets - Fabric noise on the IQD fabric, where bogus replies are sent - killing established connections

Third, all AFIUCV sockets live in initnet, as iucvsockalloc() calls skalloc(&initnet, ...). But even frames arriving on netdev devices in a namespace can be delivered to an IUCV socket. So a process in an unprivileged user and network namespace holding only the CAPNETRAW capability valid within that namespace can send a raw ETHPAFIUCV frame on its own lo device and have it matched against initnet sockets.

Fix all three by skipping any socket whose hsdev does not match the ingress device. A classic z/VM IUCV socket has hsdev == NULL; the ingress dev is never NULL, so classic sockets are skipped automatically. An unbound HIPER socket also has hsdev == NULL and is skipped. A bound HIPER socket is only reachable from the exact IQD device it was bound to. Because hsdev is always a device in initnet (iucvsockbind() scans foreachnetdevrcu(&initnet, ...) exclusively), a frame whose ingress device belongs to another namespace never matches any socket.

Note that AFIUCV over HiperSockets provides no per-connection authentication: no sequence numbers, no TLS, no nonce. The four name fields identifying a connection are exchanged in plaintext on the shared HiperSockets segment (VCHID). Any host on the same HiperSockets segment could spoof any frame type against an existing connection. That is a protocol-level property unchanged by this patch. The fix reduces the attack surface to peers present on the same HiperSockets segment.