CVE-2026-81003

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

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

afiucv_hs_rcv() selects a socket from iucv_sk_list by matching four 8-byte

name fields in the transport header alone. No check is made against the

net_device the frame arrived on.

This can cause a frame arriving on any netdev to be delivered to an AF_IUCV

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->hs_dev == NULL.

iucv_sock_bind() takes the classic path whenever the requested userid

matches iucv_userid, even on a guest that also has a HiperSockets device

carrying the same identifier. The child socket created by

afiucv_hs_callback_syn() for such a match inherits hs_dev = NULL and

transport = AF_IUCV_TRANS_HIPER, 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 AF_IUCV sockets live in init_net, as iucv_sock_alloc() calls

sk_alloc(&init_net, ...). 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 CAP_NET_RAW

capability valid within that namespace can send a raw ETH_P_AF_IUCV frame

on its own lo device and have it matched against init_net sockets.

Fix all three by skipping any socket whose hs_dev does not match the

ingress device. A classic z/VM IUCV socket has hs_dev == NULL; the ingress

dev is never NULL, so classic sockets are skipped automatically. An unbound

HIPER socket also has hs_dev == NULL and is skipped. A bound HIPER socket

is only reachable from the exact IQD device it was bound to. Because hs_dev

is always a device in init_net (iucv_sock_bind() scans

for_each_netdev_rcu(&init_net, ...) exclusively), a frame whose ingress

device belongs to another namespace never matches any socket.

Note that AF_IUCV 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.