CVE-2026-81003

Summary

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/dfac2936b83be00035ae176f8252e1c1e1de9207
• https://git.kernel.org/stable/c/8e3763f1ccac3fc395f9af2b87114c023ced8a3f
• https://git.kernel.org/stable/c/a7f0130a091724e69827ab58e74777a88747e892
• https://git.kernel.org/stable/c/80230a18c164a4b5bbc048fe2768b219ac17bc5a

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