CVE-2026-90232 — amt: Don't support cross-netns setup.

Affected: Linux

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

amt: Don't support cross-netns setup.

When a lower device is unregistered, amt_device_event() tries to unregister its upper AMT device, but it has two problems.

1. amt_lookup_upper_dev() looks up an upper device in the lower device's netns only

2. amt_device_event() unregisters a single upper device only

If AMT device is created on a lower device in another netns, removing the lower device triggers the splat below and gets stuck until all upper devices are removed. [0]

The cross-netns setup seems unintentional considering 1. and the following points:

* amt_link_setup() sets dev->netns_immutable to true * skb_scrub_packet() is not called in the fast path * iproute2 binary fails to find cross-netns lower device via link-netns: # ip -n ns1 link add amt0 link-netns ns2 type amt dev veth1 Cannot find device "veth1"

Instead of supporting it properly and preparing for per-netns netdev unreg, let's forbid cross-netns setup.

Note that the problem 2. needs a separate fix.

[0]: WARNING: net/core/dev.c:12518 at unregister_netdevice_many_notify+0x1cce/0x2250, CPU#48: ip/2031 Modules linked in: CPU: 48 UID: 0 PID: 2031 Comm: ip Not tainted 7.2.0-rc5+ #27 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 RIP: 0010:unregister_netdevice_many_notify (net/core/dev.c:12518) Code: 89 ef e8 d5 52 ae fe e9 d0 f4 ff ff 48 8d 3d f9 3b…

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CVE-2026-90232 — amt: Don't support cross-netns setup.