CVE-2025-21858

/// Technical description

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

geneve: Fix use-after-free in geneve_find_dev().

syzkaller reported a use-after-free in geneve_find_dev() [0]

without repro.

geneve_configure() links struct geneve_dev.next to

net_generic(net, geneve_net_id)->geneve_list.

The net here could differ from dev_net(dev) if IFLA_NET_NS_PID,

IFLA_NET_NS_FD, or IFLA_TARGET_NETNSID is set.

When dev_net(dev) is dismantled, geneve_exit_batch_rtnl() finally

calls unregister_netdevice_queue() for each dev in the netns,

and later the dev is freed.

However, its geneve_dev.next is still linked to the backend UDP

socket netns.

Then, use-after-free will occur when another geneve dev is created

in the netns.

Let's call geneve_dellink() instead in geneve_destroy_tunnels().

[0]:

BUG: KASAN: slab-use-after-free in geneve_find_dev drivers/net/geneve.c:1295 [inline]

BUG: KASAN: slab-use-after-free in geneve_configure+0x234/0x858 drivers/net/geneve.c:1343

Read of size 2 at addr ffff00

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References