CVE-2026-23209

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

macvlan: fix error recovery in macvlan_common_newlink()

valis provided a nice repro to crash the kernel:

ip link add p1 type veth peer p2 ip link set address 00:00:00:00:00:20 dev p1 ip link set up dev p1 ip link set up dev p2

ip link add mv0 link p2 type macvlan mode source ip link add invalid% link p2 type macvlan mode source macaddr add 00:00:00:00:00:20

ping -c1 -I p1 1.2.3.4

He also gave a very detailed analysis:

The issue is triggered when a new macvlan link is created with MACVLAN_MODE_SOURCE mode and MACVLAN_MACADDR_ADD (or MACVLAN_MACADDR_SET) parameter, lower device already has a macvlan port and register_netdevice() called from macvlan_common_newlink() fails (e.g. because of the invalid link name).

In this case macvlan_hash_add_source is called from macvlan_change_sources() / macvlan_common_newlink():

This adds a reference to vlan to the ports vlan_source_hash using macvlan_source_entry.

vlan is a pointer to the priv data of the link that is being created.

When register_netdevice() fails, the error is returned from macvlan_newlink() to rtnl_newlink_create():

    if (ops->newlink)
            err = ops->newlink(dev, &params, extack);
    else
            err = register_netdevice(dev);
    if (err < 0) {
            free_netdev(dev);
            goto out;
    }

and free_netdev() is called, causing a kvfree() on the struct net_device that is still referenced in the source entry attached to the lower devices macvlan port.

Now all packets sent on the macvlan port with a matching source mac address will trigger a use-after-free in macvlan_forward_source().

</quote valis>

With all that, my fix is to make sure we call macvlan_flush_sources() regardless of @create value whenever goto destroy_macvlan_port; path is taken.

Many thanks to valis for following up on this issue.

Affected Software

References

• https://git.kernel.org/stable/c/11ba9f0dc865136174cb98834280fb21bbc950c7
• https://git.kernel.org/stable/c/5dae6b36a7cb7a4fcf4121b95e9ca7f96f816c8a
• https://git.kernel.org/stable/c/986967a162142710076782d5b93daab93a892980
• https://git.kernel.org/stable/c/c43d0e787cbba569ec9d11579ed370b50fab6c9c
• https://git.kernel.org/stable/c/cdedcd5aa3f3cb8b7ae0f87ab3a936d0bd583d66
• https://git.kernel.org/stable/c/da5c6b8ae47e414be47e5e04def15b25d5c962dc
• https://git.kernel.org/stable/c/f8db6475a83649689c087a8f52486fcc53e627e9