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:

<quote valis>

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 port's 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 device's 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.