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 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, ¶ms, 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().
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.