CVE-2024-38558

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

net: openvswitch: fix overwriting ct original tuple for ICMPv6

OVS_PACKET_CMD_EXECUTE has 3 main attributes:

- OVS_PACKET_ATTR_KEY - Packet metadata in a netlink format.

- OVS_PACKET_ATTR_PACKET - Binary packet content.

- OVS_PACKET_ATTR_ACTIONS - Actions to execute on the packet.

OVS_PACKET_ATTR_KEY is parsed first to populate sw_flow_key structure

with the metadata like conntrack state, input port, recirculation id,

etc. Then the packet itself gets parsed to populate the rest of the

keys from the packet headers.

Whenever the packet parsing code starts parsing the ICMPv6 header, it

first zeroes out fields in the key corresponding to Neighbor Discovery

information even if it is not an ND packet.

It is an 'ipv6.nd' field. However, the 'ipv6' is a union that shares

the space between 'nd' and 'ct_orig' that holds the original tuple

conntrack metadata parsed from the OVS_PACKET_ATTR_KEY.

ND packets should not normally have conntrack state, so it's fine to

share the space, but normal ICMPv6 Echo packets or maybe other types of

ICMPv6 can have the state attached and it should not be overwritten.

The issue results in all but the last 4 bytes of the destination

address being wiped from the original conntrack tuple leading to

incorrect packet matching and potentially executing wrong actions

in case this packet recirculates within the datapath or goes back

to userspace.

ND fields should not be accessed in non-ND packets, so not clearing

them should be fine. Executing memset() only for actual ND packets to

avoid the issue.

Initializing the whole thing before parsing is needed because ND packet

may not contain all the options.

The issue only affects the OVS_PACKET_CMD_EXECUTE path and doesn't

affect packets entering OVS datapath from network interfaces, because

in this case CT metadata is populated from skb after the packet is

already parsed.