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 its 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 doesnt affect packets entering OVS datapath from network interfaces, because in this case CT metadata is populated from skb after the packet is already parsed.

Weakness

The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, in Java, if the programmer does not explicitly initialize a variable, then the code could produce a compile-time error (if the variable is local) or automatically initialize the variable to the default value for the variable’s type. In Perl, if explicit initialization is not performed, then a default value of undef is assigned, which is interpreted as 0, false, or an equivalent value depending on the context in which the variable is accessed.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/0b532f59437f688563e9c58bdc1436fefa46e3b5
• https://git.kernel.org/stable/c/431e9215576d7b728f3f53a704d237a520092120
• https://git.kernel.org/stable/c/483eb70f441e2df66ade78aa7217e6e4caadfef3
• https://git.kernel.org/stable/c/5ab6aecbede080b44b8e34720ab72050bf1e6982
• https://git.kernel.org/stable/c/6a51ac92bf35d34b4996d6eb67e2fe469f573b11
• https://git.kernel.org/stable/c/78741b4caae1e880368cb2f5110635f3ce45ecfd
• https://git.kernel.org/stable/c/7c988176b6c16c516474f6fceebe0f055af5eb56
• https://git.kernel.org/stable/c/9ec8b0ccadb908d92f7ee211a4eff05fd932f3f6
• https://git.kernel.org/stable/c/d73fb8bddf89503c9fae7c42e50d44c89909aad6
• https://git.kernel.org/stable/c/0b532f59437f688563e9c58bdc1436fefa46e3b5
• https://git.kernel.org/stable/c/431e9215576d7b728f3f53a704d237a520092120
• https://git.kernel.org/stable/c/483eb70f441e2df66ade78aa7217e6e4caadfef3
• https://git.kernel.org/stable/c/5ab6aecbede080b44b8e34720ab72050bf1e6982
• https://git.kernel.org/stable/c/6a51ac92bf35d34b4996d6eb67e2fe469f573b11
• https://git.kernel.org/stable/c/78741b4caae1e880368cb2f5110635f3ce45ecfd
• https://git.kernel.org/stable/c/7c988176b6c16c516474f6fceebe0f055af5eb56
• https://git.kernel.org/stable/c/9ec8b0ccadb908d92f7ee211a4eff05fd932f3f6
• https://git.kernel.org/stable/c/d73fb8bddf89503c9fae7c42e50d44c89909aad6
• https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html