CVE-2024-35973

/// Technical description

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

geneve: fix header validation in geneve[6]_xmit_skb

syzbot is able to trigger an uninit-value in geneve_xmit() [1]

Problem : While most ip tunnel helpers (like ip_tunnel_get_dsfield())

uses skb_protocol(skb, true), pskb_inet_may_pull() is only using

skb->protocol.

If anything else than ETH_P_IPV6 or ETH_P_IP is found in skb->protocol,

pskb_inet_may_pull() does nothing at all.

If a vlan tag was provided by the caller (af_packet in the syzbot case),

the network header might not point to the correct location, and skb

linear part could be smaller than expected.

Add skb_vlan_inet_prepare() to perform a complete mac validation.

Use this in geneve for the moment, I suspect we need to adopt this

more broadly.

v4 - Jakub reported v3 broke l2_tos_ttl_inherit.sh selftest

- Only call __vlan_get_protocol() for vlan types.

v2,v3 - Addressed Sabrina comments on v1 and v2

[1]

BUG: KMSAN: uninit-value in geneve_xmit_skb d

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References