CVE-2026-68296

Technical Description

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

net: gre: fix lltx regression for GRE tunnels with SEQ/CSUM

Before commit 00d066a4d4ed ("netdev_features: convert NETIF_F_LLTX to

dev->lltx"), NETIF_F_LLTX was set unconditionally in both

__gre_tunnel_init() and ip6gre_tnl_init_features() alongside

GRE_FEATURES:

dev->features |= GRE_FEATURES | NETIF_F_LLTX;

When that commit converted NETIF_F_LLTX to the dev->lltx flag, it

placed 'dev->lltx = true' after the SEQ/CSUM early returns instead

of before them. This causes GRE/GRETAP/ip6gre tunnels with SEQ or

CSUM+encap to lose lockless TX, reintroducing _xmit_lock acquisition

around their ndo_start_xmit. Since GRE xmit re-enters the stack via

ip_tunnel_xmit(), holding _xmit_lock risks ABBA deadlock with the

underlay device.

CPU0 CPU1

---- ----

lock(&qdisc_xmit_lock_key#6);

lock(&qdisc_xmit_lock_key#3);

loc

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