# CVE-2026-68296: net: gre: fix lltx regression for GRE tunnels with SEQ/CSUM

Status: published. Published: 2026-08-10. Updated: 2026-11-06.

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);
                              lock(&qdisc_xmit_lock_key#6);
  lock(&qdisc_xmit_lock_key#3);

Fix by moving dev->lltx = true before the early returns in both
functions, restoring the original unconditional behavior.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 00d066a4d4edbe559ba6c35153da71d4b2b8a383; < 9f948e9aede9678f4103457daf2bc9dd54c65a06 (affected, git); ≥ 00d066a4d4edbe559ba6c35153da71d4b2b8a383; < 15a1c5f2ed2eeb3daad8d5766fd506aeda4710f3 (affected, git); ≥ 00d066a4d4edbe559ba6c35153da71d4b2b8a383; < 2bffe379023512d280337c70faeb6a8cc435db5e (affected, git); ≥ 00d066a4d4edbe559ba6c35153da71d4b2b8a383; < 675ed582c1aa4d919dd535490de08c015005c653 (affected, git). Source: CNA: Linux
- Linux / Linux: 6.12 (affected); ≥ 0; < 6.12 (unaffected, semver); ≥ 6.12.101; ≤ 6.12.* (unaffected, semver); ≥ 6.18.42; ≤ 6.18.* (unaffected, semver); ≥ 7.1.6; ≤ 7.1.* (unaffected, semver); ≥ 7.2; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.21% as of 2026-11-06; percentile 10.63%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/9f948e9aede9678f4103457daf2bc9dd54c65a06 (CNA: Linux)

- https://git.kernel.org/stable/c/15a1c5f2ed2eeb3daad8d5766fd506aeda4710f3 (CNA: Linux)

- https://git.kernel.org/stable/c/2bffe379023512d280337c70faeb6a8cc435db5e (CNA: Linux)

- https://git.kernel.org/stable/c/675ed582c1aa4d919dd535490de08c015005c653 (CNA: Linux)

- https://git.kernel.org/stable/c/15a1c5f2ed2eeb3daad8d5766fd506aeda4710f3 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/2bffe379023512d280337c70faeb6a8cc435db5e (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/675ed582c1aa4d919dd535490de08c015005c653 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/9f948e9aede9678f4103457daf2bc9dd54c65a06 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-68296; retrieved 2026-11-06; source updated 2026-11-06

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68296; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-68296; retrieved 2026-11-06; source updated Not reported

Revision: fd3e259e0aed914f51dd63bf232caff30e1cd2ee55f96943f880c345b85e1f34

Canonical: https://y2.dev/cve/CVE-2026-68296

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