CVE-2026-68296 (GCVE-0-2026-68296)

Vulnerability from cvelistv5 – Published: 2026-08-10 12:02 – Updated: 2026-08-17 05:02
VLAI
Title
net: gre: fix lltx regression for GRE tunnels with SEQ/CSUM
Summary
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.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 00d066a4d4edbe559ba6c35153da71d4b2b8a383 , < 9f948e9aede9678f4103457daf2bc9dd54c65a06 (git)
Affected: 00d066a4d4edbe559ba6c35153da71d4b2b8a383 , < 15a1c5f2ed2eeb3daad8d5766fd506aeda4710f3 (git)
Affected: 00d066a4d4edbe559ba6c35153da71d4b2b8a383 , < 2bffe379023512d280337c70faeb6a8cc435db5e (git)
Affected: 00d066a4d4edbe559ba6c35153da71d4b2b8a383 , < 675ed582c1aa4d919dd535490de08c015005c653 (git)
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Linux Linux Affected: 6.12
Unaffected: 0 , < 6.12 (semver)
Unaffected: 6.12.101 , ≤ 6.12.* (semver)
Unaffected: 6.18.42 , ≤ 6.18.* (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/ip_gre.c",
            "net/ipv6/ip6_gre.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "lessThan": "9f948e9aede9678f4103457daf2bc9dd54c65a06",
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          "vendor": "Linux",
          "versions": [
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              "versionType": "semver"
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              "versionType": "semver"
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              "operator": "OR"
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: gre: fix lltx regression for GRE tunnels with SEQ/CSUM\n\nBefore commit 00d066a4d4ed (\"netdev_features: convert NETIF_F_LLTX to\ndev-\u003elltx\"), NETIF_F_LLTX was set unconditionally in both\n__gre_tunnel_init() and ip6gre_tnl_init_features() alongside\nGRE_FEATURES:\n\n    dev-\u003efeatures |= GRE_FEATURES | NETIF_F_LLTX;\n\nWhen that commit converted NETIF_F_LLTX to the dev-\u003elltx flag, it\nplaced \u0027dev-\u003elltx = true\u0027 after the SEQ/CSUM early returns instead\nof before them. This causes GRE/GRETAP/ip6gre tunnels with SEQ or\nCSUM+encap to lose lockless TX, reintroducing _xmit_lock acquisition\naround their ndo_start_xmit. Since GRE xmit re-enters the stack via\nip_tunnel_xmit(), holding _xmit_lock risks ABBA deadlock with the\nunderlay device.\n\n  CPU0                        CPU1\n  ----                        ----\n  lock(\u0026qdisc_xmit_lock_key#6);\n                              lock(\u0026qdisc_xmit_lock_key#3);\n                              lock(\u0026qdisc_xmit_lock_key#6);\n  lock(\u0026qdisc_xmit_lock_key#3);\n\nFix by moving dev-\u003elltx = true before the early returns in both\nfunctions, restoring the original unconditional behavior."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:02:32.404Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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        },
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          "url": "https://git.kernel.org/stable/c/2bffe379023512d280337c70faeb6a8cc435db5e"
        },
        {
          "url": "https://git.kernel.org/stable/c/675ed582c1aa4d919dd535490de08c015005c653"
        }
      ],
      "title": "net: gre: fix lltx regression for GRE tunnels with SEQ/CSUM",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-68296",
    "datePublished": "2026-08-10T12:02:29.464Z",
    "dateReserved": "2026-07-30T09:28:09.380Z",
    "dateUpdated": "2026-08-17T05:02:32.404Z",
    "state": "PUBLISHED"
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: gre: fix lltx regression for GRE tunnels with SEQ/CSUM\n\nBefore commit 00d066a4d4ed (\"netdev_features: convert NETIF_F_LLTX to\ndev-\u003elltx\"), NETIF_F_LLTX was set unconditionally in both\n__gre_tunnel_init() and ip6gre_tnl_init_features() alongside\nGRE_FEATURES:\n\n    dev-\u003efeatures |= GRE_FEATURES | NETIF_F_LLTX;\n\nWhen that commit converted NETIF_F_LLTX to the dev-\u003elltx flag, it\nplaced \u0027dev-\u003elltx = true\u0027 after the SEQ/CSUM early returns instead\nof before them. This causes GRE/GRETAP/ip6gre tunnels with SEQ or\nCSUM+encap to lose lockless TX, reintroducing _xmit_lock acquisition\naround their ndo_start_xmit. Since GRE xmit re-enters the stack via\nip_tunnel_xmit(), holding _xmit_lock risks ABBA deadlock with the\nunderlay device.\n\n  CPU0                        CPU1\n  ----                        ----\n  lock(\u0026qdisc_xmit_lock_key#6);\n                              lock(\u0026qdisc_xmit_lock_key#3);\n                              lock(\u0026qdisc_xmit_lock_key#6);\n  lock(\u0026qdisc_xmit_lock_key#3);\n\nFix by moving dev-\u003elltx = true before the early returns in both\nfunctions, restoring the original unconditional behavior."
          }
        ],
        "id": "CVE-2026-68296",
        "lastModified": "2026-08-17T05:18:32.323",
        "metrics": {},
        "published": "2026-08-10T13:20:19.053",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "vulnStatus": "Received"
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-31T11:21:20+00:00",
      "cve": "CVE-2026-68296",
      "id": "CVE-2026-68296",
      "initial_release_date": "2026-08-10T00:00:00+00:00",
      "product_status:known_affected": "183",
      "product_status:known_not_affected": "94",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net: gre: fix lltx regression for GRE tunnels with SEQ/CSUM",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68296.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-15T01:36:51Z",
      "cve": "CVE-2026-68296",
      "id": "CVE-2026-68296",
      "initial_release_date": "2026-08-14T17:14:31Z",
      "product_status:known_affected": "29",
      "product_status:known_not_affected": "345",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-68296",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-68296.json",
      "version": "5"
    }
  }
}



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