net: ipv6: flowlabel: defer exclusive option free until RCU teardown

{
  "id": "c76f678fa8d75904f986dd8c8925586227ea1cfb61cb63c50479ad783b0e7f15",
  "url": "https://osv.dev/vulnerability/CVE-2026-31680",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net: ipv6: flowlabel: defer exclusive option free until RCU teardown",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net: ipv6: flowlabel: defer exclusive option free until RCU teardown `ip6fl_seq_show()` walks the global flowlabel hash under the seq-file RCU read-side lock and prints `fl->opt->opt_nflen` when an option block is present. Exclusive flowlabels currently free `fl->opt` as soon as `fl->users` drops to zero in `fl_release()`. However, the surrounding `struct ip6_flowlabel` remains visible in the global hash table until later garbage collection removes it and `fl_free_rcu()` finally tears it down. A concurrent `/proc/net/ip6_flowlabel` reader can therefore race that early `kfree()` and dereference freed option state, triggering a crash in `ip6fl_seq_show()`. Fix this by keeping `fl->opt` alive until `fl_free_rcu()`. That matches the lifetime already required for the enclosing flowlabel while readers can still reach it under RCU.",
    "evidence": "osv:CVE-2026-31680",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.253",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.203",
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          {
            "value": "6.19.12",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-31680",
      "aliases": [
        "CVE-2026-31680"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
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      "affected": [
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                {
                  "fixed": "4b6798024f7b2d535f3db1002c760143cdbd1bd3"
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                {
                  "fixed": "3c54b66c83fb8fcbde8e6a7bf90b65856e39f827"
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                {
                  "fixed": "5a6b15f861b7c1304949e3350d23490a5fe429fd"
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                {
                  "fixed": "6c7fbdb8ffde6413640de7cfbd7c976c353e89f8"
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                  "fixed": "9ca562bb8e66978b53028fa32b1a190708e6a091"
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          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31680.json"
          }
        },
        {
          "ranges": [
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              "type": "ECOSYSTEM",
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                  "introduced": "3.9.0"
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31680.json"
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      ],
      "modified": "2026-10-28T02:30:30.502329640Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-082556.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827",
        "https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a",
        "https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3",
        "https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4",
        "https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd",
        "https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8",
        "https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b",
        "https://git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31680.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31680",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31680.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-31680",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 497697,
  "published_at": "2026-04-25T08:46:56.807+00:00"
}