GHSA-2XWR-GH6X-HM86

Vulnerability from github – Published: 2026-04-25 09:30 – Updated: 2026-04-27 15:30
VLAI?
Details

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.

Severity ?
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-31680"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-04-25T09:16:01Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: flowlabel: defer exclusive option free until RCU teardown\n\n`ip6fl_seq_show()` walks the global flowlabel hash under the seq-file\nRCU read-side lock and prints `fl-\u003eopt-\u003eopt_nflen` when an option block\nis present.\n\nExclusive flowlabels currently free `fl-\u003eopt` as soon as `fl-\u003eusers`\ndrops to zero in `fl_release()`. However, the surrounding\n`struct ip6_flowlabel` remains visible in the global hash table until\nlater garbage collection removes it and `fl_free_rcu()` finally tears it\ndown.\n\nA concurrent `/proc/net/ip6_flowlabel` reader can therefore race that\nearly `kfree()` and dereference freed option state, triggering a crash\nin `ip6fl_seq_show()`.\n\nFix this by keeping `fl-\u003eopt` alive until `fl_free_rcu()`. That matches\nthe lifetime already required for the enclosing flowlabel while readers\ncan still reach it under RCU.",
  "id": "GHSA-2xwr-gh6x-hm86",
  "modified": "2026-04-27T15:30:51Z",
  "published": "2026-04-25T09:30:28Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31680"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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