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

Type: advisorySource: Official CVE List1 source record

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.

Announced Source revision 1
Original source ↗

CVE-2026-31680

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-31680

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "d3aedd5ebd4b0b925b0bcda548066803e1318499",
        "lessThan": "4b6798024f7b2d535f3db1002c760143cdbd1bd3",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "d3aedd5ebd4b0b925b0bcda548066803e1318499",
        "lessThan": "3c54b66c83fb8fcbde8e6a7bf90b65856e39f827",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "d3aedd5ebd4b0b925b0bcda548066803e1318499",
        "lessThan": "5a6b15f861b7c1304949e3350d23490a5fe429fd",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "d3aedd5ebd4b0b925b0bcda548066803e1318499",
        "lessThan": "6c7fbdb8ffde6413640de7cfbd7c976c353e89f8",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "d3aedd5ebd4b0b925b0bcda548066803e1318499",
        "lessThan": "8027964931785cb73d520ac70a342a3dc16c249b",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "d3aedd5ebd4b0b925b0bcda548066803e1318499",
        "lessThan": "414726b69921fe6355ae453f5b35e68dd078342a",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "d3aedd5ebd4b0b925b0bcda548066803e1318499",
        "lessThan": "572ce62778519a7d4d1c15f55dd2e45a474133c4",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "d3aedd5ebd4b0b925b0bcda548066803e1318499",
        "lessThan": "9ca562bb8e66978b53028fa32b1a190708e6a091",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "net/ipv6/ip6_flowlabel.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "3.9"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "3.9",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.10.253",
        "versionType": "semver",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.15.203",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.168",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.134",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.81",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.22",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "6.19.12",
        "versionType": "semver",
        "lessThanOrEqual": "6.19.*"
      },
      {
        "status": "unaffected",
        "version": "7.0",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "net/ipv6/ip6_flowlabel.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-31680

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#39953 · Revision 1
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Publisher date
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