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sched/fair: Fix zero_vruntime tracking fix

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix zero_vruntime tracking fix John reported that stress-ng-yield could make his machine unhappy and managed to bisect it to commit b3d99f43c72b ("sched/fair: Fix zero_vruntime tracking"). The combination of yield and that commit was specific enough to hypothesize the following scenario: Suppose we have 2 runnable tasks, both doing yield. Then one will be eligible and one will not be, because the average position must be in between these two entities. Therefore, the runnable task will be eligible, and be promoted a full slice (all the tasks do is yield after all). This causes it to jump over the other task and now the other task is eligible and current is no longer. So we schedule. Since we are runnable, there is no {de,en}queue. All we have is the __{en,de}queue_entity() from {put_prev,set_next}_task(). But per the fingered commit, those two no longer move zero_vruntime. All that moves zero_vruntime are tick and full {de,en}queue. This means, that if the two tasks playing leapfrog can reach the critical speed to reach the overflow point inside one tick's worth of time, we're up a creek. Additionally, when multiple cgroups are involved, there is no guarantee the tick will in fact hit every cgroup in a timely manner. Statistically speaking it will, but that same statistics does not rule out the possibility of one cgroup not getting a tick for a significant amount of time -- however unlikely. Theref

Products
Kernel
Affected versions
Not specified
Fixed versions
6.12.81, 6.18.22, 6.19.12
CVEs
CVE-2026-43323
Confirmed fixed CVEs
Not specified
Updated in this feed
8 Nov 2026, 00:40 UTC · Revision 1

Source evidence

sched/fair: Fix zero_vruntime tracking fix

core-osv · Original source

Published 8 May 2026, 13:31 UTC

In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix zero_vruntime tracking fix John reported that stress-ng-yield could make his machine unhappy and managed to bisect it to commit b3d99f43c72b ("sched/fair: Fix zero_vruntime tracking"). The combination of yield and that commit was specific enough to hypothesize the following scenario: Suppose we have 2 runnable tasks, both doing yield. Then one will be eligible and one will not be, because the average position must be in between these two entities. Therefore, the runnable task will be eligible, and be promoted a full slice (all the tasks do is yield after all). This causes it to jump over the other task and now the other task is eligible and current is no longer. So we schedule. Since we are runnable, there is no {de,en}queue. All we have is the __{en,de}queue_entity() from {put_prev,set_next}_task(). But per the fingered commit, those two no longer move zero_vruntime. All that moves zero_vruntime are tick and full {de,en}queue. This means, that if the two tasks playing leapfrog can reach the critical speed to reach the overflow point inside one tick's worth of time, we're up a creek. Additionally, when multiple cgroups are involved, there is no guarantee the tick will in fact hit every cgroup in a timely manner. Statistically speaking it will, but that same statistics does not rule out the possibility of one cgroup not getting a tick for a significant amount of time -- however unlikely. Theref

osv:CVE-2026-43323

Kernel

Fixed versions: 6.12.81, 6.18.22, 6.19.12

Complete source record
{
  "id": "3232c5deec734200b4977a898c69d086b22b864a1fcb5b8e3137979eacc573f7",
  "url": "https://osv.dev/vulnerability/CVE-2026-43323",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "sched/fair: Fix zero_vruntime tracking fix",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix zero_vruntime tracking fix John reported that stress-ng-yield could make his machine unhappy and managed to bisect it to commit b3d99f43c72b (\"sched/fair: Fix zero_vruntime tracking\"). The combination of yield and that commit was specific enough to hypothesize the following scenario: Suppose we have 2 runnable tasks, both doing yield. Then one will be eligible and one will not be, because the average position must be in between these two entities. Therefore, the runnable task will be eligible, and be promoted a full slice (all the tasks do is yield after all). This causes it to jump over the other task and now the other task is eligible and current is no longer. So we schedule. Since we are runnable, there is no {de,en}queue. All we have is the __{en,de}queue_entity() from {put_prev,set_next}_task(). But per the fingered commit, those two no longer move zero_vruntime. All that moves zero_vruntime are tick and full {de,en}queue. This means, that if the two tasks playing leapfrog can reach the critical speed to reach the overflow point inside one tick's worth of time, we're up a creek. Additionally, when multiple cgroups are involved, there is no guarantee the tick will in fact hit every cgroup in a timely manner. Statistically speaking it will, but that same statistics does not rule out the possibility of one cgroup not getting a tick for a significant amount of time -- however unlikely. Theref",
    "evidence": "osv:CVE-2026-43323",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.81",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.22",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.12",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-43323",
      "aliases": [
        "CVE-2026-43323"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                },
                {
                  "fixed": "c089147074ed96ff4330739a0559394c19a3dfc8"
                }
              ]
            },
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "99673934a89febe664e704550216638dcb2336a8"
                },
                {
                  "fixed": "87573883c30f1a8555ff720836bb6ea231058539"
                }
              ]
            },
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "978d4fe59665c13db692ba96839f9c52d69f13f3"
                },
                {
                  "fixed": "fb61ffb3fb30a161eb5404c27fc7635e275beafd"
                }
              ]
            },
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "b3d99f43c72b56cf7a104a364e7fb34b0702828b"
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                {
                  "fixed": "1319ea57529e131822bab56bf417c8edc2db9ae8"
                }
              ]
            }
          ],
          "versions": [
            "v6.12.80",
            "v6.12.79",
            "v6.12.78",
            "v6.18.21",
            "v6.18.20",
            "v6.18.19",
            "v6.18.18",
            "v6.18.17",
            "v6.19.11",
            "v6.19.10",
            "v6.19.9",
            "v6.19.8",
            "v6.19.7"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43323.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.12.78"
                },
                {
                  "fixed": "6.12.81"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.18.17"
                },
                {
                  "fixed": "6.18.22"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.7"
                },
                {
                  "fixed": "6.19.12"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43323.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:52.385020837Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/1319ea57529e131822bab56bf417c8edc2db9ae8",
        "https://git.kernel.org/stable/c/87573883c30f1a8555ff720836bb6ea231058539",
        "https://git.kernel.org/stable/c/c089147074ed96ff4330739a0559394c19a3dfc8",
        "https://git.kernel.org/stable/c/fb61ffb3fb30a161eb5404c27fc7635e275beafd",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43323.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-43323",
        "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/2026/43xxx/CVE-2026-43323.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-43323",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 521041,
  "published_at": "2026-05-08T13:31:08.188+00:00"
}