sched_ext: Build the cid tables privately and publish them with RCU

{
  "id": "b121ceef0a6128203404f667ca2288b97eb20ca5f01bf8272cfe9f1154fc37a4",
  "url": "https://osv.dev/vulnerability/CVE-2026-98942",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "sched_ext: Build the cid tables privately and publish them with RCU",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: sched_ext: Build the cid tables privately and publish them with RCU The cid tables are visible to the cid kfuncs while being modified: the first enable publishes the global pointers before filling them, ops.init_cids() overrides rewrite them in place, and re-enables rebuild them in place. A racing TRACING or SYSCALL program can read unfilled entries, including uninitialized memory in the kmalloc'd tables, or torn topo updates. Tie the tables' lifetimes to the root sched instead: each root enable builds a fresh set privately and publishes the per-table __rcu globals once the layout is final, and root disable unpublishes and RCU-frees the set. A non-NULL global is now always a fully built table which stays valid for the reader's RCU read section, and lookups stay two loads. Kfuncs treat NULL as no-mapping, also after the scheduler exits instead of reporting the stale last mapping. The cid kfuncs are available whether the root scheduler is cid-form or cpu-form, the latter to allow gradual migration to cids. Every root therefore builds and publishes a default mapping. Every reader must either be gated on scheduler liveness or NULL-check inside an RCU read section. Fix the two kfuncs that were neither: scx_bpf_this_cid() read the table with no RCU or preemption protection and scx_bpf_task_cid() relied on KF_RCU, which doesn't put a sleepable program in an RCU read section. The hotplug callbacks are instead seriali",
    "evidence": "osv:CVE-2026-98942",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.10",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-98942",
      "aliases": [
        "CVE-2026-98942"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e9b55af47edf6e60c9a47b5604c3e15c5162ec86"
                },
                {
                  "fixed": "0e1a74369bdbc357d3d9713734418d914a981553"
                },
                {
                  "fixed": "3a773220d39ba993dfe5d135f8b610be10794d5d"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98942.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "7.2.0"
                },
                {
                  "fixed": "7.2.10"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98942.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:45.598633931Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0e1a74369bdbc357d3d9713734418d914a981553",
        "https://git.kernel.org/stable/c/3a773220d39ba993dfe5d135f8b610be10794d5d",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98942.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98942",
        "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/2026/98xxx/CVE-2026-98942.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-98942",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 513820,
  "published_at": "2026-10-23T12:12:14.18+00:00"
}