sched_ext: Fix is_bpf_migration_disabled() false negative on non-PREEMPT_RCU

{
  "id": "a1f2ecb83adf4c13ef9832513b5a37c610920101d746fab63d3ceb4f92d87065",
  "url": "https://osv.dev/vulnerability/CVE-2026-31734",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "sched_ext: Fix is_bpf_migration_disabled() false negative on non-PREEMPT_RCU",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix is_bpf_migration_disabled() false negative on non-PREEMPT_RCU Since commit 8e4f0b1ebcf2 (\"bpf: use rcu_read_lock_dont_migrate() for trampoline.c\"), the BPF prolog (__bpf_prog_enter) calls migrate_disable() only when CONFIG_PREEMPT_RCU is enabled, via rcu_read_lock_dont_migrate(). Without CONFIG_PREEMPT_RCU, the prolog never touches migration_disabled, so migration_disabled == 1 always means the task is truly migration-disabled regardless of whether it is the current task. The old unconditional p == current check was a false negative in this case, potentially allowing a migration-disabled task to be dispatched to a remote CPU and triggering scx_error in task_can_run_on_remote_rq(). Only apply the p == current disambiguation when CONFIG_PREEMPT_RCU is enabled, where the ambiguity with the BPF prolog still exists.",
    "evidence": "osv:CVE-2026-31734",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.22",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.12",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-31734",
      "aliases": [
        "CVE-2026-31734"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "8e4f0b1ebcf2180ab594f204f01279a666dadf3b"
                },
                {
                  "fixed": "72c43eb2e334febe93018cfb68ae828f55c6e49e"
                },
                {
                  "fixed": "b4992a9446bb9a639007bfd32bf5c5a7e30199e5"
                },
                {
                  "fixed": "0c4a59df370bea245695c00aaae6ae75747139bd"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31734.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.18.0"
                },
                {
                  "fixed": "6.18.22"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "6.19.12"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31734.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:43.806246478Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0c4a59df370bea245695c00aaae6ae75747139bd",
        "https://git.kernel.org/stable/c/72c43eb2e334febe93018cfb68ae828f55c6e49e",
        "https://git.kernel.org/stable/c/b4992a9446bb9a639007bfd32bf5c5a7e30199e5",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31734.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31734",
        "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-2026-31734.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-31734",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 511684,
  "published_at": "2026-05-01T14:14:32.217+00:00"
}