futex: Prevent use-after-free during requeue-PI

{
  "id": "84e021687ab2867f97f1baf3db995c6a1b2d95244c42a478ba0f272f8dbf7322",
  "url": "https://osv.dev/vulnerability/CVE-2025-39977",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "futex: Prevent use-after-free during requeue-PI",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: futex: Prevent use-after-free during requeue-PI syzbot managed to trigger the following race: T1 T2 futex_wait_requeue_pi() futex_do_wait() schedule() futex_requeue() futex_proxy_trylock_atomic() futex_requeue_pi_prepare() requeue_pi_wake_futex() futex_requeue_pi_complete() /* preempt */ * timeout/ signal wakes T1 * futex_requeue_pi_wakeup_sync() // Q_REQUEUE_PI_LOCKED futex_hash_put() // back to userland, on stack futex_q is garbage /* back */ wake_up_state(q->task, TASK_NORMAL); In this scenario futex_wait_requeue_pi() is able to leave without using futex_q::lock_ptr for synchronization. This can be prevented by reading futex_q::task before updating the futex_q::requeue_state. A reference on the task_struct is not needed because requeue_pi_wake_futex() is invoked with a spinlock_t held which implies a RCU read section. Even if T1 terminates immediately after, the task_struct will remain valid during T2's wake_up_state(). A READ_ONCE on futex_q::task before futex_requeue_pi_complete() is enough because it ensures that the variable is read before the state is updated. Read futex_q::task before updating the requeue state, use it for the following wakeup.",
    "evidence": "osv:CVE-2025-39977",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.155",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.109",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.50",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.16.10",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-39977",
      "aliases": [
        "CVE-2025-39977"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "07d91ef510fb16a2e0ca7453222105835b7ba3b8"
                },
                {
                  "fixed": "cb5d19a61274b51b49601214a87af573b43d60fa"
                },
                {
                  "fixed": "348736955ed6ca6e99ca24b93b1d3fbfe352c181"
                },
                {
                  "fixed": "a170b9c0dde83312b8b58ccc91509c7c15711641"
                },
                {
                  "fixed": "d824b2dbdcfe3c390278dd9652ea526168ef6850"
                },
                {
                  "fixed": "b549113738e8c751b613118032a724b772aa83f2"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39977.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.15.0"
                },
                {
                  "fixed": "6.1.155"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.109"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.50"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.16.10"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39977.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:36.903235038Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-082556.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://git.kernel.org/stable/c/348736955ed6ca6e99ca24b93b1d3fbfe352c181",
        "https://git.kernel.org/stable/c/a170b9c0dde83312b8b58ccc91509c7c15711641",
        "https://git.kernel.org/stable/c/b549113738e8c751b613118032a724b772aa83f2",
        "https://git.kernel.org/stable/c/cb5d19a61274b51b49601214a87af573b43d60fa",
        "https://git.kernel.org/stable/c/d824b2dbdcfe3c390278dd9652ea526168ef6850",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39977.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-39977",
        "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/2025/39xxx/CVE-2025-39977.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-39977",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 504371,
  "published_at": "2025-10-15T07:55:58.283+00:00"
}