tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req().

{
  "id": "6f1b8f61348efa37222eed222838b9a16557b45aaf20894ede3a758c235e1079",
  "url": "https://osv.dev/vulnerability/CVE-2026-53260",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req().",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req(). syzbot reported a weird reqsk->rsk_refcnt underflow in __inet_csk_reqsk_queue_drop(). The captured reqsk_put() in __inet_csk_reqsk_queue_drop() is called only when it successfully removes reqsk from ehash. Moreover, reqsk_timer_handler() calls another reqsk_put() after that. This indicates that the reqsk was missing both refcnts for ehash and the timer itself. Since all the syzbot reports had PREEMPT_RT enabled, the only possible scenario is that reqsk_queue_hash_req() is preempted after mod_timer() and before refcount_set(), and then the timer triggered after 1s aborts the reqsk due to its listener's close(). Let's wrap mod_timer() and refcount_set() with preempt_disable_nested() and preempt_enable_nested(). Note that inet_ehash_insert() holds the normal spin_lock() (mutex in PREEMPT_RT), so it must be called outside of preempt_disable_nested(), but this is fine. The lookup path just ignores 0 sk_refcnt entries in ehash and tries to create another reqsk, but this will fail at inet_ehash_insert(). [0]: refcount_t: underflow; use-after-free. WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: ktimers/0/16 Modules linked in: CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)} Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Goo",
    "evidence": "osv:CVE-2026-53260",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.97",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.40",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.13",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-53260",
      "aliases": [
        "CVE-2026-53260"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "b183215ff714efb747d9d5a429322ba6404b5401"
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                  "fixed": "e10902df24488ca722303133acfc82490f7d59ad"
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53260.json"
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          "ranges": [
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              "type": "ECOSYSTEM",
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                  "fixed": "6.18.40"
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              "events": [
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53260.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:37.789609135Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/889fc99967007e2493833515a645cb2d800f6742",
        "https://git.kernel.org/stable/c/b183215ff714efb747d9d5a429322ba6404b5401",
        "https://git.kernel.org/stable/c/de5a46f3b2c8d3cd20afa158bd3a725e3e3d6fd3",
        "https://git.kernel.org/stable/c/e10902df24488ca722303133acfc82490f7d59ad",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53260.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-53260",
        "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/2026/53xxx/CVE-2026-53260.json"
      }
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    "related_cves": [
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        "value": "CVE-2026-53260",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 505344,
  "published_at": "2026-06-25T08:39:49.229+00:00"
}