net/sched: cls_api: fix error handling causing NULL dereference

{
  "id": "2eed8554735b44471607cd34e70c3634486e67ac5ef8027bba3705119058a0b5",
  "url": "https://osv.dev/vulnerability/CVE-2025-21857",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net/sched: cls_api: fix error handling causing NULL dereference",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_api: fix error handling causing NULL dereference tcf_exts_miss_cookie_base_alloc() calls xa_alloc_cyclic() which can return 1 if the allocation succeeded after wrapping. This was treated as an error, with value 1 returned to caller tcf_exts_init_ex() which sets exts->actions to NULL and returns 1 to caller fl_change(). fl_change() treats err == 1 as success, calling tcf_exts_validate_ex() which calls tcf_action_init() with exts->actions as argument, where it is dereferenced. Example trace: BUG: kernel NULL pointer dereference, address: 0000000000000000 CPU: 114 PID: 16151 Comm: handler114 Kdump: loaded Not tainted 5.14.0-503.16.1.el9_5.x86_64 #1 RIP: 0010:tcf_action_init+0x1f8/0x2c0 Call Trace: tcf_action_init+0x1f8/0x2c0 tcf_exts_validate_ex+0x175/0x190 fl_change+0x537/0x1120 [cls_flower]",
    "evidence": "osv:CVE-2025-21857",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.6.80",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.17",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.13.5",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "CVE-2025-21857",
      "aliases": [
        "CVE-2025-21857"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "3e4c56cf41876ef2a82f0877fe2a67648f8632b8"
                },
                {
                  "fixed": "3c74b5787caf59bb1e9c5fe0a360643a71eb1e8a"
                },
                {
                  "fixed": "071ed42cff4fcdd89025d966d48eabef59913bf2"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21857.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.3.0"
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                {
                  "fixed": "6.6.80"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
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                {
                  "fixed": "6.12.17"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.13.5"
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              ]
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21857.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:52.634289989Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/071ed42cff4fcdd89025d966d48eabef59913bf2",
        "https://git.kernel.org/stable/c/3c74b5787caf59bb1e9c5fe0a360643a71eb1e8a",
        "https://git.kernel.org/stable/c/3e4c56cf41876ef2a82f0877fe2a67648f8632b8",
        "https://git.kernel.org/stable/c/de4b679aa3b4da7ec34f639df068b914f20e3c3c",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21857.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-21857",
        "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/2025/21xxx/CVE-2025-21857.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-21857",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 521082,
  "published_at": "2025-03-12T09:42:10.622+00:00"
}