net: ethtool: netlink: Allow NULL nlattrs when getting a phy_device

{
  "id": "e67682e3e1d8291690f9522ac05b966dc6788b8d28c390788e5fbb6b5143f971",
  "url": "https://osv.dev/vulnerability/CVE-2025-21921",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net: ethtool: netlink: Allow NULL nlattrs when getting a phy_device",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net: ethtool: netlink: Allow NULL nlattrs when getting a phy_device ethnl_req_get_phydev() is used to lookup a phy_device, in the case an ethtool netlink command targets a specific phydev within a netdev's topology. It takes as a parameter a const struct nlattr *header that's used for error handling : if (!phydev) { NL_SET_ERR_MSG_ATTR(extack, header, \"no phy matching phyindex\"); return ERR_PTR(-ENODEV); } In the notify path after a ->set operation however, there's no request attributes available. The typical callsite for the above function looks like: phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_XXX_HEADER], info->extack); So, when tb is NULL (such as in the ethnl notify path), we have a nice crash. It turns out that there's only the PLCA command that is in that case, as the other phydev-specific commands don't have a notification. This commit fixes the crash by passing the cmd index and the nlattr array separately, allowing NULL-checking it directly inside the helper.",
    "evidence": "osv:CVE-2025-21921",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.19",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.13.7",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2025-21921",
      "aliases": [
        "CVE-2025-21921"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "639c70352958735addbba5ae7dd65985da96e061"
                },
                {
                  "fixed": "1f458fa42c29144cef280e05bc49fc21b873d897"
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                  "fixed": "637399bf7e77797811adf340090b561a8f9d1213"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21921.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.12.0"
                },
                {
                  "fixed": "6.12.19"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.13.7"
                }
              ]
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21921.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:21.363313261Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/1f458fa42c29144cef280e05bc49fc21b873d897",
        "https://git.kernel.org/stable/c/637399bf7e77797811adf340090b561a8f9d1213",
        "https://git.kernel.org/stable/c/639c70352958735addbba5ae7dd65985da96e061",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21921.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-21921",
        "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-2025-21921.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-21921",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 487488,
  "published_at": "2025-04-01T15:40:55.11+00:00"
}