netlink: do not free nlk->groups while lockless readers can use it

{
  "id": "0ad8ae37764216a542affa6dda07e35fad4f30c922d3abd40bd9cdd4d603e5f2",
  "url": "https://osv.dev/vulnerability/CVE-2026-98284",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "netlink: do not free nlk->groups while lockless readers can use it",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: netlink: do not free nlk->groups while lockless readers can use it netlink_realloc_groups() uses krealloc() under netlink_table_grab(). Whenever NLGRPSZ(groups) lands in a different kmalloc bucket, the old bitmap is freed immediately. Two readers of nlk->groups / nlk->ngroups do not hold the netlink table lock: 1) sk_diag_dump_groups(). Hashed (bound) sockets are dumped from the rhashtable walk in __netlink_diag_dump(), which only holds RCU. Only the mc_list part of the dump takes nl_table_lock. 2) netlink_native_seq_show() (/proc/net/netlink), whose walk has been lockless since commit 21e4902aea80 (\"netlink: Lockless lookup with RCU grace period in socket release\"). Both can read a freed buffer, and sk_diag_dump_groups() can also read past the end of the old (smaller) buffer if it happens to load the old @groups pointer together with the new @ngroups value, copying the result into a NETLINK_DIAG_GROUPS attribute. This is the same class of bug that commit f773608026ee (\"netlink: access nlk groups safely in netlink bind and getname\") fixed for bind() and getname(); these two readers were missed. Simply grabbing the table lock in sk_diag_dump_groups() is not an option, because it is also called with nl_table_lock already held from the mc_list section of the dump. Make the lockless readers safe instead: - Allocate a new bitmap and free the old one after an RCU grace period, instead of relying on the implicit kfr",
    "evidence": "osv:CVE-2026-98284",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.8",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-98284",
      "aliases": [
        "CVE-2026-98284"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "21e4902aea80ef35afc00ee8d2abdea4f519b7f7"
                },
                {
                  "fixed": "22f313e211d58a66786c81487c3905fa5d4b2a8f"
                },
                {
                  "fixed": "ceac0de741bfb47ca255eee075257b3bb31f0651"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98284.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "4.0.0"
                },
                {
                  "fixed": "7.2.8"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98284.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:50.760155954Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/22f313e211d58a66786c81487c3905fa5d4b2a8f",
        "https://git.kernel.org/stable/c/ceac0de741bfb47ca255eee075257b3bb31f0651",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98284.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98284",
        "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/2026/98xxx/CVE-2026-98284.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-98284",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 519478,
  "published_at": "2026-10-06T08:45:45.443+00:00"
}