cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()

{
  "id": "aaf7db559b8fac199cbbb8d00498e7e8ce7172bf3951222bc9a804b489fb2e1a",
  "url": "https://osv.dev/vulnerability/CVE-2026-72016",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable() On arm64, when booting with `maxcpus` greater than the number of present CPUs (e.g., QEMU -smp cpus=4,maxcpus=8), some CPUs are marked as 'present' but have not yet been registered via register_cpu(). Consequently, the per-cpu device objects for these CPUs are not yet initialized. In cpuhp_smt_enable(), the code iterates over all present CPUs. Calling _cpu_up() for these unregistered CPUs eventually leads to sysfs_create_group() being called with a NULL kobject (or a kobject without a directory), triggering the following warning in fs/sysfs/group.c: WARNING: fs/sysfs/group.c:137 at internal_create_group+0x41c/0x4bc, CPU#2: sh/181 [...] Call trace: internal_create_group+0x41c/0x4bc (P) sysfs_create_group+0x18/0x24 topology_add_dev+0x1c/0x28 cpuhp_invoke_callback+0x104/0x20c __cpuhp_invoke_callback_range+0x94/0x11c _cpu_up+0x200/0x37c When booting with ACPI, arm64 smp_prepare_cpus() currently sets all enumerated CPUs as \"present\" regardless of their status in the MADT. This causes issues with SMT hotplug control. For instance, with QEMU's \"-smp 4,maxcpus=8\" configuration, the MADT GICC entries are populated as follows: 1. The first four CPUs: `Enabled` set but `Online Capable` not set. 2. The remaining four CPUs: `Online Capable` set but `Enabled` not set to support potential hot-plugging. Fix this by: 1. When booting with ACPI, checking the ACPI_MADT_",
    "evidence": "osv:CVE-2026-72016",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.40",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.1.5",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-72016",
      "aliases": [
        "CVE-2026-72016"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb"
                },
                {
                  "fixed": "ccdf1770a4ba27e31599d24ad970d77a371c7912"
                },
                {
                  "fixed": "901a489d89ee9c854624c8444090e38e70aed234"
                },
                {
                  "fixed": "f9a82544c7174851f5c7524622f5966dcafd3a47"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-72016.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.15.0"
                },
                {
                  "fixed": "6.18.40"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.1.5"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-72016.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:21.226326308Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/901a489d89ee9c854624c8444090e38e70aed234",
        "https://git.kernel.org/stable/c/ccdf1770a4ba27e31599d24ad970d77a371c7912",
        "https://git.kernel.org/stable/c/f9a82544c7174851f5c7524622f5966dcafd3a47",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72016.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-72016",
        "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/2026/72xxx/CVE-2026-72016.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-72016",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 487403,
  "published_at": "2026-08-15T05:51:44.05+00:00"
}