CVE-2026-72016 (GCVE-0-2026-72016)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:51 – Updated: 2026-08-17 05:06
VLAI
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_ENABLED flag in the GICC entry before calling set_cpu_present() during SMP initialization. 2. Properly managing the present mask in acpi_map_cpu() and acpi_unmap_cpu() to support actual CPU hotplug events, This aligns with other architectures like x86 and LoongArch. 3. Update the arm64 CPU hotplug documentation to no longer state that all online-capable vCPUs are marked as present by the kernel at boot time. This ensures that only physically available or explicitly enabled CPUs are in the present mask, keeping the SMT control logic consistent with the actual hardware state.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb , < ccdf1770a4ba27e31599d24ad970d77a371c7912 (git)
Affected: eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb , < 901a489d89ee9c854624c8444090e38e70aed234 (git)
Affected: eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb , < f9a82544c7174851f5c7524622f5966dcafd3a47 (git)
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Linux Linux Affected: 6.15
Unaffected: 0 , < 6.15 (semver)
Unaffected: 6.18.40 , ≤ 6.18.* (semver)
Unaffected: 7.1.5 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
            "Documentation/arch/arm64/cpu-hotplug.rst",
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          "vendor": "Linux",
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              "operator": "OR"
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        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ncpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()\n\nOn arm64, when booting with `maxcpus` greater than the number of present\nCPUs (e.g., QEMU -smp cpus=4,maxcpus=8), some CPUs are marked as \u0027present\u0027\nbut have not yet been registered via register_cpu(). Consequently,\nthe per-cpu device objects for these CPUs are not yet initialized.\n\nIn cpuhp_smt_enable(), the code iterates over all present CPUs. Calling\n_cpu_up() for these unregistered CPUs eventually leads to\nsysfs_create_group() being called with a NULL kobject (or a kobject\nwithout a directory), triggering the following warning in\nfs/sysfs/group.c:\n\n  WARNING: fs/sysfs/group.c:137 at internal_create_group+0x41c/0x4bc, CPU#2: sh/181\n  [...]\n  Call trace:\n    internal_create_group+0x41c/0x4bc (P)\n    sysfs_create_group+0x18/0x24\n    topology_add_dev+0x1c/0x28\n    cpuhp_invoke_callback+0x104/0x20c\n    __cpuhp_invoke_callback_range+0x94/0x11c\n    _cpu_up+0x200/0x37c\n\nWhen booting with ACPI, arm64 smp_prepare_cpus() currently sets all\nenumerated CPUs as \"present\" regardless of their status in the MADT. This\ncauses issues with SMT hotplug control. For instance, with QEMU\u0027s\n\"-smp 4,maxcpus=8\" configuration, the MADT GICC entries are populated as\nfollows:\n\n1. The first four CPUs: `Enabled` set but `Online Capable` not set.\n\n2. The remaining four CPUs: `Online Capable` set but `Enabled` not set\n   to support potential hot-plugging.\n\nFix this by:\n\n1. When booting with ACPI, checking the ACPI_MADT_ENABLED flag in the GICC\n   entry before calling set_cpu_present() during SMP initialization.\n\n2. Properly managing the present mask in acpi_map_cpu() and\n   acpi_unmap_cpu() to support actual CPU hotplug events, This aligns with\n   other architectures like x86 and LoongArch.\n\n3. Update the arm64 CPU hotplug documentation to no longer state that all\n   online-capable vCPUs are marked as present by the kernel at boot time.\n\nThis ensures that only physically available or explicitly enabled CPUs\nare in the present mask, keeping the SMT control logic consistent with\nthe actual hardware state."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:06:38.684Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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        {
          "url": "https://git.kernel.org/stable/c/ccdf1770a4ba27e31599d24ad970d77a371c7912"
        },
        {
          "url": "https://git.kernel.org/stable/c/901a489d89ee9c854624c8444090e38e70aed234"
        },
        {
          "url": "https://git.kernel.org/stable/c/f9a82544c7174851f5c7524622f5966dcafd3a47"
        }
      ],
      "title": "cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-72016",
    "datePublished": "2026-08-15T05:51:44.050Z",
    "dateReserved": "2026-08-09T03:40:39.900Z",
    "dateUpdated": "2026-08-17T05:06:38.684Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "cve": "CVE-2026-72016",
      "date": "2026-08-24",
      "epss": "0.00198",
      "percentile": "0.09548"
    },
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-17T16:06:11+00:00",
      "cve": "CVE-2026-72016",
      "id": "CVE-2026-72016",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-72016.json",
      "version": "3"
    }
  }
}



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