sched/core: Fix use-after-free bug in dup_user_cpus_ptr()

{
  "id": "a696e319e45996a9705a0a51353ea54f90534e9c2a018575dcee304d22fbd760",
  "url": "https://osv.dev/vulnerability/CVE-2022-48892",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "sched/core: Fix use-after-free bug in dup_user_cpus_ptr()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: sched/core: Fix use-after-free bug in dup_user_cpus_ptr() Since commit 07ec77a1d4e8 (\"sched: Allow task CPU affinity to be restricted on asymmetric systems\"), the setting and clearing of user_cpus_ptr are done under pi_lock for arm64 architecture. However, dup_user_cpus_ptr() accesses user_cpus_ptr without any lock protection. Since sched_setaffinity() can be invoked from another process, the process being modified may be undergoing fork() at the same time. When racing with the clearing of user_cpus_ptr in __set_cpus_allowed_ptr_locked(), it can lead to user-after-free and possibly double-free in arm64 kernel. Commit 8f9ea86fdf99 (\"sched: Always preserve the user requested cpumask\") fixes this problem as user_cpus_ptr, once set, will never be cleared in a task's lifetime. However, this bug was re-introduced in commit 851a723e45d1 (\"sched: Always clear user_cpus_ptr in do_set_cpus_allowed()\") which allows the clearing of user_cpus_ptr in do_set_cpus_allowed(). This time, it will affect all arches. Fix this bug by always clearing the user_cpus_ptr of the newly cloned/forked task before the copying process starts and check the user_cpus_ptr state of the source task under pi_lock. Note to stable, this patch won't be applicable to stable releases. Just copy the new dup_user_cpus_ptr() function over.",
    "evidence": "osv:CVE-2022-48892",
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      "modified": "2026-10-28T02:30:20.458381470Z",
      "provider": "osv",
      "references": [
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        "https://git.kernel.org/stable/c/87ca4f9efbd7cc649ff43b87970888f2812945b8",
        "https://git.kernel.org/stable/c/b22faa21b6230d5eccd233e1b7e0026a5002b287",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2022/48xxx/CVE-2022-48892.json",
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  "source_id": "core-osv",
  "document_id": 486501,
  "published_at": "2024-08-21T06:10:24.407+00:00"
}