{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-89791",
  "modified": "2026-10-07T14:35:31Z",
  "upstream": [
    "CVE-2026-89791"
  ],
  "published": "2026-09-16T08:46:47Z",
  "summary": "perf: Fix use-after-free when perf mmap() revival races with the last munmap()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nperf: Fix use-after-free when perf mmap() revival races with the last munmap()\n\nperf_mmap_close() drops rb->mmap_count *without* holding\nevent->mmap_mutex (the refcount_dec_and_test() right before the\nrefcount_dec_and_mutex_lock() of event->mmap_count). A concurrent\nperf_mmap_rb() can slot its entire \"revival\" path into that window\n(perf_mmap holds event->mmap_mutex for its whole duration, including\nrb_alloc):\n\n  munmap side (perf_mmap_close)          mmap side (perf_mmap_rb)\n  -----------------------------------    --------------------------------\n  rb->mmap_count 1 -> 0   (no lock)      (holds event->mmap_mutex)\n                                         inc_not_zero(rb->mmap_count) fails\n                                         ring_buffer_attach(event, NULL)\n                                         rb_alloc() + attach new rb\n                                         refcount_set(&event->mmap_count, 1)\n  lock; event->mmap_count 1 -> 0\n  ring_buffer_attach(event, NULL)\n  ring_buffer_put() -> frees the *new* rb\n\nThe revival's refcount_set(&event->mmap_count, 1) is an invisible\n1 -> 1 write: the close frees the just-revived buffer although the\nother process still has it mapped -- a page-level use-after-free\nallowing local privilege escalation to root by any unprivileged user\n(default kernel.perf_event_paranoid=2).\n\nSwap the order of the two counter updates: event->mmap_count is\ndropped first via refcount_dec_and_mutex_lock(), so its 1 -> 0\ntransition and the ring_buffer_attach() stay serialized with\nperf_mmap(). rb->mmap_count == 0 then implies every event using the\nbuffer is detached already, so the result of the rb->mmap_count drop\ncan gate the remaining teardown directly and detach_rest is no longer\nneeded.\n\nAn earlier fix for this race from Kyle Zeng and David Lee takes\nevent->mmap_mutex around both counter updates [0]; here the not-last\nclose stays lockless.",
  "affected": [
    {
      "package": {
        "ecosystem": "Raspberry Pi OS:13",
        "name": "linux"
      },
      "versions": [
        "1:6.18.29-1+rpt1",
        "1:6.18.33-1+rpt1",
        "1:6.18.34-1+rpt1",
        "1:6.18.39-1+rpt1",
        "1:6.18.50-1+rpt1"
      ],
      "ecosystem_specific": {
        "binaries": [
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            "binary_version": "1:6.18.29-1+rpt1"
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            "binary_version": "1:6.18.29-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.18.29+rpt-rpi-v7",
            "binary_version": "1:6.18.29-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.18.29+rpt-rpi-v8",
            "binary_version": "1:6.18.29-1+rpt1"
          },
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            "binary_version": "1:6.18.29-1+rpt1"
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            "binary_name": "linux-image-6.18.33+rpt-rpi-2712",
            "binary_version": "1:6.18.33-1+rpt1"
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            "binary_version": "1:6.18.33-1+rpt1"
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            "binary_version": "1:6.18.34-1+rpt1"
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            "binary_name": "linux-image-6.18.34+rpt-rpi-v8-rt",
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            "binary_version": "1:6.18.39-1+rpt1"
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          },
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      "database_specific": {
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            "linux_commit": "66318c5b5cd8145a662303af12ed39ac07eb27cc",
            "upstream_version": "6.18.29",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.18.52"
          },
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            "linux_commit": "95b85bebbedcaedfa7ca79116ed38b7376fba412",
            "upstream_version": "6.18.33",
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  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-89791"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/929cb3b9dc818dd9fa89d510d4ff2b255e42badd"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/0c739f54f1c77f3a4643160cd2e031b6c2f2aab6"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/58a8108bc73de0740d5b88150465d6690ea5f85f"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-09-16T14:40:32Z"
  }
}