perf/core: Fix refcount bug and potential UAF in perf_mmap

{
  "id": "b420bd8c7f9c816d7b3564c011dc14916e79675606ce10d4a46015a1f81fea39",
  "url": "https://osv.dev/vulnerability/CVE-2026-23248",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "perf/core: Fix refcount bug and potential UAF in perf_mmap",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: perf/core: Fix refcount bug and potential UAF in perf_mmap Syzkaller reported a refcount_t: addition on 0; use-after-free warning in perf_mmap. The issue is caused by a race condition between a failing mmap() setup and a concurrent mmap() on a dependent event (e.g., using output redirection). In perf_mmap(), the ring_buffer (rb) is allocated and assigned to event->rb with the mmap_mutex held. The mutex is then released to perform map_range(). If map_range() fails, perf_mmap_close() is called to clean up. However, since the mutex was dropped, another thread attaching to this event (via inherited events or output redirection) can acquire the mutex, observe the valid event->rb pointer, and attempt to increment its reference count. If the cleanup path has already dropped the reference count to zero, this results in a use-after-free or refcount saturation warning. Fix this by extending the scope of mmap_mutex to cover the map_range() call. This ensures that the ring buffer initialization and mapping (or cleanup on failure) happens atomically effectively, preventing other threads from accessing a half-initialized or dying ring buffer.",
    "evidence": "osv:CVE-2026-23248",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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            "value": "6.18.17",
            "evidence": "/affected/1/ranges"
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            "value": "6.19.7",
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      "modified": "2026-10-28T02:30:52.442090812Z",
      "provider": "osv",
      "references": [
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        "https://git.kernel.org/stable/c/ac7ecb65af170a7fc193e7bd8be15dac84ec6a56",
        "https://git.kernel.org/stable/c/c27dea9f50ed525facb62ef647dddc4722456e07",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23248.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-23248",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
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  "source_id": "core-osv",
  "document_id": 521385,
  "published_at": "2026-03-18T10:05:10.07+00:00"
}