posix-cpu-timers: Use u64 multiplication in update_rlimit_cpu()

{
  "id": "99b55644334274a2c8b95b3eb7ed9a7698a8c79f397aa2639352b620683920e5",
  "url": "https://osv.dev/vulnerability/CVE-2026-72068",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "posix-cpu-timers: Use u64 multiplication in update_rlimit_cpu()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: posix-cpu-timers: Use u64 multiplication in update_rlimit_cpu() update_rlimit_cpu() converts the RLIMIT_CPU value to nanoseconds with u64 nsecs = rlim_new * NSEC_PER_SEC; On 32-bit kernels both rlim_new (unsigned long) and NSEC_PER_SEC (1000000000L) are 32-bit, so the multiplication is performed in unsigned long and truncated for rlim_new > 4 seconds before being widened to u64. The same file already casts to u64 for the matching computation in check_process_timers(): u64 softns = (u64)soft * NSEC_PER_SEC; As a result, the truncated value is installed into the CPUCLOCK_PROF expiry cache (nextevt), causing the process CPU timer to be programmed to fire prematurely for any RLIMIT_CPU soft limit >= 5 seconds. The actual SIGXCPU/SIGKILL decision in check_process_timers() already casts to u64 and is therefore correct, so limit enforcement is not broken; only the expiry-cache programming is wrong. Apply the same cast here so both paths convert rlim_cur identically. 64-bit kernels are unaffected.",
    "evidence": "osv:CVE-2026-72068",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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            "value": "5.10.261",
            "evidence": "/affected/1/ranges"
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          {
            "value": "7.1.5",
            "evidence": "/affected/1/ranges"
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        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-72068",
      "aliases": [
        "CVE-2026-72068"
      ],
      "affected": [
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                  "fixed": "384628d6cdde0fcd76868606fad3ad8293100afb"
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                  "fixed": "1fafc4d9b411645eb34de43362b966dc8fb3e263"
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
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      ],
      "modified": "2026-10-28T02:30:29.007848346Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/1fafc4d9b411645eb34de43362b966dc8fb3e263",
        "https://git.kernel.org/stable/c/26aff38fefb1d6cd87e22525f41cc8f1aa61b24f",
        "https://git.kernel.org/stable/c/384628d6cdde0fcd76868606fad3ad8293100afb",
        "https://git.kernel.org/stable/c/571e1f10b5996ba3e4dc63ea77de4aa309c384ce",
        "https://git.kernel.org/stable/c/cff8281bacd2866767e6194c3079d33b6c5a74f4",
        "https://git.kernel.org/stable/c/ea6a188ee805e841a0e242f14d15953e0dfa74bb",
        "https://git.kernel.org/stable/c/edf6babb9edd2d3e19229ade339081f439d4f478",
        "https://git.kernel.org/stable/c/feb5c87c8514444ba891b75a5a3eae57c64edaf8",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72068.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-72068",
        "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-2026-72068.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-72068",
        "evidence": "/id"
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    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 495911,
  "published_at": "2026-08-15T05:52:21.007+00:00"
}