ipv6: fix a BUG in rt6_get_pcpu_route() under PREEMPT_RT

{
  "id": "3834e466e57d23af1fddf269deff26c02cb8df6fc0cf716cdf4ba8ac20767b88",
  "url": "https://osv.dev/vulnerability/CVE-2025-71080",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ipv6: fix a BUG in rt6_get_pcpu_route() under PREEMPT_RT",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ipv6: fix a BUG in rt6_get_pcpu_route() under PREEMPT_RT On PREEMPT_RT kernels, after rt6_get_pcpu_route() returns NULL, the current task can be preempted. Another task running on the same CPU may then execute rt6_make_pcpu_route() and successfully install a pcpu_rt entry. When the first task resumes execution, its cmpxchg() in rt6_make_pcpu_route() will fail because rt6i_pcpu is no longer NULL, triggering the BUG_ON(prev). It's easy to reproduce it by adding mdelay() after rt6_get_pcpu_route(). Using preempt_disable/enable is not appropriate here because ip6_rt_pcpu_alloc() may sleep. Fix this by handling the cmpxchg() failure gracefully on PREEMPT_RT: free our allocation and return the existing pcpu_rt installed by another task. The BUG_ON is replaced by WARN_ON_ONCE for non-PREEMPT_RT kernels where such races should not occur.",
    "evidence": "osv:CVE-2025-71080",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.64",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.4",
            "evidence": "/affected/1/ranges"
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    "severity": "high",
    "structured": {
      "id": "CVE-2025-71080",
      "aliases": [
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      "metrics": [
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          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
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              "type": "ECOSYSTEM",
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                  "introduced": "6.12.0"
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                  "fixed": "6.12.64"
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              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.13.0"
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            "ecosystem": "Linux"
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      "modified": "2026-10-28T02:30:28.753904013Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/1adaea51c61b52e24e7ab38f7d3eba023b2d050d",
        "https://git.kernel.org/stable/c/1dc33ad0867325f8d2c6d7b2a6f542d4f3121f66",
        "https://git.kernel.org/stable/c/787515ccb2292f82eb0876993129154629a49651",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/71xxx/CVE-2025-71080.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-71080",
        "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/2025/71xxx/CVE-2025-71080.json"
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    "severity_evidence": "/severity/0/score"
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  "source_id": "core-osv",
  "document_id": 495045,
  "published_at": "2026-01-13T15:34:44.832+00:00"
}