ipv6: Fix soft lockups in fib6_select_path under high next hop churn

{
  "id": "6f750ac7840c5c7322591a1b32eef9617b245ab12f79f74ccc88027ed22ea052",
  "url": "https://osv.dev/vulnerability/CVE-2024-56703",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ipv6: Fix soft lockups in fib6_select_path under high next hop churn",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ipv6: Fix soft lockups in fib6_select_path under high next hop churn Soft lockups have been observed on a cluster of Linux-based edge routers located in a highly dynamic environment. Using the `bird` service, these routers continuously update BGP-advertised routes due to frequently changing nexthop destinations, while also managing significant IPv6 traffic. The lockups occur during the traversal of the multipath circular linked-list in the `fib6_select_path` function, particularly while iterating through the siblings in the list. The issue typically arises when the nodes of the linked list are unexpectedly deleted concurrently on a different core—indicated by their 'next' and 'previous' elements pointing back to the node itself and their reference count dropping to zero. This results in an infinite loop, leading to a soft lockup that triggers a system panic via the watchdog timer. Apply RCU primitives in the problematic code sections to resolve the issue. Where necessary, update the references to fib6_siblings to annotate or use the RCU APIs. Include a test script that reproduces the issue. The script periodically updates the routing table while generating a heavy load of outgoing IPv6 traffic through multiple iperf3 clients. It consistently induces infinite soft lockups within a couple of minutes. Kernel log: 0 [ffffbd13003e8d30] machine_kexec at ffffffff8ceaf3eb 1 [ffffbd13003e8d90] __crash_kexec at fffffff",
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      "modified": "2026-10-28T02:30:49.386501460Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://git.kernel.org/stable/c/11edcd026012ac18acee0f1514db3ed1b160fc6f",
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        "https://git.kernel.org/stable/c/d9ccb18f83ea2bb654289b6ecf014fd267cc988b",
        "https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/56xxx/CVE-2024-56703.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2024-56703",
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  "source_id": "core-osv",
  "document_id": 517765,
  "published_at": "2024-12-28T09:46:24.978+00:00"
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