ipv6: null-check fib6_node before accessing in __ip6_del_rt_siblings()

{
  "id": "b2f71d5a129a908d5d6adfe1abd89fb4004addf0a7872c8ede6901903ec3b763",
  "url": "https://osv.dev/vulnerability/CVE-2026-97974",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ipv6: null-check fib6_node before accessing in __ip6_del_rt_siblings()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ipv6: null-check fib6_node before accessing in __ip6_del_rt_siblings() syzbot reported a null-ptr-deref in __ip6_del_rt_siblings() [0]. The stack trace hinted towards a null dereference of rt->fib6_node when fn->leaf is accessed in __ip6_del_rt_siblings(). With RTNL_FLAG_DOIT_UNLOCKED set, inet6_rtm_delroute() operations run concurrently without acquiring the RTNL lock. In ip6_route_del(), the route lookup happens under rcu_read_lock() without acquiring table->tb6_lock. Between ip6_route_del() looking up the route and __ip6_del_rt_siblings() acquiring table->tb6_lock, another thread can modify the routing table. For example, when an ECMP route is replaced via RTM_NEWROUTE with NLM_F_REPLACE, fib6_add_rt2node() unlinks all old siblings and sets iter->fib6_node = NULL. A reproducer was found that triggers this [1]. Add a check to ensure rt->fib6_node is non-null before accessing it. [0] KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027] RIP: 0010:__ip6_del_rt_siblings+0x31e/0x7c0 net/ipv6/route.c:4056 Call Trace: ip6_route_del+0x1054/0x1110 net/ipv6/route.c:4232 inet6_rtm_delroute+0x5d7/0x6d0 net/ipv6/route.c:5669 rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7132 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline] netlink_unicast+0x7f5/0x990 net/netlink/af_netlink.c:1345 netlink_sendmsg+0x813/0xb40 net/netlink/af_netli",
    "evidence": "osv:CVE-2026-97974",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.53",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.2.7",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-97974",
      "aliases": [
        "CVE-2026-97974"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "bd11ff421d36abdb585b9104fa70057bf01b3110"
                },
                {
                  "fixed": "e7ff91f19c1aae039a4257fa86fe849afe185291"
                },
                {
                  "fixed": "1155234c2227cf36072a43e1e09119472ade7ca7"
                },
                {
                  "fixed": "cdca92eddc025fdb90071be97738f7d55a65f8dd"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97974.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.16.0"
                },
                {
                  "fixed": "6.18.53"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.2.7"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97974.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:22.874199337Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/1155234c2227cf36072a43e1e09119472ade7ca7",
        "https://git.kernel.org/stable/c/cdca92eddc025fdb90071be97738f7d55a65f8dd",
        "https://git.kernel.org/stable/c/e7ff91f19c1aae039a4257fa86fe849afe185291",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97974.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-97974",
        "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/2026/97xxx/CVE-2026-97974.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-97974",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 489294,
  "published_at": "2026-09-25T10:23:13.373+00:00"
}