bpf: Reject key-less BTF for hash maps

{
  "id": "cbaf05991f137850dc4204c6ba0affa9aa70fa91a095b1f151138d9c774ed802",
  "url": "https://osv.dev/vulnerability/CVE-2026-98065",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "bpf: Reject key-less BTF for hash maps",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: bpf: Reject key-less BTF for hash maps map_check_btf() allows a key-less BTF (btf_key_type_id == 0) only for maps that have a ->map_check_btf callback, and leaves the actual decision to that callback. Hash maps used to have no ->map_check_btf, so a key-less BTF was rejected outright. That changed when htab and rhtab gained a ->map_check_btf to register a dtor - htab in commit 1df97a7453ee (\"bpf: Register dtor for freeing special fields\") and rhtab in commit 6905f8601298 (\"bpf: Allow special fields in resizable hashtab\"). Neither looks at the key, so a key-less hash map now passes map_check_btf() and gets created. Reading it back through bpffs feeds the key type_id 0 into btf_type_seq_show(); btf_type_by_id() returns the void type, kind_ops[BTF_KIND_UNKN] is NULL, and btf_type_show() dereferences it: RIP: 0010:btf_type_show+0x223/0x2e0 kernel/bpf/btf.c:8232 RSP: 0018:ffffc9000399f868 EFLAGS: 00010206 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000028 RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 R10: ffffc9000399f970 R11: 0000000000000001 R12: ffffffff9b96b140 R13: ffffc9000399f8e0 R14: ffff88803d393c00 R15: 0000000000000003 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000000000 CR3: 000000003d213000 CR4: 0000000000352ef0 DR0: 0000000039ae8f55 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 000",
    "evidence": "osv:CVE-2026-98065",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.7",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-98065",
      "aliases": [
        "CVE-2026-98065"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "451a84a3ad3c897c03181af433e7c98640730f1f"
                },
                {
                  "fixed": "54098e3fe34ec190bc256b338b9a93c7e2dc9354"
                }
              ]
            },
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "51a17f0ce19c4ee2a25cf16c93490d509b1ebb0a"
                },
                {
                  "fixed": "fa047f2a025003f5654ebd76539f16a6ead0401a"
                }
              ]
            },
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "1df97a7453eec80c1912c2d0360290a3970a7671"
                },
                {
                  "fixed": "7ca231252820c47aaec42a5db580db98f9b64724"
                },
                {
                  "fixed": "0895a0c0734703be5532f3883c42db95615fd98b"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98065.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "7.0.0"
                },
                {
                  "fixed": "7.2.7"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98065.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:40.926754641Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0895a0c0734703be5532f3883c42db95615fd98b",
        "https://git.kernel.org/stable/c/54098e3fe34ec190bc256b338b9a93c7e2dc9354",
        "https://git.kernel.org/stable/c/7ca231252820c47aaec42a5db580db98f9b64724",
        "https://git.kernel.org/stable/c/fa047f2a025003f5654ebd76539f16a6ead0401a",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98065.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98065",
        "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/2026/98xxx/CVE-2026-98065.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-98065",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 508715,
  "published_at": "2026-09-25T10:24:08.406+00:00"
}