bpf: Enforce expected_attach_type for tailcall compatibility

{
  "id": "bfb7913f60dda3f84b82b26548aa03b5ef4c755af61861df8af73e4b57d4ac09",
  "url": "https://osv.dev/vulnerability/CVE-2025-40123",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "bpf: Enforce expected_attach_type for tailcall compatibility",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: bpf: Enforce expected_attach_type for tailcall compatibility Yinhao et al. recently reported: Our fuzzer tool discovered an uninitialized pointer issue in the bpf_prog_test_run_xdp() function within the Linux kernel's BPF subsystem. This leads to a NULL pointer dereference when a BPF program attempts to deference the txq member of struct xdp_buff object. The test initializes two programs of BPF_PROG_TYPE_XDP: progA acts as the entry point for bpf_prog_test_run_xdp() and its expected_attach_type can neither be of be BPF_XDP_DEVMAP nor BPF_XDP_CPUMAP. progA calls into a slot of a tailcall map it owns. progB's expected_attach_type must be BPF_XDP_DEVMAP to pass xdp_is_valid_access() validation. The program returns struct xdp_md's egress_ifindex, and the latter is only allowed to be accessed under mentioned expected_attach_type. progB is then inserted into the tailcall which progA calls. The underlying issue goes beyond XDP though. Another example are programs of type BPF_PROG_TYPE_CGROUP_SOCK_ADDR. sock_addr_is_valid_access() as well as sock_addr_func_proto() have different logic depending on the programs' expected_attach_type. Similarly, a program attached to BPF_CGROUP_INET4_GETPEERNAME should not be allowed doing a tailcall into a program which calls bpf_bind() out of BPF which is only enabled for BPF_CGROUP_INET4_CONNECT. In short, specifying expected_attach_type allows to open up additional functionality or",
    "evidence": "osv:CVE-2025-40123",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.270",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.221",
            "evidence": "/affected/1/ranges"
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          {
            "value": "6.1.156",
            "evidence": "/affected/1/ranges"
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          {
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            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
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          {
            "value": "6.17.3",
            "evidence": "/affected/1/ranges"
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        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-40123",
      "aliases": [
        "CVE-2025-40123"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-40123.json"
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              "type": "ECOSYSTEM",
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                  "introduced": "4.17.0"
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            "ecosystem": "Linux"
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      ],
      "modified": "2026-10-28T02:30:26.895281257Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/08cb3dc9d2b44f153d0bcf2cb966e4a94b5d0f32",
        "https://git.kernel.org/stable/c/4540aed51b12bc13364149bf95f6ecef013197c0",
        "https://git.kernel.org/stable/c/a99de19128aec0913f3d529f529fbbff5edfaff8",
        "https://git.kernel.org/stable/c/c1ad19b5d8e23123503dcaf2d4342e1b90b923ad",
        "https://git.kernel.org/stable/c/dc4f348952173beb8ceb15be30b249276eccb605",
        "https://git.kernel.org/stable/c/e53a59e7cee5c1605d1ed595933098c2b69108f9",
        "https://git.kernel.org/stable/c/f856c598080ba7ce1252867b8ecd6ad5bdaf9a6a",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/40xxx/CVE-2025-40123.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-40123",
        "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/2025/40xxx/CVE-2025-40123.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-40123",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 493562,
  "published_at": "2025-11-12T10:23:19.589+00:00"
}