bpf: Fix bpf_xdp_store_bytes proto for read-only arg

{
  "id": "1a9d4e61e3e5281c7c11032ea17e1e59769a30aa2091693725e484438b7b139b",
  "url": "https://osv.dev/vulnerability/CVE-2026-45886",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "bpf: Fix bpf_xdp_store_bytes proto for read-only arg",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: bpf: Fix bpf_xdp_store_bytes proto for read-only arg While making some maps in Cilium read-only from the BPF side, we noticed that the bpf_xdp_store_bytes proto is incorrect. In particular, the verifier was throwing the following error: ; ret = ctx_store_bytes(ctx, l3_off + offsetof(struct iphdr, saddr), &nat->address, 4, 0); 635: (79) r1 = *(u64 *)(r10 -144) ; R1=ctx() R10=fp0 fp-144=ctx() 636: (b4) w2 = 26 ; R2=26 637: (b4) w4 = 4 ; R4=4 638: (b4) w5 = 0 ; R5=0 639: (85) call bpf_xdp_store_bytes#190 write into map forbidden, value_size=6 off=0 size=4 nat comes from a BPF_F_RDONLY_PROG map, so R3 is a PTR_TO_MAP_VALUE. The verifier checks the helper's memory access to R3 in check_mem_size_reg, as it reaches ARG_CONST_SIZE argument. The third argument has expected type ARG_PTR_TO_UNINIT_MEM, which includes the MEM_WRITE flag. The verifier thus checks for a BPF_WRITE access on R3. Given R3 points to a read-only map, the check fails. Conversely, ARG_PTR_TO_UNINIT_MEM can also lead to the helper reading from uninitialized memory. This patch simply fixes the expected argument type to match that of bpf_skb_store_bytes.",
    "evidence": "osv:CVE-2026-45886",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.165",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.128",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.75",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.14",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.4",
            "evidence": "/affected/1/ranges"
          }
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        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-45886",
      "aliases": [
        "CVE-2026-45886"
      ],
      "affected": [
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                  "fixed": "d7b87adeb0eb539b9b824b101bb14fb01e41240b"
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                {
                  "fixed": "57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52"
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                  "fixed": "6557f1565d779851c4db9c488c49c05a47a6e72f"
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
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            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-45886.json"
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      ],
      "modified": "2026-10-28T02:30:37.951668169Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0db169a91381a473b7974021d1c02f8da72c5775",
        "https://git.kernel.org/stable/c/57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52",
        "https://git.kernel.org/stable/c/6557f1565d779851c4db9c488c49c05a47a6e72f",
        "https://git.kernel.org/stable/c/d7b87adeb0eb539b9b824b101bb14fb01e41240b",
        "https://git.kernel.org/stable/c/ddc34a1b85505c919026ddc82fafdada9a160b15",
        "https://git.kernel.org/stable/c/ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45886.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-45886",
        "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/2026/45xxx/CVE-2026-45886.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-45886",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 505055,
  "published_at": "2026-05-27T12:16:58+00:00"
}