GHSA-W77R-V3RV-5RCP
Vulnerability from github – Published: 2026-05-27 15:33 – Updated: 2026-05-27 15:33In 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.
{
"affected": [],
"aliases": [
"CVE-2026-45886"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-05-27T14:17:02Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix bpf_xdp_store_bytes proto for read-only arg\n\nWhile making some maps in Cilium read-only from the BPF side, we noticed\nthat the bpf_xdp_store_bytes proto is incorrect. In particular, the\nverifier was throwing the following error:\n\n ; ret = ctx_store_bytes(ctx, l3_off + offsetof(struct iphdr, saddr),\n \u0026nat-\u003eaddress, 4, 0);\n 635: (79) r1 = *(u64 *)(r10 -144) ; R1=ctx() R10=fp0 fp-144=ctx()\n 636: (b4) w2 = 26 ; R2=26\n 637: (b4) w4 = 4 ; R4=4\n 638: (b4) w5 = 0 ; R5=0\n 639: (85) call bpf_xdp_store_bytes#190\n write into map forbidden, value_size=6 off=0 size=4\n\nnat comes from a BPF_F_RDONLY_PROG map, so R3 is a PTR_TO_MAP_VALUE.\nThe verifier checks the helper\u0027s memory access to R3 in\ncheck_mem_size_reg, as it reaches ARG_CONST_SIZE argument. The third\nargument has expected type ARG_PTR_TO_UNINIT_MEM, which includes the\nMEM_WRITE flag. The verifier thus checks for a BPF_WRITE access on R3.\nGiven R3 points to a read-only map, the check fails.\n\nConversely, ARG_PTR_TO_UNINIT_MEM can also lead to the helper reading\nfrom uninitialized memory.\n\nThis patch simply fixes the expected argument type to match that of\nbpf_skb_store_bytes.",
"id": "GHSA-w77r-v3rv-5rcp",
"modified": "2026-05-27T15:33:15Z",
"published": "2026-05-27T15:33:14Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-45886"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0db169a91381a473b7974021d1c02f8da72c5775"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6557f1565d779851c4db9c488c49c05a47a6e72f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d7b87adeb0eb539b9b824b101bb14fb01e41240b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ddc34a1b85505c919026ddc82fafdada9a160b15"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
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