CVE-2026-45886
bpf: Fix bpf_xdp_store_bytes proto for read-only arg
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.
Fixes and workarounds
No remediation reported in collected sources.
Missing remediation information is not evidence that no patch exists.
Affected products and versions
| Product | Versions | Authority |
|---|---|---|
| Linux Linux |
≥ 3f364222d032eea6b245780e845ad213dab28cdd; < ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e (affected, git) ≥ 3f364222d032eea6b245780e845ad213dab28cdd; < ddc34a1b85505c919026ddc82fafdada9a160b15 (affected, git) ≥ 3f364222d032eea6b245780e845ad213dab28cdd; < 0db169a91381a473b7974021d1c02f8da72c5775 (affected, git) ≥ 3f364222d032eea6b245780e845ad213dab28cdd; < d7b87adeb0eb539b9b824b101bb14fb01e41240b (affected, git) ≥ 3f364222d032eea6b245780e845ad213dab28cdd; < 57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52 (affected, git) ≥ 3f364222d032eea6b245780e845ad213dab28cdd; < 6557f1565d779851c4db9c488c49c05a47a6e72f (affected, git) Other versions: unaffected |
CNA: Linux |
| Linux Linux |
5.18 (affected) ≥ 0; < 5.18 (unaffected, semver) ≥ 6.1.165; ≤ 6.1.* (unaffected, semver) ≥ 6.6.128; ≤ 6.6.* (unaffected, semver) ≥ 6.12.75; ≤ 6.12.* (unaffected, semver) ≥ 6.18.14; ≤ 6.18.* (unaffected, semver) ≥ 6.19.4; ≤ 6.19.* (unaffected, semver) ≥ 7.0; ≤ * (unaffected, original_commit_for_fix) Other versions: affected |
CNA: Linux |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
No CVSS assessment reported. An unscored record is not a low-severity determination.
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://git.kernel.org/stable/c/ffb5d1c5e3933b947fc7303ad68bf0c536d0c85eCNA: Linux
- https://git.kernel.org/stable/c/ddc34a1b85505c919026ddc82fafdada9a160b15CNA: Linux
- https://git.kernel.org/stable/c/0db169a91381a473b7974021d1c02f8da72c5775CNA: Linux
- https://git.kernel.org/stable/c/d7b87adeb0eb539b9b824b101bb14fb01e41240bCNA: Linux
- https://git.kernel.org/stable/c/57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52CNA: Linux
- https://git.kernel.org/stable/c/6557f1565d779851c4db9c488c49c05a47a6e72fCNA: Linux
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