CVE-2026-45886
published 2026-05-27CVE-2026-45886: 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…
high7
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.
Affected
8 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| linux | linux | — | — |
| linux | linux | >= 3f364222d032eea6b245780e845ad213dab28cdd < ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e | ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e |
| linux | linux | >= 3f364222d032eea6b245780e845ad213dab28cdd < ddc34a1b85505c919026ddc82fafdada9a160b15 | ddc34a1b85505c919026ddc82fafdada9a160b15 |
| linux | linux | >= 3f364222d032eea6b245780e845ad213dab28cdd < 0db169a91381a473b7974021d1c02f8da72c5775 | 0db169a91381a473b7974021d1c02f8da72c5775 |
| linux | linux | >= 3f364222d032eea6b245780e845ad213dab28cdd < d7b87adeb0eb539b9b824b101bb14fb01e41240b | d7b87adeb0eb539b9b824b101bb14fb01e41240b |
| linux | linux | >= 3f364222d032eea6b245780e845ad213dab28cdd < 57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52 | 57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52 |
| linux | linux | >= 3f364222d032eea6b245780e845ad213dab28cdd < 6557f1565d779851c4db9c488c49c05a47a6e72f | 6557f1565d779851c4db9c488c49c05a47a6e72f |
| linux | linux_kernel | — | — |