CVE-2026-45886

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> bpf: Fix bpf_xdp_store_bytes proto for read-only arg<br /> <br /> While making some maps in Cilium read-only from the BPF side, we noticed<br /> that the bpf_xdp_store_bytes proto is incorrect. In particular, the<br /> verifier was throwing the following error:<br /> <br /> ; ret = ctx_store_bytes(ctx, l3_off + offsetof(struct iphdr, saddr),<br /> &amp;nat-&gt;address, 4, 0);<br /> 635: (79) r1 = *(u64 *)(r10 -144) ; R1=ctx() R10=fp0 fp-144=ctx()<br /> 636: (b4) w2 = 26 ; R2=26<br /> 637: (b4) w4 = 4 ; R4=4<br /> 638: (b4) w5 = 0 ; R5=0<br /> 639: (85) call bpf_xdp_store_bytes#190<br /> write into map forbidden, value_size=6 off=0 size=4<br /> <br /> nat comes from a BPF_F_RDONLY_PROG map, so R3 is a PTR_TO_MAP_VALUE.<br /> The verifier checks the helper&amp;#39;s memory access to R3 in<br /> check_mem_size_reg, as it reaches ARG_CONST_SIZE argument. The third<br /> argument has expected type ARG_PTR_TO_UNINIT_MEM, which includes the<br /> MEM_WRITE flag. The verifier thus checks for a BPF_WRITE access on R3.<br /> Given R3 points to a read-only map, the check fails.<br /> <br /> Conversely, ARG_PTR_TO_UNINIT_MEM can also lead to the helper reading<br /> from uninitialized memory.<br /> <br /> This patch simply fixes the expected argument type to match that of<br /> bpf_skb_store_bytes.