From e4a62833adff6ef0fe7c0b90393204fe3c26b5c5 Mon Sep 17 00:00:00 2001 From: Weiming Shi Date: Wed, 9 Sep 2026 12:08:08 +0800 Subject: [PATCH] bpf: Disallow bpf_skb_pull_data() for LWT_SEG6LOCAL An LWT_SEG6LOCAL program can invalidate its cached SRH with bpf_lwt_seg6_adjust_srh() and then call bpf_skb_pull_data(). The latter may reallocate skb->head, leaving the per-CPU SRH pointer dangling. Post-program SRH validation then writes through that pointer. Disallow bpf_skb_pull_data() for LWT_SEG6LOCAL programs so the verifier rejects this unsafe helper combination. Other LWT program types continue to expose the helper through lwt_out_func_proto(). Fixes: 004d4b274e2a ("ipv6: sr: Add seg6local action End.BPF") Reported-by: co+adfca3e91be95776@bugs.sh Suggested-by: Alexei Starovoitov Signed-off-by: Weiming Shi Signed-off-by: Daniel Borkmann Reviewed-by: Emil Tsalapatis Closes: https://lore.kernel.org/all/GCy0KRM2IcQGoJQTjJEU9D0maBxXzEDHuQpq@bugs.sh/ Link: https://lore.kernel.org/bpf/DL9COXZQXX4V.1FN45QO2Q77ZH@gmail.com/ Link: https://lore.kernel.org/bpf/20260909040807.3885815-2-bestswngs@gmail.com --- net/core/filter.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/core/filter.c b/net/core/filter.c index 8513167a858a..2a84f9d01131 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -9044,6 +9044,8 @@ static const struct bpf_func_proto * lwt_seg6local_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) { switch (func_id) { + case BPF_FUNC_skb_pull_data: + return NULL; #if IS_ENABLED(CONFIG_IPV6_SEG6_BPF) case BPF_FUNC_lwt_seg6_store_bytes: return &bpf_lwt_seg6_store_bytes_proto;