// SPDX-License-Identifier: GPL-2.0 /* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ #include "vmlinux.h" #include "bpf_tracing_net.h" #include <bpf/bpf_helpers.h> #include <bpf/bpf_endian.h> #define UDP_TEST_PORT 7777 void *bpf_cast_to_kern_ctx(void *) __ksym; bool had_dst = false; bool dst_cleared = false; SEC("tc/egress") int dst_clear(struct __sk_buff *skb) { struct sk_buff *kskb; struct iphdr iph; struct udphdr udph; int err; if (skb->protocol != __bpf_constant_htons(ETH_P_IP)) return TC_ACT_OK; if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph, sizeof(iph))) return TC_ACT_OK; if (iph.protocol != IPPROTO_UDP) return TC_ACT_OK; if (bpf_skb_load_bytes(skb, ETH_HLEN + sizeof(iph), &udph, sizeof(udph))) return TC_ACT_OK; if (udph.dest != __bpf_constant_htons(UDP_TEST_PORT)) return TC_ACT_OK; kskb = bpf_cast_to_kern_ctx(skb); had_dst = (kskb->_skb_refdst != 0); /* Same-protocol encap (IPIP): protocol stays IPv4, but the dst * from the original routing is no longer valid for the outer hdr. */ err = bpf_skb_adjust_room(skb, (s32)sizeof(struct iphdr), BPF_ADJ_ROOM_MAC, BPF_F_ADJ_ROOM_FIXED_GSO | BPF_F_ADJ_ROOM_ENCAP_L3_IPV4); if (err) return TC_ACT_SHOT; dst_cleared = (kskb->_skb_refdst == 0); return TC_ACT_SHOT; } char __license[] SEC("license") = "GPL";