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// 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* from the original routing is no longer valid for the outer hdr.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";
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