69 lines · c
1// SPDX-License-Identifier: GPL-2.02/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */3 4#include "vmlinux.h"5#include "bpf_tracing_net.h"6#include <bpf/bpf_helpers.h>7#include <bpf/bpf_endian.h>8 9#define UDP_TEST_PORT 777710 11void *bpf_cast_to_kern_ctx(void *) __ksym;12bool init_csum_partial = false;13bool final_csum_none = false;14bool broken_csum_start = false;15 16static unsigned int skb_headlen(const struct sk_buff *skb)17{18 return skb->len - skb->data_len;19}20 21static unsigned int skb_headroom(const struct sk_buff *skb)22{23 return skb->data - skb->head;24}25 26static int skb_checksum_start_offset(const struct sk_buff *skb)27{28 return skb->csum_start - skb_headroom(skb);29}30 31SEC("tc")32int decap_sanity(struct __sk_buff *skb)33{34 struct sk_buff *kskb;35 struct ipv6hdr ip6h;36 struct udphdr udph;37 int err;38 39 if (skb->protocol != __bpf_constant_htons(ETH_P_IPV6))40 return TC_ACT_SHOT;41 42 if (bpf_skb_load_bytes(skb, ETH_HLEN, &ip6h, sizeof(ip6h)))43 return TC_ACT_SHOT;44 45 if (ip6h.nexthdr != IPPROTO_UDP)46 return TC_ACT_SHOT;47 48 if (bpf_skb_load_bytes(skb, ETH_HLEN + sizeof(ip6h), &udph, sizeof(udph)))49 return TC_ACT_SHOT;50 51 if (udph.dest != __bpf_constant_htons(UDP_TEST_PORT))52 return TC_ACT_SHOT;53 54 kskb = bpf_cast_to_kern_ctx(skb);55 init_csum_partial = (kskb->ip_summed == CHECKSUM_PARTIAL);56 err = bpf_skb_adjust_room(skb, -(s32)(ETH_HLEN + sizeof(ip6h) + sizeof(udph)),57 1, BPF_F_ADJ_ROOM_FIXED_GSO);58 if (err)59 return TC_ACT_SHOT;60 final_csum_none = (kskb->ip_summed == CHECKSUM_NONE);61 if (kskb->ip_summed == CHECKSUM_PARTIAL &&62 (unsigned int)skb_checksum_start_offset(kskb) >= skb_headlen(kskb))63 broken_csum_start = true;64 65 return TC_ACT_SHOT;66}67 68char __license[] SEC("license") = "GPL";69