1 // SPDX-License-Identifier: GPL-2.0 2 /* 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 7777 10 11 void *bpf_cast_to_kern_ctx(void *) __ksym; 12 bool init_csum_partial = false; 13 bool final_csum_none = false; 14 bool broken_csum_start = false; 15 16 static unsigned int skb_headlen(const struct sk_buff *skb) 17 { 18 return skb->len - skb->data_len; 19 } 20 21 static unsigned int skb_headroom(const struct sk_buff *skb) 22 { 23 return skb->data - skb->head; 24 } 25 26 static int skb_checksum_start_offset(const struct sk_buff *skb) 27 { 28 return skb->csum_start - skb_headroom(skb); 29 } 30 31 SEC("tc") 32 int 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 68 char __license[] SEC("license") = "GPL"; 69