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
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