| 1 | // SPDX-License-Identifier: GPL-2.0 |
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| 2 | /* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */ |
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| 3 | |
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| 4 | #include "vmlinux.h" |
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| 5 | #include "bpf_tracing_net.h" |
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| 6 | #include <bpf/bpf_helpers.h> |
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| 7 | #include <bpf/bpf_endian.h> |
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| 8 | |
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| 9 | #define UDP_TEST_PORT 7777 |
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| 10 | |
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| 11 | void *bpf_cast_to_kern_ctx(void *) __ksym; |
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| 12 | bool init_csum_partial = false; |
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| 13 | bool final_csum_none = false; |
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| 14 | bool broken_csum_start = false; |
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| 15 | |
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| 16 | static unsigned int skb_headlen(const struct sk_buff *skb) |
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| 17 | { |
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| 18 | return skb->len - skb->data_len; |
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| 19 | } |
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| 20 | |
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| 21 | static unsigned int skb_headroom(const struct sk_buff *skb) |
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| 22 | { |
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| 23 | return skb->data - skb->head; |
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| 24 | } |
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| 25 | |
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| 26 | static int skb_checksum_start_offset(const struct sk_buff *skb) |
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| 27 | { |
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| 28 | return skb->csum_start - skb_headroom(skb); |
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| 29 | } |
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| 30 | |
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| 31 | SEC("tc" ) |
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| 32 | int decap_sanity(struct __sk_buff *skb) |
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| 33 | { |
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| 34 | struct sk_buff *kskb; |
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| 35 | struct ipv6hdr ip6h; |
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| 36 | struct udphdr udph; |
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| 37 | int err; |
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| 38 | |
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| 39 | if (skb->protocol != __bpf_constant_htons(ETH_P_IPV6)) |
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| 40 | return TC_ACT_SHOT; |
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| 41 | |
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| 42 | if (bpf_skb_load_bytes(skb, ETH_HLEN, &ip6h, sizeof(ip6h))) |
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| 43 | return TC_ACT_SHOT; |
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| 44 | |
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| 45 | if (ip6h.nexthdr != IPPROTO_UDP) |
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| 46 | return TC_ACT_SHOT; |
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| 47 | |
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| 48 | if (bpf_skb_load_bytes(skb, ETH_HLEN + sizeof(ip6h), &udph, sizeof(udph))) |
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| 49 | return TC_ACT_SHOT; |
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| 50 | |
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| 51 | if (udph.dest != __bpf_constant_htons(UDP_TEST_PORT)) |
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| 52 | return TC_ACT_SHOT; |
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| 53 | |
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| 54 | kskb = bpf_cast_to_kern_ctx(skb); |
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| 55 | init_csum_partial = (kskb->ip_summed == CHECKSUM_PARTIAL); |
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| 56 | err = bpf_skb_adjust_room(skb, -(s32)(ETH_HLEN + sizeof(ip6h) + sizeof(udph)), |
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| 57 | 1, BPF_F_ADJ_ROOM_FIXED_GSO); |
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| 58 | if (err) |
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| 59 | return TC_ACT_SHOT; |
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| 60 | final_csum_none = (kskb->ip_summed == CHECKSUM_NONE); |
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| 61 | if (kskb->ip_summed == CHECKSUM_PARTIAL && |
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| 62 | (unsigned int)skb_checksum_start_offset(skb: kskb) >= skb_headlen(skb: kskb)) |
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| 63 | broken_csum_start = true; |
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| 64 | |
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| 65 | return TC_ACT_SHOT; |
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| 66 | } |
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| 67 | |
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| 68 | char __license[] SEC("license" ) = "GPL" ; |
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| 69 | |
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