1 /* SPDX-License-Identifier: GPL-2.0
2 * Copyright (c) 2018 Facebook
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of version 2 of the GNU General Public
6 * License as published by the Free Software Foundation.
8 * This program shows how to use bpf_xdp_adjust_tail() by
9 * generating ICMPv4 "packet to big" (unreachable/ df bit set frag needed
10 * to be more preice in case of v4)" where receiving packets bigger then
13 #define KBUILD_MODNAME "foo"
14 #include <uapi/linux/bpf.h>
16 #include <linux/if_ether.h>
17 #include <linux/if_packet.h>
18 #include <linux/if_vlan.h>
20 #include <linux/icmp.h>
21 #include "bpf_helpers.h"
23 #define DEFAULT_TTL 64
24 #define MAX_PCKT_SIZE 600
25 #define ICMP_TOOBIG_SIZE 98
26 #define ICMP_TOOBIG_PAYLOAD_SIZE 92
29 __uint(type, BPF_MAP_TYPE_ARRAY);
32 __uint(max_entries, 1);
33 } icmpcnt SEC(".maps");
35 static __always_inline void count_icmp(void)
40 icmp_count = bpf_map_lookup_elem(&icmpcnt, &key);
45 static __always_inline void swap_mac(void *data, struct ethhdr *orig_eth)
50 memcpy(eth->h_source, orig_eth->h_dest, ETH_ALEN);
51 memcpy(eth->h_dest, orig_eth->h_source, ETH_ALEN);
52 eth->h_proto = orig_eth->h_proto;
55 static __always_inline __u16 csum_fold_helper(__u32 csum)
57 return ~((csum & 0xffff) + (csum >> 16));
60 static __always_inline void ipv4_csum(void *data_start, int data_size,
63 *csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
64 *csum = csum_fold_helper(*csum);
67 static __always_inline int send_icmp4_too_big(struct xdp_md *xdp)
69 int headroom = (int)sizeof(struct iphdr) + (int)sizeof(struct icmphdr);
71 if (bpf_xdp_adjust_head(xdp, 0 - headroom))
73 void *data = (void *)(long)xdp->data;
74 void *data_end = (void *)(long)xdp->data_end;
76 if (data + (ICMP_TOOBIG_SIZE + headroom) > data_end)
79 struct iphdr *iph, *orig_iph;
80 struct icmphdr *icmp_hdr;
81 struct ethhdr *orig_eth;
85 orig_eth = data + headroom;
86 swap_mac(data, orig_eth);
87 off += sizeof(struct ethhdr);
89 off += sizeof(struct iphdr);
90 icmp_hdr = data + off;
91 off += sizeof(struct icmphdr);
92 orig_iph = data + off;
93 icmp_hdr->type = ICMP_DEST_UNREACH;
94 icmp_hdr->code = ICMP_FRAG_NEEDED;
95 icmp_hdr->un.frag.mtu = htons(MAX_PCKT_SIZE-sizeof(struct ethhdr));
96 icmp_hdr->checksum = 0;
97 ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);
98 icmp_hdr->checksum = csum;
99 iph->ttl = DEFAULT_TTL;
100 iph->daddr = orig_iph->saddr;
101 iph->saddr = orig_iph->daddr;
104 iph->protocol = IPPROTO_ICMP;
106 iph->tot_len = htons(
107 ICMP_TOOBIG_SIZE + headroom - sizeof(struct ethhdr));
110 ipv4_csum(iph, sizeof(struct iphdr), &csum);
117 static __always_inline int handle_ipv4(struct xdp_md *xdp)
119 void *data_end = (void *)(long)xdp->data_end;
120 void *data = (void *)(long)xdp->data;
121 int pckt_size = data_end - data;
124 if (pckt_size > MAX_PCKT_SIZE) {
125 offset = pckt_size - ICMP_TOOBIG_SIZE;
126 if (bpf_xdp_adjust_tail(xdp, 0 - offset))
128 return send_icmp4_too_big(xdp);
134 int _xdp_icmp(struct xdp_md *xdp)
136 void *data_end = (void *)(long)xdp->data_end;
137 void *data = (void *)(long)xdp->data;
138 struct ethhdr *eth = data;
141 if (eth + 1 > data_end)
144 h_proto = eth->h_proto;
146 if (h_proto == htons(ETH_P_IP))
147 return handle_ipv4(xdp);
152 char _license[] SEC("license") = "GPL";