156 lines
3.8 KiB
C
156 lines
3.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0
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* Copyright (c) 2018 Facebook
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*
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* This program shows how to use bpf_xdp_adjust_tail() by
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* generating ICMPv4 "packet to big" (unreachable/ df bit set frag needed
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* to be more preice in case of v4)" where receiving packets bigger then
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* 600 bytes.
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*/
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#define KBUILD_MODNAME "foo"
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#include <uapi/linux/bpf.h>
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#include <linux/in.h>
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#include <linux/if_ether.h>
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#include <linux/if_packet.h>
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#include <linux/if_vlan.h>
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#include <linux/ip.h>
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#include <linux/icmp.h>
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#include "bpf_helpers.h"
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#define DEFAULT_TTL 64
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#define MAX_PCKT_SIZE 600
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#define ICMP_TOOBIG_SIZE 98
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#define ICMP_TOOBIG_PAYLOAD_SIZE 92
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/* volatile to prevent compiler optimizations */
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static volatile __u32 max_pcktsz = MAX_PCKT_SIZE;
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struct {
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__uint(type, BPF_MAP_TYPE_ARRAY);
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__type(key, __u32);
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__type(value, __u64);
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__uint(max_entries, 1);
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} icmpcnt SEC(".maps");
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static __always_inline void count_icmp(void)
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{
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u64 key = 0;
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u64 *icmp_count;
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icmp_count = bpf_map_lookup_elem(&icmpcnt, &key);
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if (icmp_count)
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*icmp_count += 1;
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}
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static __always_inline void swap_mac(void *data, struct ethhdr *orig_eth)
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{
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struct ethhdr *eth;
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eth = data;
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memcpy(eth->h_source, orig_eth->h_dest, ETH_ALEN);
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memcpy(eth->h_dest, orig_eth->h_source, ETH_ALEN);
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eth->h_proto = orig_eth->h_proto;
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}
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static __always_inline __u16 csum_fold_helper(__u32 csum)
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{
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return ~((csum & 0xffff) + (csum >> 16));
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}
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static __always_inline void ipv4_csum(void *data_start, int data_size,
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__u32 *csum)
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{
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*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
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*csum = csum_fold_helper(*csum);
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}
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static __always_inline int send_icmp4_too_big(struct xdp_md *xdp)
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{
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int headroom = (int)sizeof(struct iphdr) + (int)sizeof(struct icmphdr);
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if (bpf_xdp_adjust_head(xdp, 0 - headroom))
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return XDP_DROP;
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void *data = (void *)(long)xdp->data;
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void *data_end = (void *)(long)xdp->data_end;
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if (data + (ICMP_TOOBIG_SIZE + headroom) > data_end)
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return XDP_DROP;
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struct iphdr *iph, *orig_iph;
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struct icmphdr *icmp_hdr;
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struct ethhdr *orig_eth;
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__u32 csum = 0;
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__u64 off = 0;
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orig_eth = data + headroom;
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swap_mac(data, orig_eth);
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off += sizeof(struct ethhdr);
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iph = data + off;
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off += sizeof(struct iphdr);
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icmp_hdr = data + off;
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off += sizeof(struct icmphdr);
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orig_iph = data + off;
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icmp_hdr->type = ICMP_DEST_UNREACH;
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icmp_hdr->code = ICMP_FRAG_NEEDED;
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icmp_hdr->un.frag.mtu = htons(max_pcktsz - sizeof(struct ethhdr));
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icmp_hdr->checksum = 0;
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ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);
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icmp_hdr->checksum = csum;
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iph->ttl = DEFAULT_TTL;
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iph->daddr = orig_iph->saddr;
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iph->saddr = orig_iph->daddr;
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iph->version = 4;
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iph->ihl = 5;
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iph->protocol = IPPROTO_ICMP;
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iph->tos = 0;
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iph->tot_len = htons(
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ICMP_TOOBIG_SIZE + headroom - sizeof(struct ethhdr));
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iph->check = 0;
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csum = 0;
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ipv4_csum(iph, sizeof(struct iphdr), &csum);
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iph->check = csum;
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count_icmp();
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return XDP_TX;
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}
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static __always_inline int handle_ipv4(struct xdp_md *xdp)
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{
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void *data_end = (void *)(long)xdp->data_end;
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void *data = (void *)(long)xdp->data;
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int pckt_size = data_end - data;
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int offset;
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if (pckt_size > max(max_pcktsz, ICMP_TOOBIG_SIZE)) {
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offset = pckt_size - ICMP_TOOBIG_SIZE;
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if (bpf_xdp_adjust_tail(xdp, 0 - offset))
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return XDP_PASS;
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return send_icmp4_too_big(xdp);
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}
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return XDP_PASS;
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}
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SEC("xdp_icmp")
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int _xdp_icmp(struct xdp_md *xdp)
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{
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void *data_end = (void *)(long)xdp->data_end;
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void *data = (void *)(long)xdp->data;
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struct ethhdr *eth = data;
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__u16 h_proto;
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if (eth + 1 > data_end)
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return XDP_DROP;
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h_proto = eth->h_proto;
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if (h_proto == htons(ETH_P_IP))
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return handle_ipv4(xdp);
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else
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return XDP_PASS;
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}
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char _license[] SEC("license") = "GPL";
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