mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-06 02:24:14 +08:00
c6ffd1ff78
adding bpf's sample program which is using bpf_xdp_adjust_tail helper by generating ICMPv4 "packet to big" message if ingress packet's size is bigger then 600 bytes Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
153 lines
3.7 KiB
C
153 lines
3.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0
|
|
* Copyright (c) 2018 Facebook
|
|
*
|
|
* This program is free software; you can redistribute it and/or
|
|
* modify it under the terms of version 2 of the GNU General Public
|
|
* License as published by the Free Software Foundation.
|
|
*
|
|
* This program shows how to use bpf_xdp_adjust_tail() by
|
|
* generating ICMPv4 "packet to big" (unreachable/ df bit set frag needed
|
|
* to be more preice in case of v4)" where receiving packets bigger then
|
|
* 600 bytes.
|
|
*/
|
|
#define KBUILD_MODNAME "foo"
|
|
#include <uapi/linux/bpf.h>
|
|
#include <linux/in.h>
|
|
#include <linux/if_ether.h>
|
|
#include <linux/if_packet.h>
|
|
#include <linux/if_vlan.h>
|
|
#include <linux/ip.h>
|
|
#include <linux/icmp.h>
|
|
#include "bpf_helpers.h"
|
|
|
|
#define DEFAULT_TTL 64
|
|
#define MAX_PCKT_SIZE 600
|
|
#define ICMP_TOOBIG_SIZE 98
|
|
#define ICMP_TOOBIG_PAYLOAD_SIZE 92
|
|
|
|
struct bpf_map_def SEC("maps") icmpcnt = {
|
|
.type = BPF_MAP_TYPE_ARRAY,
|
|
.key_size = sizeof(__u32),
|
|
.value_size = sizeof(__u64),
|
|
.max_entries = 1,
|
|
};
|
|
|
|
static __always_inline void count_icmp(void)
|
|
{
|
|
u64 key = 0;
|
|
u64 *icmp_count;
|
|
|
|
icmp_count = bpf_map_lookup_elem(&icmpcnt, &key);
|
|
if (icmp_count)
|
|
*icmp_count += 1;
|
|
}
|
|
|
|
static __always_inline void swap_mac(void *data, struct ethhdr *orig_eth)
|
|
{
|
|
struct ethhdr *eth;
|
|
|
|
eth = data;
|
|
memcpy(eth->h_source, orig_eth->h_dest, ETH_ALEN);
|
|
memcpy(eth->h_dest, orig_eth->h_source, ETH_ALEN);
|
|
eth->h_proto = orig_eth->h_proto;
|
|
}
|
|
|
|
static __always_inline __u16 csum_fold_helper(__u32 csum)
|
|
{
|
|
return ~((csum & 0xffff) + (csum >> 16));
|
|
}
|
|
|
|
static __always_inline void ipv4_csum(void *data_start, int data_size,
|
|
__u32 *csum)
|
|
{
|
|
*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
|
|
*csum = csum_fold_helper(*csum);
|
|
}
|
|
|
|
static __always_inline int send_icmp4_too_big(struct xdp_md *xdp)
|
|
{
|
|
int headroom = (int)sizeof(struct iphdr) + (int)sizeof(struct icmphdr);
|
|
|
|
if (bpf_xdp_adjust_head(xdp, 0 - headroom))
|
|
return XDP_DROP;
|
|
void *data = (void *)(long)xdp->data;
|
|
void *data_end = (void *)(long)xdp->data_end;
|
|
|
|
if (data + (ICMP_TOOBIG_SIZE + headroom) > data_end)
|
|
return XDP_DROP;
|
|
|
|
struct iphdr *iph, *orig_iph;
|
|
struct icmphdr *icmp_hdr;
|
|
struct ethhdr *orig_eth;
|
|
__u32 csum = 0;
|
|
__u64 off = 0;
|
|
|
|
orig_eth = data + headroom;
|
|
swap_mac(data, orig_eth);
|
|
off += sizeof(struct ethhdr);
|
|
iph = data + off;
|
|
off += sizeof(struct iphdr);
|
|
icmp_hdr = data + off;
|
|
off += sizeof(struct icmphdr);
|
|
orig_iph = data + off;
|
|
icmp_hdr->type = ICMP_DEST_UNREACH;
|
|
icmp_hdr->code = ICMP_FRAG_NEEDED;
|
|
icmp_hdr->un.frag.mtu = htons(MAX_PCKT_SIZE-sizeof(struct ethhdr));
|
|
icmp_hdr->checksum = 0;
|
|
ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);
|
|
icmp_hdr->checksum = csum;
|
|
iph->ttl = DEFAULT_TTL;
|
|
iph->daddr = orig_iph->saddr;
|
|
iph->saddr = orig_iph->daddr;
|
|
iph->version = 4;
|
|
iph->ihl = 5;
|
|
iph->protocol = IPPROTO_ICMP;
|
|
iph->tos = 0;
|
|
iph->tot_len = htons(
|
|
ICMP_TOOBIG_SIZE + headroom - sizeof(struct ethhdr));
|
|
iph->check = 0;
|
|
csum = 0;
|
|
ipv4_csum(iph, sizeof(struct iphdr), &csum);
|
|
iph->check = csum;
|
|
count_icmp();
|
|
return XDP_TX;
|
|
}
|
|
|
|
|
|
static __always_inline int handle_ipv4(struct xdp_md *xdp)
|
|
{
|
|
void *data_end = (void *)(long)xdp->data_end;
|
|
void *data = (void *)(long)xdp->data;
|
|
int pckt_size = data_end - data;
|
|
int offset;
|
|
|
|
if (pckt_size > MAX_PCKT_SIZE) {
|
|
offset = pckt_size - ICMP_TOOBIG_SIZE;
|
|
if (bpf_xdp_adjust_tail(xdp, 0 - offset))
|
|
return XDP_PASS;
|
|
return send_icmp4_too_big(xdp);
|
|
}
|
|
return XDP_PASS;
|
|
}
|
|
|
|
SEC("xdp_icmp")
|
|
int _xdp_icmp(struct xdp_md *xdp)
|
|
{
|
|
void *data_end = (void *)(long)xdp->data_end;
|
|
void *data = (void *)(long)xdp->data;
|
|
struct ethhdr *eth = data;
|
|
__u16 h_proto;
|
|
|
|
if (eth + 1 > data_end)
|
|
return XDP_DROP;
|
|
|
|
h_proto = eth->h_proto;
|
|
|
|
if (h_proto == htons(ETH_P_IP))
|
|
return handle_ipv4(xdp);
|
|
else
|
|
return XDP_PASS;
|
|
}
|
|
|
|
char _license[] SEC("license") = "GPL";
|