bpf: add bpf_xdp_adjust_tail sample prog

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>
This commit is contained in:
Nikita V. Shirokov 2018-04-17 21:42:23 -07:00 committed by Daniel Borkmann
parent 0367d0a294
commit c6ffd1ff78
4 changed files with 300 additions and 0 deletions

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@ -44,6 +44,7 @@ hostprogs-y += xdp_monitor
hostprogs-y += xdp_rxq_info
hostprogs-y += syscall_tp
hostprogs-y += cpustat
hostprogs-y += xdp_adjust_tail
# Libbpf dependencies
LIBBPF := ../../tools/lib/bpf/bpf.o ../../tools/lib/bpf/nlattr.o
@ -95,6 +96,7 @@ xdp_monitor-objs := bpf_load.o $(LIBBPF) xdp_monitor_user.o
xdp_rxq_info-objs := bpf_load.o $(LIBBPF) xdp_rxq_info_user.o
syscall_tp-objs := bpf_load.o $(LIBBPF) syscall_tp_user.o
cpustat-objs := bpf_load.o $(LIBBPF) cpustat_user.o
xdp_adjust_tail-objs := bpf_load.o $(LIBBPF) xdp_adjust_tail_user.o
# Tell kbuild to always build the programs
always := $(hostprogs-y)
@ -148,6 +150,7 @@ always += xdp_rxq_info_kern.o
always += xdp2skb_meta_kern.o
always += syscall_tp_kern.o
always += cpustat_kern.o
always += xdp_adjust_tail_kern.o
HOSTCFLAGS += -I$(objtree)/usr/include
HOSTCFLAGS += -I$(srctree)/tools/lib/
@ -193,6 +196,7 @@ HOSTLOADLIBES_xdp_monitor += -lelf
HOSTLOADLIBES_xdp_rxq_info += -lelf
HOSTLOADLIBES_syscall_tp += -lelf
HOSTLOADLIBES_cpustat += -lelf
HOSTLOADLIBES_xdp_adjust_tail += -lelf
# Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
# make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang

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@ -0,0 +1,152 @@
/* 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";

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@ -0,0 +1,142 @@
/* 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.
*/
#include <linux/bpf.h>
#include <linux/if_link.h>
#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/resource.h>
#include <arpa/inet.h>
#include <netinet/ether.h>
#include <unistd.h>
#include <time.h>
#include "bpf_load.h"
#include "libbpf.h"
#include "bpf_util.h"
#define STATS_INTERVAL_S 2U
static int ifindex = -1;
static __u32 xdp_flags;
static void int_exit(int sig)
{
if (ifindex > -1)
bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
exit(0);
}
/* simple "icmp packet too big sent" counter
*/
static void poll_stats(unsigned int kill_after_s)
{
time_t started_at = time(NULL);
__u64 value = 0;
int key = 0;
while (!kill_after_s || time(NULL) - started_at <= kill_after_s) {
sleep(STATS_INTERVAL_S);
assert(bpf_map_lookup_elem(map_fd[0], &key, &value) == 0);
printf("icmp \"packet too big\" sent: %10llu pkts\n", value);
}
}
static void usage(const char *cmd)
{
printf("Start a XDP prog which send ICMP \"packet too big\" \n"
"messages if ingress packet is bigger then MAX_SIZE bytes\n");
printf("Usage: %s [...]\n", cmd);
printf(" -i <ifindex> Interface Index\n");
printf(" -T <stop-after-X-seconds> Default: 0 (forever)\n");
printf(" -S use skb-mode\n");
printf(" -N enforce native mode\n");
printf(" -h Display this help\n");
}
int main(int argc, char **argv)
{
unsigned char opt_flags[256] = {};
unsigned int kill_after_s = 0;
const char *optstr = "i:T:SNh";
struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
char filename[256];
int opt;
int i;
for (i = 0; i < strlen(optstr); i++)
if (optstr[i] != 'h' && 'a' <= optstr[i] && optstr[i] <= 'z')
opt_flags[(unsigned char)optstr[i]] = 1;
while ((opt = getopt(argc, argv, optstr)) != -1) {
switch (opt) {
case 'i':
ifindex = atoi(optarg);
break;
case 'T':
kill_after_s = atoi(optarg);
break;
case 'S':
xdp_flags |= XDP_FLAGS_SKB_MODE;
break;
case 'N':
xdp_flags |= XDP_FLAGS_DRV_MODE;
break;
default:
usage(argv[0]);
return 1;
}
opt_flags[opt] = 0;
}
for (i = 0; i < strlen(optstr); i++) {
if (opt_flags[(unsigned int)optstr[i]]) {
fprintf(stderr, "Missing argument -%c\n", optstr[i]);
usage(argv[0]);
return 1;
}
}
if (setrlimit(RLIMIT_MEMLOCK, &r)) {
perror("setrlimit(RLIMIT_MEMLOCK, RLIM_INFINITY)");
return 1;
}
snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
if (load_bpf_file(filename)) {
printf("%s", bpf_log_buf);
return 1;
}
if (!prog_fd[0]) {
printf("load_bpf_file: %s\n", strerror(errno));
return 1;
}
signal(SIGINT, int_exit);
signal(SIGTERM, int_exit);
if (bpf_set_link_xdp_fd(ifindex, prog_fd[0], xdp_flags) < 0) {
printf("link set xdp fd failed\n");
return 1;
}
poll_stats(kill_after_s);
bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
return 0;
}

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@ -132,6 +132,8 @@ static int (*bpf_l3_csum_replace)(void *ctx, int off, int from, int to, int flag
(void *) BPF_FUNC_l3_csum_replace;
static int (*bpf_l4_csum_replace)(void *ctx, int off, int from, int to, int flags) =
(void *) BPF_FUNC_l4_csum_replace;
static int (*bpf_csum_diff)(void *from, int from_size, void *to, int to_size, int seed) =
(void *) BPF_FUNC_csum_diff;
static int (*bpf_skb_under_cgroup)(void *ctx, void *map, int index) =
(void *) BPF_FUNC_skb_under_cgroup;
static int (*bpf_skb_change_head)(void *, int len, int flags) =