samples/bpf/sock_example.c

   1 /* eBPF example program:
   2  * - creates arraymap in kernel with key 4 bytes and value 8 bytes
   3  *
   4  * - loads eBPF program:
   5  *   r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)];
   6  *   *(u32*)(fp - 4) = r0;
   7  *   // assuming packet is IPv4, lookup ip->proto in a map
   8  *   value = bpf_map_lookup_elem(map_fd, fp - 4);
   9  *   if (value)
  10  *        (*(u64*)value) += 1;
  11  *
  12  * - attaches this program to eth0 raw socket
  13  *
  14  * - every second user space reads map[tcp], map[udp], map[icmp] to see
  15  *   how many packets of given protocol were seen on eth0
  16  */
  17 #include <stdio.h>
  18 #include <unistd.h>
  19 #include <assert.h>
  20 #include <linux/bpf.h>
  21 #include <string.h>
  22 #include <stdlib.h>
  23 #include <errno.h>
  24 #include <sys/socket.h>
  25 #include <arpa/inet.h>
  26 #include <linux/if_ether.h>
  27 #include <linux/ip.h>
  28 #include <stddef.h>
  29 #include "libbpf.h"
  30 #include "sock_example.h"
  31
  32 char bpf_log_buf[BPF_LOG_BUF_SIZE];
  33
  34 static int test_sock(void)
  35 {
  36         int sock = -1, map_fd, prog_fd, i, key;
  37         long long value = 0, tcp_cnt, udp_cnt, icmp_cnt;
  38
  39         map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key), sizeof(value),
  40                                 256, 0);
  41         if (map_fd < 0) {
  42                 printf("failed to create map '%s'\n", strerror(errno));
  43                 goto cleanup;
  44         }
  45
  46         struct bpf_insn prog[] = {
  47                 BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
  48                 BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol) /* R0 = ip->proto */),
  49                 BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
  50                 BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
  51                 BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
  52                 BPF_LD_MAP_FD(BPF_REG_1, map_fd),
  53                 BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
  54                 BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
  55                 BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
  56                 BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
  57                 BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */
  58                 BPF_EXIT_INSN(),
  59         };
  60         size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);
  61
  62         prog_fd = bpf_load_program(BPF_PROG_TYPE_SOCKET_FILTER, prog, insns_cnt,
  63                                    "GPL", 0, bpf_log_buf, BPF_LOG_BUF_SIZE);
  64         if (prog_fd < 0) {
  65                 printf("failed to load prog '%s'\n", strerror(errno));
  66                 goto cleanup;
  67         }
  68
  69         sock = open_raw_sock("lo");
  70
  71         if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd,
  72                        sizeof(prog_fd)) < 0) {
  73                 printf("setsockopt %s\n", strerror(errno));
  74                 goto cleanup;
  75         }
  76
  77         for (i = 0; i < 10; i++) {
  78                 key = IPPROTO_TCP;
  79                 assert(bpf_map_lookup_elem(map_fd, &key, &tcp_cnt) == 0);
  80
  81                 key = IPPROTO_UDP;
  82                 assert(bpf_map_lookup_elem(map_fd, &key, &udp_cnt) == 0);
  83
  84                 key = IPPROTO_ICMP;
  85                 assert(bpf_map_lookup_elem(map_fd, &key, &icmp_cnt) == 0);
  86
  87                 printf("TCP %lld UDP %lld ICMP %lld packets\n",
  88                        tcp_cnt, udp_cnt, icmp_cnt);
  89                 sleep(1);
  90         }
  91
  92 cleanup:
  93         /* maps, programs, raw sockets will auto cleanup on process exit */
  94         return 0;
  95 }
  96
  97 int main(void)
  98 {
  99         FILE *f;
 100
 101         f = popen("ping -c5 localhost", "r");
 102         (void)f;
 103
 104         return test_sock();
 105 }