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
  31 char bpf_log_buf[BPF_LOG_BUF_SIZE];
  32
  33 static int test_sock(void)
  34 {
  35         int sock = -1, map_fd, prog_fd, i, key;
  36         long long value = 0, tcp_cnt, udp_cnt, icmp_cnt;
  37
  38         map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key), sizeof(value),
  39                                 256, 0);
  40         if (map_fd < 0) {
  41                 printf("failed to create map '%s'\n", strerror(errno));
  42                 goto cleanup;
  43         }
  44
  45         struct bpf_insn prog[] = {
  46                 BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
  47                 BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol) /* R0 = ip->proto */),
  48                 BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
  49                 BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
  50                 BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
  51                 BPF_LD_MAP_FD(BPF_REG_1, map_fd),
  52                 BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
  53                 BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
  54                 BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
  55                 BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
  56                 BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */
  57                 BPF_EXIT_INSN(),
  58         };
  59
  60         prog_fd = bpf_load_program(BPF_PROG_TYPE_SOCKET_FILTER, prog, sizeof(prog),
  61                                    "GPL", 0, bpf_log_buf, BPF_LOG_BUF_SIZE);
  62         if (prog_fd < 0) {
  63                 printf("failed to load prog '%s'\n", strerror(errno));
  64                 goto cleanup;
  65         }
  66
  67         sock = open_raw_sock("lo");
  68
  69         if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd,
  70                        sizeof(prog_fd)) < 0) {
  71                 printf("setsockopt %s\n", strerror(errno));
  72                 goto cleanup;
  73         }
  74
  75         for (i = 0; i < 10; i++) {
  76                 key = IPPROTO_TCP;
  77                 assert(bpf_map_lookup_elem(map_fd, &key, &tcp_cnt) == 0);
  78
  79                 key = IPPROTO_UDP;
  80                 assert(bpf_map_lookup_elem(map_fd, &key, &udp_cnt) == 0);
  81
  82                 key = IPPROTO_ICMP;
  83                 assert(bpf_map_lookup_elem(map_fd, &key, &icmp_cnt) == 0);
  84
  85                 printf("TCP %lld UDP %lld ICMP %lld packets\n",
  86                        tcp_cnt, udp_cnt, icmp_cnt);
  87                 sleep(1);
  88         }
  89
  90 cleanup:
  91         /* maps, programs, raw sockets will auto cleanup on process exit */
  92         return 0;
  93 }
  94
  95 int main(void)
  96 {
  97         FILE *f;
  98
  99         f = popen("ping -c5 localhost", "r");
 100         (void)f;
 101
 102         return test_sock();
 103 }