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