cregit-Linux how code gets into the kernel

Release 4.7 samples/bpf/sock_example.c

Directory: samples/bpf
/* eBPF example program:
 * - creates arraymap in kernel with key 4 bytes and value 8 bytes
 *
 * - loads eBPF program:
 *   r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)];
 *   *(u32*)(fp - 4) = r0;
 *   // assuming packet is IPv4, lookup ip->proto in a map
 *   value = bpf_map_lookup_elem(map_fd, fp - 4);
 *   if (value)
 *        (*(u64*)value) += 1;
 *
 * - attaches this program to eth0 raw socket
 *
 * - every second user space reads map[tcp], map[udp], map[icmp] to see
 *   how many packets of given protocol were seen on eth0
 */
#include <stdio.h>
#include <unistd.h>
#include <assert.h>
#include <linux/bpf.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <stddef.h>
#include "libbpf.h"


static int test_sock(void) { int sock = -1, map_fd, prog_fd, i, key; long long value = 0, tcp_cnt, udp_cnt, icmp_cnt; map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key), sizeof(value), 256, 0); if (map_fd < 0) { printf("failed to create map '%s'\n", strerror(errno)); goto cleanup; } struct bpf_insn prog[] = { BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol) /* R0 = ip->proto */), BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */ BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */ BPF_LD_MAP_FD(BPF_REG_1, map_fd), BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2), BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */ BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */ BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */ BPF_EXIT_INSN(), }; prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog, sizeof(prog), "GPL", 0); if (prog_fd < 0) { printf("failed to load prog '%s'\n", strerror(errno)); goto cleanup; } sock = open_raw_sock("lo"); if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd, sizeof(prog_fd)) < 0) { printf("setsockopt %s\n", strerror(errno)); goto cleanup; } for (i = 0; i < 10; i++) { key = IPPROTO_TCP; assert(bpf_lookup_elem(map_fd, &key, &tcp_cnt) == 0); key = IPPROTO_UDP; assert(bpf_lookup_elem(map_fd, &key, &udp_cnt) == 0); key = IPPROTO_ICMP; assert(bpf_lookup_elem(map_fd, &key, &icmp_cnt) == 0); printf("TCP %lld UDP %lld ICMP %lld packets\n", tcp_cnt, udp_cnt, icmp_cnt); sleep(1); } cleanup: /* maps, programs, raw sockets will auto cleanup on process exit */ return 0; }

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int main(void) { FILE *f; f = popen("ping -c5 localhost", "r"); (void)f; return test_sock(); }

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Directory: samples/bpf
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