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netsniff.c
159 lines (131 loc) · 3.4 KB
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netsniff.c
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#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <pcap.h>
#include <arpa/inet.h>
#include "netsniff.h"
#define CAPTURE_INF -1
/* MAC + IP + TCP hdr */
#define MIN_SNAPLEN 54
#define err_exit(msg) do { \
fprintf(stderr, "%s", msg); \
exit(EXIT_FAILURE); \
} while (0)
static void
pkt_handler_en10mb(u_char *usr, const struct pcap_pkthdr *pkt,
const u_char *d);
static void
pkt_handler_linux_sll(u_char *usr, const struct pcap_pkthdr *pkt,
const u_char *d);
const char *
mac_str(char *__restrict buf, uint8_t *__restrict addr);
int main(int argc, char *argv[])
{
static struct program_options opts;
struct bpf_program fp;
char errbuff[PCAP_ERRBUF_SIZE];
pcap_t *pcap;
int err, linktype;
if (get_program_options(argc, argv, &opts))
err_exit("could not get program options\n");
if (!opts.interface)
opts.interface = "any";
if (opts.snaplen < MIN_SNAPLEN)
opts.snaplen = MIN_SNAPLEN;
pcap = pcap_open_live(opts.interface, opts.snaplen,
opts.promisc, 2000, errbuff);
if (!pcap)
err_exit("cannot open network interface\n");
err = pcap_compile(pcap, &fp, opts.bpf_expr, 0, -1);
if (err)
err_exit(pcap_geterr(pcap));
err = pcap_setfilter(pcap, &fp);
if (err)
err_exit(pcap_geterr(pcap));
linktype = pcap_datalink(pcap);
printf("datalink: %s\n", pcap_datalink_val_to_name(linktype));
switch (linktype) {
case DLT_EN10MB:
err = pcap_loop(pcap, CAPTURE_INF,
pkt_handler_en10mb, NULL);
break;
case DLT_LINUX_SLL:
err = pcap_loop(pcap, CAPTURE_INF,
pkt_handler_linux_sll, NULL);
break;
default:
err_exit("Datalink type is not yet supported!\n");
}
switch (err) {
case 0:
printf("netsniff terminated successfully\n");
break;
case -1:
case -2:
printf("netsniff terminated with error: %d\n", err);
break;
}
exit(EXIT_SUCCESS);
}
static char fmt_buf[1024];
static struct strbuf sb = {
.size = sizeof(fmt_buf),
.buf = fmt_buf,
};
static void etherframe_print(u_char *usr, const struct pcap_pkthdr *pkt,
const u_char *d, uint16_t ethtype)
{
struct iphdr *ip;
struct tcphdr *th;
struct udphdr *uh;
uint16_t ethtype_le;
ethtype_le = ntohs(ethtype);
switch (ethtype_le) {
case ETH_P_IP:
ip = ip_hdr(d);
sb_append_str(&sb, "IP: ");
iphdr_print(ip, &sb);
switch (ip->protocol) {
case IPPROTO_TCP:
th = tcp_hdr(d + ip_hdrlen(ip));
sb_append_str(&sb, "; TCP: ");
tcp_print(th, &sb);
break;
case IPPROTO_UDP:
uh = udp_hdr(d + ip_hdrlen(ip));
sb_append_str(&sb, "; UDP: ");
udp_print(uh, &sb);
break;
default:
sb_append_char(&sb, ' ');
sb_append_str(&sb, ipproto_str(ip->protocol));
}
break;
default:
/* FIXME: This code is open to buffer overrun errors */
sb_append_str(&sb, "ether type: ");
sb.len += sprintf(sb_curr(&sb), "0x%04x ", ethtype_le);
sb_append_str(&sb, ethertype_to_str(ethtype_le));
}
}
static void
pkt_handler_en10mb(u_char *usr, const struct pcap_pkthdr *pkt,
const u_char *d)
{
struct machdr *mac = mac_hdr(d);
sb_reset(&sb);
eth_print(mac, &sb);
sb_append_str(&sb, "; ");
etherframe_print(usr, pkt, d + ETH_HLEN, mac->type);
fprintf(stdout, "pkt: %s\n", sb.buf);
}
static void
pkt_handler_linux_sll(u_char *usr, const struct pcap_pkthdr *pkt,
const u_char *d)
{
struct dlt_linux_sll *ll = dlt_linux_sll_hdr(d);
BUILD_BUG_ON(sizeof(*ll) != 16);
sb_reset(&sb);
etherframe_print(usr, pkt, ll->payload, ll->proto_type);
fprintf(stdout, "pkt: %s\n", sb.buf);
}