67 lines
1.6 KiB
C
67 lines
1.6 KiB
C
#include <arpa/inet.h>
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#include <err.h>
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#include <errno.h>
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#include <linux/if_packet.h>
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#include <net/ethernet.h>
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#include <net/if.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <string.h>
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#include <sys/ioctl.h>
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#include <sys/socket.h>
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#include <sys/types.h>
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#include <unistd.h>
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int main(void) {
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// Create a packet socket
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errno = 0;
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int packet_socket = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
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if (packet_socket == -1) {
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err(1, "socket");
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}
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// Find the index of the network interface
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struct ifreq ifr;
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strncpy(ifr.ifr_name, "wlan0", IFNAMSIZ);
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errno = 0;
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if (ioctl(packet_socket, SIOCGIFINDEX, &ifr) == -1) {
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err(1, "ioctl");
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}
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// Bind to the network interface
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struct sockaddr_ll sll;
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sll.sll_family = AF_PACKET;
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sll.sll_protocol = htons(ETH_P_ALL);
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sll.sll_ifindex = ifr.ifr_ifindex;
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errno = 0;
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if (bind(packet_socket, (const struct sockaddr*)&sll, sizeof(sll)) == -1) {
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err(1, "bind");
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}
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for(;;) {
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char frame[1522]; // 1522 is the largest a 802.3 frame can be
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errno = 0;
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ssize_t frame_length = recv(packet_socket, frame, sizeof(frame), MSG_TRUNC);
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if (frame_length == -1) {
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err(1, "recv");
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}
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// Extract EtherType / length field
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// 012345 012345 01
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// dest source ^^
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// It is stored in the network byte order, that is, high byte 1st
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if (frame_length < 14) {
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errx(1, "Very weird frame of only %zdB???", frame_length);
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}
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uint16_t ethertype_length = (frame[12] << 8) | frame[13];
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errno = 0;
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if(printf("ethertype: %02x%02x, length: %zd\n", ethertype_length >> 8, ethertype_length & 0xff, frame_length) == -1) {
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err(1, "printf");
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}
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}
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return 0;
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}
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