Network interface scanner

iface_scan.c

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/if_packet.h>
#include <net/ethernet.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>


void print_addr(struct sockaddr *addr) {
    char *addr_string = malloc(sizeof(char) * 50);
    struct sockaddr_in *addr_in = (struct sockaddr_in *) addr;
    struct sockaddr_in6 *addr_in6 = (struct sockaddr_in6 *) addr;
    struct sockaddr_ll *addr_ll = (struct sockaddr_ll *) addr;
    int len = 0;

    // Casting for each address family (only for most common ones
    switch(addr->sa_family) {
        // IPv4
        case AF_INET:
            inet_ntop(addr_in->sin_family,
                    &addr_in->sin_addr, addr_string, 50);
            break;

        // IPv6
        case AF_INET6:
            inet_ntop(addr_in6->sin6_family,
                    &addr_in6->sin6_addr, addr_string, 50);
            break;

        // MAC address
        case AF_PACKET:
            len = 0;
            for(int i = 0; i < 6; i++)
                len += sprintf(addr_string + len, "%02X%s",
                        addr_ll->sll_addr[i], i < 5 ? ":":"");
            break;

        default:
            printf("Address family not supported\n");
            return;
    }


    if(addr_string == NULL) {
        printf("Couldn't find addresses related\n");
    } else {
        printf("%s\n", addr_string);
    }

    free(addr_string);
}


void print_iface(int niface, struct ifaddrs *nets_head){
    struct ifaddrs *next;

    // Iterate until selected structure
    next = nets_head;
    for(int i = 0; i < niface && next != NULL; i++)
        next = next->ifa_next;

    if(next == NULL) {
        printf("Couldn't find interface\n");
        return;
    }

    printf("=========================================================\n");

    printf("Name: %s\n", next->ifa_name);
    printf("Address: ");
    print_addr(next->ifa_addr);

    if(next->ifa_addr->sa_family == AF_INET ||
            next->ifa_addr->sa_family == AF_INET6) {
        printf("Netmask: ");
        print_addr(next->ifa_netmask);
    }

    printf("=========================================================\n");


}



int main(int argc, char *argv[]) {
    int ifchoice;
    struct ifaddrs *nets_head = malloc(sizeof(struct ifaddrs));
    struct ifaddrs *next; // aux variable to iterate through list
    getifaddrs(&nets_head);

    // List all net structures
    next = nets_head;
    for(int i = 0; next != NULL; i++) {
        printf("%d: %s\n", i, next->ifa_name);
        next = next->ifa_next;
    }

    // Choose structure to show details
    scanf("%d", &ifchoice);
    print_iface(ifchoice, nets_head);

    return 0;
}