pcapmirror/main.c

/*
pcapmirror - A simple packet mirroring tool using libpcap

Copyright (c) 2025, Matthias Cramer, cramer@freestone.net
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <pcap.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip6.h>
#include <net/if_arp.h>
#include <netinet/if_ether.h> // For Ethernet and ARP headers
#include <arpa/inet.h>
#include <netdb.h>

#define DEFAULT_DEST_PORT 37008 // Default TZSP port
#define TZSP_ENCAP_LEN 4       // Length of TZSP encapsulation header
#define TZSP_TAGGED_LEN 1      // Length of TZSP tagged field header (type)
#define ETHERNET_HEADER_LENGTH 14 // Assuming Ethernet header is 14 bytes

// TZSP Header Structure
struct tzsp_header {
    unsigned char version;      // Version (usually 1 or 2)
    unsigned char type;         // Type (0x01 for packet)
    unsigned short encapsulated_protocol; // Encapsulated protocol (Ethernet = 1)
    unsigned short length;      // Length of the payload + header
};

// TZSP Tagged Field Structure
struct tzsp_tagged {
    unsigned char type;         // Tag type
};

// Add this structure for ARP header parsing
struct arp_header {
    uint16_t htype;    // Hardware type
    uint16_t ptype;    // Protocol type
    uint8_t hlen;      // Hardware address length
    uint8_t plen;      // Protocol address length
    uint16_t oper;     // Operation (1 = request, 2 = reply)
    uint8_t sha[6];    // Sender hardware address
    uint8_t spa[4];    // Sender protocol address
    uint8_t tha[6];    // Target hardware address
    uint8_t tpa[4];    // Target protocol address
};

// Function to check if the system is little-endian
int is_little_endian() {
    volatile unsigned int i=0x01234567;
    return (((unsigned char*)&i)[0] == 0x67);
}

void list_interfaces() {
    pcap_if_t *alldevs;
    char errbuf[PCAP_ERRBUF_SIZE];
    if (pcap_findalldevs(&alldevs, errbuf) == -1) {
        fprintf(stderr, "Error in pcap_findalldevs: %s\n", errbuf);
        return;
    }
    printf("Available network interfaces:\n");
    for (pcap_if_t *d = alldevs; d != NULL; d = d->next) {
        printf("%s", d->name);
        if (d->description) {
            printf(" (%s)", d->description);
        }
        printf("\n");
    }
    pcap_freealldevs(alldevs);
}

void print_usage(const char *program_name) {
    printf("Usage: %s [options]\n", program_name);
    printf("Options:\n");
    printf("  -i <interface>       Specify the capture interface\n");
    printf("  -f <filter>          Specify the capture filter (BPF syntax)\n");
    printf("  -r <host/ipv4/ipv6>  Specify the destination host (required)\n");
    printf("  -p <port>            Specify the destination port (default: %d)\n", DEFAULT_DEST_PORT);
    printf("  -4                   Force IPv4 host lookup\n");
    printf("  -6                   Force IPv6 host lookup\n");
    printf("  -l                   List available network interfaces\n");
    printf("  -v                   Enable verbose mode\n");
    printf("  -h                   Show this help message\n");
    printf("Example:\n");
    printf("  %s -i eth0 -f 'tcp port 80' -v -r 192.168.1.100 -p 47008\n", program_name);
}

int main(int argc, char *argv[]) {
    char errbuf[PCAP_ERRBUF_SIZE];
    char *filter_exp = ""; // Default filter
    char *dev_name = NULL; // Device name
    char *mirror_host = NULL; // Destination IP, no default value
    int dest_port = DEFAULT_DEST_PORT; // Destination port, default value
    int i;
    int verbose = 0; // Verbose flag, default is false
    int force_ipv4 = 0; // Flag to force IPv4 lookup
    int force_ipv6 = 0; // Flag to force IPv6 lookup
    int list_interfaces_flag = 0; // Flag to list interfaces

    // Socket variables
    int sockfd;
    struct addrinfo hints, *res;
    struct sockaddr_storage dest_addr; // Declare dest_addr
    int dest_addr_size;

    // Check if no arguments are given or if help is requested
    if (argc == 1 || (argc == 2 && strcmp(argv[1], "-h") == 0)) {
        print_usage(argv[0]);
        return 0;
    }

    // Parse command-line arguments
    for (i = 1; i < argc; i++) {
        if (strcmp(argv[i], "-f") == 0 && i + 1 < argc) {
            filter_exp = argv[i + 1];
            i++; // Skip the filter value
        } else if (strcmp(argv[i], "-i") == 0 && i + 1 < argc) {
            dev_name = argv[i + 1];
            i++; // Skip the interface value
        } else if (strcmp(argv[i], "-v") == 0) {
            verbose = 1; // Enable verbose mode
        } else if (strcmp(argv[i], "-h") == 0) {
            print_usage(argv[0]);
            return 0;
        } else if (strcmp(argv[i], "-r") == 0 && i + 1 < argc) {
            mirror_host = argv[i + 1]; // Set destination IP from command line
            i++; // Skip the IP value
        } else if (strcmp(argv[i], "-p") == 0 && i + 1 < argc) {
            dest_port = atoi(argv[i + 1]); // Set destination port from command line
            i++; // Skip the port value
        } else if (strcmp(argv[i], "-4") == 0) {
            force_ipv4 = 1; // Force IPv4 lookup
        } else if (strcmp(argv[i], "-6") == 0) {
            force_ipv6 = 1; // Force IPv6 lookup
        } else if (strcmp(argv[i], "-l") == 0) {
            list_interfaces_flag = 1; // Set flag to list interfaces
        }
    }

    if (list_interfaces_flag) {
        list_interfaces();
        return 0;
    }

    // Check if destination IP is provided
    if (mirror_host == NULL && !list_interfaces_flag) {
        fprintf(stderr, "Error: Destination IP address is required.\n");
        print_usage(argv[0]);
        return 1;
    }

    // Check that interface is not any
    if (dev_name != NULL && strcmp(dev_name, "any") == 0) {
        fprintf(stderr, "Error: Interface 'any' is not supported.\n");
        return 1;
    }

    // Resolve the destination address
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_UNSPEC; // Allow IPv4 or IPv6
    hints.ai_socktype = SOCK_DGRAM; // Datagram socket

    if (force_ipv4) {
        hints.ai_family = AF_INET; // Force IPv4
    } else if (force_ipv6) {
        hints.ai_family = AF_INET6; // Force IPv6
    }

    if (getaddrinfo(mirror_host, NULL, &hints, &res) != 0) {
        perror("getaddrinfo");
        return 1;
    }

    // Calculate dest_addr size
    if (res->ai_family == AF_INET) {
        dest_addr_size = sizeof(struct sockaddr_in);
    } else if (res->ai_family == AF_INET6) {
        dest_addr_size = sizeof(struct sockaddr_in6);
    } else {
        fprintf(stderr, "Unknown address family\n");
        freeaddrinfo(res);
        return 1;
    }

    // Create UDP socket
    sockfd = socket(res->ai_family, SOCK_DGRAM, 0);
    if (sockfd == -1) {
        perror("socket");
        freeaddrinfo(res);
        return 1;
    }

    memset(&dest_addr, 0, sizeof(dest_addr));

    // Set the destination address
    if (res->ai_family == AF_INET) {
        struct sockaddr_in *ipv4 = (struct sockaddr_in *)res->ai_addr;
        ipv4->sin_port = htons(dest_port);
        memcpy(&dest_addr, ipv4, sizeof(struct sockaddr_in));
    } else if (res->ai_family == AF_INET6) {
        struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)res->ai_addr;
        ipv6->sin6_port = htons(dest_port);
        memcpy(&dest_addr, ipv6, sizeof(struct sockaddr_in6));
    }

    // Resolve the destination IP address
    char resolved_ip[INET6_ADDRSTRLEN];
    if (res->ai_family == AF_INET) {
        struct sockaddr_in *ipv4 = (struct sockaddr_in *)res->ai_addr;
        inet_ntop(AF_INET, &(ipv4->sin_addr), resolved_ip, INET6_ADDRSTRLEN);
    } else if (res->ai_family == AF_INET6) {
        struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)res->ai_addr;
        inet_ntop(AF_INET6, &(ipv6->sin6_addr), resolved_ip, INET6_ADDRSTRLEN);
    }

    // Free the address info
    freeaddrinfo(res);

    printf("Using interface: %s\n", dev_name);
    printf("Using filter: %s\n", filter_exp);
    printf("Resolved Destination IP: %s\n", resolved_ip);
    printf("Destination Port: %d\n", dest_port);

    pcap_t *handle;
    struct bpf_program fp;
    bpf_u_int32 mask;
    bpf_u_int32 net;

    if (pcap_lookupnet(dev_name, &net, &mask, errbuf) == -1) {
        fprintf(stderr, "Can't get netmask for device %s: %s\n", dev_name, errbuf);
        net = 0;
        mask = 0;
    }

    handle = pcap_open_live(dev_name, BUFSIZ, 1, 1000, errbuf);
    if (handle == NULL) {
        fprintf(stderr, "Couldn't open device %s: %s\n", dev_name, errbuf);
        return(2);
    }

    if (pcap_compile(handle, &fp, filter_exp, 1, net) == -1) {
        fprintf(stderr, "Couldn't parse filter %s: %s\n", filter_exp, pcap_geterr(handle));
        pcap_close(handle);
        return(2);
    }

    if (pcap_setfilter(handle, &fp) == -1) {
        fprintf(stderr, "Couldn't install filter %s: %s\n", filter_exp, pcap_geterr(handle));
        pcap_close(handle);
        return(2);
    }

    struct pcap_pkthdr header;
    const u_char *packet;
    char source_ip_str[INET6_ADDRSTRLEN], dest_ip_str[INET6_ADDRSTRLEN];
    struct ip *ip_header; // Declare ip4_header
    struct ip6_hdr *ip6_header; // Declare ip6_header
    int ip_protocol = 0;

    while (1) {
        packet = pcap_next(handle, &header);
        if (packet == NULL)
            continue;

        if (verbose) {

            // Parse Ethernet header
            struct ether_header *eth_header = (struct ether_header *)packet;

            // Check EtherType
            uint16_t ether_type = ntohs(eth_header->ether_type);

            if (ether_type == ETHERTYPE_IP) {
                // Handle IPv4 traffic
                ip_header = (struct ip *)(packet + ETHERNET_HEADER_LENGTH);
                ip_protocol = ip_header->ip_v & 0x0F; // Get IP version
        
                if (ip_protocol == 4) {
                    inet_ntop(AF_INET, &(ip_header->ip_src.s_addr), source_ip_str, INET6_ADDRSTRLEN);
                    inet_ntop(AF_INET, &(ip_header->ip_dst.s_addr), dest_ip_str, INET6_ADDRSTRLEN);
        
                    printf("IPv4 Packet: %s -> %s, IP Protocol: %d\n",
                           source_ip_str, dest_ip_str, ip_header->ip_p);
                }
            } else if (ether_type == ETHERTYPE_IPV6) {
                // Handle IPv6 traffic
                ip6_header = (struct ip6_hdr *)(packet + ETHERNET_HEADER_LENGTH);
                inet_ntop(AF_INET6, &(ip6_header->ip6_src), source_ip_str, INET6_ADDRSTRLEN);
                inet_ntop(AF_INET6, &(ip6_header->ip6_dst), dest_ip_str, INET6_ADDRSTRLEN);
        
                printf("IPv6 Packet: %s -> %s, Next Header: %d\n",
                       source_ip_str, dest_ip_str, ip6_header->ip6_nxt);
            } else if (ether_type == ETHERTYPE_ARP) {
                // Handle ARP traffic
                struct arp_header *arp = (struct arp_header *)(packet + ETHERNET_HEADER_LENGTH);
        
                printf("ARP Packet: Operation: %s\n",
                       (ntohs(arp->oper) == 1) ? "Request" : "Reply");
                printf("Sender MAC: %02x:%02x:%02x:%02x:%02x:%02x, Sender IP: %d.%d.%d.%d\n",
                       arp->sha[0], arp->sha[1], arp->sha[2], arp->sha[3], arp->sha[4], arp->sha[5],
                       arp->spa[0], arp->spa[1], arp->spa[2], arp->spa[3]);
                printf("Target MAC: %02x:%02x:%02x:%02x:%02x:%02x, Target IP: %d.%d.%d.%d\n",
                       arp->tha[0], arp->tha[1], arp->tha[2], arp->tha[3], arp->tha[4], arp->tha[5],
                       arp->tpa[0], arp->tpa[1], arp->tpa[2], arp->tpa[3]);
            } else {
                printf("Non-IP/ARP Packet, EtherType: 0x%04x\n", ether_type);
            }
        }

        // Create TZSP Header
        struct tzsp_header tzsp;
        tzsp.version = 1;          // TZSP Version 1
        tzsp.type = 1;          // Type 1 for packet
        tzsp.encapsulated_protocol = htons(1); // Ethernet

        // Create TZSP Tagged Field for End of Fields
        struct tzsp_tagged end_tag;
        end_tag.type = 1;             // End of Fields

        // Calculate total length
        unsigned short total_length = header.caplen + TZSP_ENCAP_LEN + TZSP_TAGGED_LEN;
        tzsp.length = htons(total_length);

        // Allocate memory for TZSP packet
        unsigned char *tzsp_packet = (unsigned char *)malloc(total_length);
        if (tzsp_packet == NULL) {
            perror("malloc");
            continue; // Skip this packet
        }

        // Copy TZSP header and tagged field and packet data into the new buffer
        unsigned char *ptr = tzsp_packet;
        memcpy(ptr, &tzsp, TZSP_ENCAP_LEN);
        ptr += TZSP_ENCAP_LEN;
        memcpy(ptr, &end_tag, TZSP_TAGGED_LEN);
        ptr += TZSP_TAGGED_LEN;
        memcpy(ptr, packet, header.caplen);

        // Send packet via UDP with TZSP encapsulation
        if (sendto(sockfd, tzsp_packet, total_length, 0, (struct sockaddr *)&dest_addr, dest_addr_size) == -1) {
            perror("sendto");
        }

        free(tzsp_packet); // Free allocated memory
    }

    pcap_freecode(&fp);
    pcap_close(handle);
    close(sockfd);
    return(0);
}