/* Copyright (C) 2012-2015 P.D. Buchan (pdbuchan@yahoo.com) This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . */ // Send an IPv4 UDP packet via raw socket at the link layer (ethernet frame) // with a large payload requiring fragmentation. // Need to have destination MAC address. #include #include #include // close() #include // strcpy, memset(), and memcpy() #include // struct addrinfo #include // needed for socket(), uint8_t, uint16_t, uint32_t #include // needed for socket() #include // IPPROTO_UDP, INET_ADDRSTRLEN #include // struct ip and IP_MAXPACKET (which is 65535) #include // struct udphdr #include // inet_pton() and inet_ntop() #include // macro ioctl is defined #include // defines values for argument "request" of ioctl. #include // struct ifreq #include // ETH_P_IP = 0x0800, ETH_P_IPV6 = 0x86DD #include // struct sockaddr_ll (see man 7 packet) #include #include // errno, perror() // Define some constants. #define ETH_HDRLEN 14 // Ethernet header length #define IP4_HDRLEN 20 // IPv4 header length #define UDP_HDRLEN 8 // UDP header length, excludes data #define MAX_FRAGS 3120 // Maximum number of packet fragments (int) (65535 - UDP_HDRLEN) / (IP4_HDRLEN + 1 data byte)) // Function prototypes uint16_t checksum (uint16_t *, int); uint16_t udp4_checksum (struct ip, struct udphdr, uint8_t *, int); char *allocate_strmem (int); uint8_t *allocate_ustrmem (int); int *allocate_intmem (int); int main (int argc, char **argv) { int i, n, status, frame_length, sd, bytes; int *ip_flags, mtu, c, nframes, offset[MAX_FRAGS], len[MAX_FRAGS]; char *interface, *target, *src_ip, *dst_ip; struct ip iphdr; struct udphdr udphdr; int payloadlen, bufferlen; uint8_t *payload, *buffer, *src_mac, *dst_mac, *ether_frame; struct addrinfo hints, *res; struct sockaddr_in *ipv4; struct sockaddr_ll device; struct ifreq ifr; void *tmp; FILE *fi; // Allocate memory for various arrays. src_mac = allocate_ustrmem (6); dst_mac = allocate_ustrmem (6); payload = allocate_ustrmem (IP_MAXPACKET); ether_frame = allocate_ustrmem (IP_MAXPACKET); interface = allocate_strmem (40); target = allocate_strmem (40); src_ip = allocate_strmem (INET_ADDRSTRLEN); dst_ip = allocate_strmem (INET_ADDRSTRLEN); ip_flags = allocate_intmem (4); // Interface to send packet through. strcpy (interface, "eno1"); // Submit request for a socket descriptor to look up interface. if ((sd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) { perror ("socket() failed to get socket descriptor for using ioctl() "); exit (EXIT_FAILURE); } // Use ioctl() to get interface maximum transmission unit (MTU). memset (&ifr, 0, sizeof (ifr)); strcpy (ifr.ifr_name, interface); if (ioctl (sd, SIOCGIFMTU, &ifr) < 0) { perror ("ioctl() failed to get MTU "); return (EXIT_FAILURE); } mtu = ifr.ifr_mtu; printf ("Current MTU of interface %s is: %i\n", interface, mtu); // Use ioctl() to look up interface name and get its MAC address. memset (&ifr, 0, sizeof (ifr)); snprintf (ifr.ifr_name, sizeof (ifr.ifr_name), "%s", interface); if (ioctl (sd, SIOCGIFHWADDR, &ifr) < 0) { perror ("ioctl() failed to get source MAC address "); return (EXIT_FAILURE); } close (sd); // Copy source MAC address. memcpy (src_mac, ifr.ifr_hwaddr.sa_data, 6 * sizeof (uint8_t)); // Report source MAC address to stdout. printf ("MAC address for interface %s is ", interface); for (i=0; i<5; i++) { printf ("%02x:", src_mac[i]); } printf ("%02x\n", src_mac[5]); // Find interface index from interface name and store index in // struct sockaddr_ll device, which will be used as an argument of sendto(). memset (&device, 0, sizeof (device)); if ((device.sll_ifindex = if_nametoindex (interface)) == 0) { perror ("if_nametoindex() failed to obtain interface index "); exit (EXIT_FAILURE); } printf ("Index for interface %s is %i\n", interface, device.sll_ifindex); // Set destination MAC address: you need to fill these out dst_mac[0] = 0xff; dst_mac[1] = 0xff; dst_mac[2] = 0xff; dst_mac[3] = 0xff; dst_mac[4] = 0xff; dst_mac[5] = 0xff; // Source IPv4 address: you need to fill this out strcpy (src_ip, "192.168.0.240"); // Destination URL or IPv4 address strcpy (target, "www.google.com"); // Fill out hints for getaddrinfo(). memset (&hints, 0, sizeof (struct addrinfo)); hints.ai_family = AF_INET; hints.ai_socktype = SOCK_RAW; hints.ai_flags = hints.ai_flags | AI_CANONNAME; // Resolve target using getaddrinfo(). if ((status = getaddrinfo (target, NULL, &hints, &res)) != 0) { fprintf (stderr, "getaddrinfo() failed for target: %s\n", gai_strerror (status)); exit (EXIT_FAILURE); } ipv4 = (struct sockaddr_in *) res->ai_addr; tmp = &(ipv4->sin_addr); if (inet_ntop (AF_INET, tmp, dst_ip, INET_ADDRSTRLEN) == NULL) { status = errno; fprintf (stderr, "inet_ntop() failed for target.\nError message: %s", strerror (status)); exit (EXIT_FAILURE); } freeaddrinfo (res); // Fill out sockaddr_ll. device.sll_family = AF_PACKET; memcpy (device.sll_addr, src_mac, 6 * sizeof (uint8_t)); device.sll_halen = 6; // Get UDP data. i = 0; fi = fopen ("data", "r"); if (fi == NULL) { printf ("Can't open file 'data'.\n"); exit (EXIT_FAILURE); } while ((n=fgetc (fi)) != EOF) { payload[i] = n; i++; } fclose (fi); payloadlen = i; printf ("Upper layer protocol header length (bytes): %i\n", UDP_HDRLEN); printf ("Payload length (bytes): %i\n", payloadlen); // Length of fragmentable portion of packet. bufferlen = UDP_HDRLEN + payloadlen; printf ("Total fragmentable data (bytes): %i\n", bufferlen); // Allocate memory for a buffer for fragmentable portion. buffer = allocate_ustrmem (bufferlen); // Determine how many ethernet frames we'll need. memset (len, 0, MAX_FRAGS * sizeof (int)); memset (offset, 0, MAX_FRAGS * sizeof (int)); i = 0; c = 0; // Variable c is index to buffer, which contains upper layer protocol header and data. while (c < bufferlen) { // Do we still need to fragment remainder of fragmentable portion? if ((bufferlen - c)> (mtu - IP4_HDRLEN)) { // Yes len[i] = mtu - IP4_HDRLEN; // len[i] is amount of fragmentable part we can include in this frame. } else { // No len[i] = bufferlen - c; // len[i] is amount of fragmentable part we can include in this frame. } c += len[i]; // If not last fragment, make sure we have an even number of 8-byte blocks. // Reduce length as necessary. if (c < (bufferlen - 1)) { while ((len[i]%8)> 0) { len[i]--; c--; } } printf ("Frag: %i, Data (bytes): %i, Data Offset (8-byte blocks): %i\n", i, len[i], offset[i]); i++; offset[i] = (len[i-1] / 8) + offset[i-1]; } nframes = i; printf ("Total number of frames to send: %i\n", nframes); // IPv4 header // IPv4 header length (4 bits): Number of 32-bit words in header = 5 iphdr.ip_hl = IP4_HDRLEN / sizeof (uint32_t); // Internet Protocol version (4 bits): IPv4 iphdr.ip_v = 4; // Type of service (8 bits) iphdr.ip_tos = 0; // Total length of datagram (16 bits) // iphdr.ip_len is set for each fragment in loop below. // ID sequence number (16 bits) iphdr.ip_id = htons (31415); // Flags, and Fragmentation offset (3, 13 bits) // Zero (1 bit) ip_flags[0] = 0; // Do not fragment flag (1 bit) ip_flags[1] = 0; // More fragments following flag (1 bit) ip_flags[2] = 0; // Fragmentation offset (13 bits) ip_flags[3] = 0; iphdr.ip_off = htons ((ip_flags[0] << 15) + (ip_flags[1] << 14) + (ip_flags[2] << 13) + ip_flags[3]); // Time-to-Live (8 bits): default to maximum value iphdr.ip_ttl = 255; // Transport layer protocol (8 bits): 17 for UDP iphdr.ip_p = IPPROTO_UDP; // Source IPv4 address (32 bits) if ((status = inet_pton (AF_INET, src_ip, &(iphdr.ip_src))) != 1) { fprintf (stderr, "inet_pton() failed for source address.\nError message: %s", strerror (status)); exit (EXIT_FAILURE); } // Destination IPv4 address (32 bits) if ((status = inet_pton (AF_INET, dst_ip, &(iphdr.ip_dst))) != 1) { fprintf (stderr, "inet_pton() failed for destination address.\nError message: %s", strerror (status)); exit (EXIT_FAILURE); } // IPv4 header checksum (16 bits): set to 0 when calculating checksum iphdr.ip_sum = 0; iphdr.ip_sum = checksum ((uint16_t *) &iphdr, IP4_HDRLEN); // UDP header // Source port number (16 bits): pick a number udphdr.source = htons (4950); // Destination port number (16 bits): pick a number udphdr.dest = htons (4950); // Length of UDP datagram (16 bits): UDP header + UDP data udphdr.len = htons (UDP_HDRLEN + payloadlen); // UDP checksum (16 bits) udphdr.check = udp4_checksum (iphdr, udphdr, payload, payloadlen); // Build fragmentable portion of packet in buffer array. // UDP header memcpy (buffer, &udphdr, UDP_HDRLEN * sizeof (uint8_t)); // UDP data memcpy (buffer + UDP_HDRLEN, payload, payloadlen * sizeof (uint8_t)); // Submit request for a raw socket descriptor. if ((sd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) { perror ("socket() failed "); exit (EXIT_FAILURE); } // Loop through fragments. for (i=0; i 1) && (i < (nframes - 1))) { ip_flags[2] = 1u; } else { ip_flags[2] = 0u; } // Fragmentation offset (13 bits) ip_flags[3] = offset[i]; // Flags, and Fragmentation offset (3, 13 bits) iphdr.ip_off = htons ((ip_flags[0] << 15) + (ip_flags[1] << 14) + (ip_flags[2] << 13) + ip_flags[3]); // IPv4 header checksum (16 bits) iphdr.ip_sum = 0; iphdr.ip_sum = checksum ((uint16_t *) &iphdr, IP4_HDRLEN); // Copy IPv4 header to ethernet frame. memcpy (ether_frame + ETH_HDRLEN, &iphdr, IP4_HDRLEN * sizeof (uint8_t)); // Copy fragmentable portion of packet to ethernet frame. memcpy (ether_frame + ETH_HDRLEN + IP4_HDRLEN, buffer + (offset[i] * 8), len[i] * sizeof (uint8_t)); // Ethernet frame length = ethernet header (MAC + MAC + ethernet type) + ethernet data (IP header + fragment) frame_length = ETH_HDRLEN + IP4_HDRLEN + len[i]; // Send ethernet frame to socket. printf ("Sending fragment: %i\n", i); if ((bytes = sendto (sd, ether_frame, frame_length, 0, (struct sockaddr *) &device, sizeof (device))) <= 0) { perror ("sendto() failed"); exit (EXIT_FAILURE); } } // End loop nframes // Close socket descriptor. close (sd); // Free allocated memory. free (src_mac); free (dst_mac); free (ether_frame); free (interface); free (target); free (src_ip); free (dst_ip); free (ip_flags); free (payload); free (buffer); return (EXIT_SUCCESS); } // Computing the internet checksum (RFC 1071). // Note that the internet checksum is not guaranteed to preclude collisions. uint16_t checksum (uint16_t *addr, int len) { int count = len; register uint32_t sum = 0; uint16_t answer = 0; // Sum up 2-byte values until none or only one byte left. while (count> 1) { sum += *(addr++); count -= 2; } // Add left-over byte, if any. if (count> 0) { sum += *(uint8_t *) addr; } // Fold 32-bit sum into 16 bits; we lose information by doing this, // increasing the chances of a collision. // sum = (lower 16 bits) + (upper 16 bits shifted right 16 bits) while (sum>> 16) { sum = (sum & 0xffff) + (sum>> 16); } // Checksum is one's compliment of sum. answer = ~sum; return (answer); } // Build IPv4 UDP pseudo-header and call checksum function. uint16_t udp4_checksum (struct ip iphdr, struct udphdr udphdr, uint8_t *payload, int payloadlen) { char buf[IP_MAXPACKET]; char *ptr; int i, chksumlen = 0; memset (buf, 0, IP_MAXPACKET * sizeof (uint8_t)); ptr = &buf[0]; // ptr points to beginning of buffer buf // Copy source IP address into buf (32 bits) memcpy (ptr, &iphdr.ip_src.s_addr, sizeof (iphdr.ip_src.s_addr)); ptr += sizeof (iphdr.ip_src.s_addr); chksumlen += sizeof (iphdr.ip_src.s_addr); // Copy destination IP address into buf (32 bits) memcpy (ptr, &iphdr.ip_dst.s_addr, sizeof (iphdr.ip_dst.s_addr)); ptr += sizeof (iphdr.ip_dst.s_addr); chksumlen += sizeof (iphdr.ip_dst.s_addr); // Copy zero field to buf (8 bits) *ptr = 0; ptr++; chksumlen += 1; // Copy transport layer protocol to buf (8 bits) memcpy (ptr, &iphdr.ip_p, sizeof (iphdr.ip_p)); ptr += sizeof (iphdr.ip_p); chksumlen += sizeof (iphdr.ip_p); // Copy UDP length to buf (16 bits) memcpy (ptr, &udphdr.len, sizeof (udphdr.len)); ptr += sizeof (udphdr.len); chksumlen += sizeof (udphdr.len); // Copy UDP source port to buf (16 bits) memcpy (ptr, &udphdr.source, sizeof (udphdr.source)); ptr += sizeof (udphdr.source); chksumlen += sizeof (udphdr.source); // Copy UDP destination port to buf (16 bits) memcpy (ptr, &udphdr.dest, sizeof (udphdr.dest)); ptr += sizeof (udphdr.dest); chksumlen += sizeof (udphdr.dest); // Copy UDP length again to buf (16 bits) memcpy (ptr, &udphdr.len, sizeof (udphdr.len)); ptr += sizeof (udphdr.len); chksumlen += sizeof (udphdr.len); // Copy UDP checksum to buf (16 bits) // Zero, since we don't know it yet *ptr = 0; ptr++; *ptr = 0; ptr++; chksumlen += 2; // Copy payload to buf memcpy (ptr, payload, payloadlen); ptr += payloadlen; chksumlen += payloadlen; // Pad to the next 16-bit boundary i = 0; while (((payloadlen+i)%2) != 0) { i++; chksumlen++; ptr++; } return checksum ((uint16_t *) buf, chksumlen); } // Allocate memory for an array of chars. char * allocate_strmem (int len) { void *tmp; if (len <= 0) { fprintf (stderr, "ERROR: Cannot allocate memory because len = %i in allocate_strmem().\n", len); exit (EXIT_FAILURE); } tmp = (char *) malloc (len * sizeof (char)); if (tmp != NULL) { memset (tmp, 0, len * sizeof (char)); return (tmp); } else { fprintf (stderr, "ERROR: Cannot allocate memory for array allocate_strmem().\n"); exit (EXIT_FAILURE); } } // Allocate memory for an array of unsigned chars. uint8_t * allocate_ustrmem (int len) { void *tmp; if (len <= 0) { fprintf (stderr, "ERROR: Cannot allocate memory because len = %i in allocate_ustrmem().\n", len); exit (EXIT_FAILURE); } tmp = (uint8_t *) malloc (len * sizeof (uint8_t)); if (tmp != NULL) { memset (tmp, 0, len * sizeof (uint8_t)); return (tmp); } else { fprintf (stderr, "ERROR: Cannot allocate memory for array allocate_ustrmem().\n"); exit (EXIT_FAILURE); } } // Allocate memory for an array of ints. int * allocate_intmem (int len) { void *tmp; if (len <= 0) { fprintf (stderr, "ERROR: Cannot allocate memory because len = %i in allocate_intmem().\n", len); exit (EXIT_FAILURE); } tmp = (int *) malloc (len * sizeof (int)); if (tmp != NULL) { memset (tmp, 0, len * sizeof (int)); return (tmp); } else { fprintf (stderr, "ERROR: Cannot allocate memory for array allocate_intmem().\n"); exit (EXIT_FAILURE); } }

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