The following is a program that captures TCP packets < port 80 > and prints header related information in the console for every packet. I have also included a timer , so that after every 1000 millisec i.e. 1 sec , the frequency of occurence of various flags , and distinct number of Src IPs , Ack nos and Seq nos encountered are written into a file. I’m working in fedora core 5. I am encountering the following problems :
1.file writing part works fine during some executions , but most of the other times ,in the same machine , the file is not at all written to.
2.When i execute this program in my house , about 30 packets are captured every second. But when i run the same program in my lab , just 1 packet is captured per second. ( though i do the same amount of browsing in both places )
#define INTERVAL 1000 /* number of milliseconds to go off */
#include <pcap.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/time.h> // for setitimer
#include<unistd.h> // for pause
#include <signal.h> /* for signal */
/* default snap length (maximum bytes per packet to capture) */
#define SNAP_LEN 1518
/* ethernet headers are always exactly 14 bytes [1] */
#define SIZE_ETHERNET 14
/* Ethernet addresses are 6 bytes */
#define ETHER_ADDR_LEN 6
/* Ethernet header */
struct sniff_ethernet {
u_char ether_dhost[ETHER_ADDR_LEN]; /* destination host address */
u_char ether_shost[ETHER_ADDR_LEN]; /* source host address */
u_short ether_type; /* IP? ARP? RARP? etc */
};
/* IP header */
struct sniff_ip {
u_char ip_vhl; /* version << 4 | header length >> 2 */
u_char ip_tos; /* type of service */
u_short ip_len; /* total length */
u_short ip_id; /* identification */
u_short ip_off; /* fragment offset field */
#define IP_RF 0x8000 /* reserved fragment flag */
#define IP_DF 0x4000 /* dont fragment flag */
#define IP_MF 0x2000 /* more fragments flag */
#define IP_OFFMASK 0x1fff /* mask for fragmenting bits */
u_char ip_ttl; /* time to live */
u_char ip_p; /* protocol */
u_short ip_sum; /* checksum */
struct in_addr ip_src,ip_dst; /* source and dest address */
};
#define IP_HL(ip) (((ip)->ip_vhl) & 0x0f)
#define IP_V(ip) (((ip)->ip_vhl) >> 4)
/* TCP header */
typedef u_int tcp_seq;
struct sniff_tcp {
u_short th_sport; /* source port */
u_short th_dport; /* destination port */
tcp_seq th_seq; /* sequence number */
tcp_seq th_ack; /* acknowledgement number */
u_char th_offx2; /* data offset, rsvd */
#define TH_OFF(th) (((th)->th_offx2 & 0xf0) >> 4)
u_char th_flags;
#define TH_FIN 0x01
#define TH_SYN 0x02
#define TH_RST 0x04
#define TH_PUSH 0x08
#define TH_ACK 0x10
#define TH_URG 0x20
#define TH_ECE 0x40
#define TH_CWR 0x80
#define TH_FLAGS (TH_FIN|TH_SYN|TH_RST|TH_ACK|TH_URG|TH_ECE|TH_CWR)
u_short th_win; /* window */
u_short th_sum; /* checksum */
u_short th_urp; /* urgent pointer */
};
u_short sport[100];int spd=0;
u_int seq[100];int seqd=0;
u_short win[100];int wind=0;
FILE* urlfile;
int count = 1,flag=0,t=0;
float sc=0,ac=0,fc=0,pc=0,uc=0,rc=0;
void
got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet);
void
print_payload(const u_char *payload, int len);
void
print_hex_ascii_line(const u_char *payload, int len, int offset);
void
print_app_usage(void);
void DoStuff(void);
void DoStuff(void) {
t++;
printf("Timer %d went off.########################################\n",t);
// fprintf(urlfile,"\n hi hi");
fprintf(urlfile,"\ntime %d 1:%f 2:%f 3:%f 4:%f 5:%f 6:%f 7:%f 8:%f 9:%f",t,sc/count,ac/count,fc/count,pc/count,uc/count,rc/count,(float)spd/count,(float)wind/count,(float)seqd/count);
printf("\ntime %d 1:%f 2:%f 3:%f 4:%f 5:%f 6:%f 7:%f 8:%f 9:%f",t,sc/count,ac/count,fc/count,pc/count,uc/count,rc/count,(float)spd/count,(float)wind/count,(float)seqd/count);
printf("\n a_count : %f , total_packets : %d , frequency : %f",ac,count,ac/count);
printf("\n r_count : %f , total_packets : %d , frequency : %f",rc,count,rc/count);
printf("\n p_count : %f , total_packets : %d , frequency : %f",pc,count,pc/count);
printf("\n s_count : %f , total_packets : %d , frequency : %f",sc,count,sc/count);
printf("\n u_count : %f , total_packets : %d , frequency : %f",uc,count,uc/count);
printf("\n f_count : %f , total_packets : %d , frequency : %f",fc,count,fc/count);
printf("\ncount of distinct seq nos : %d no/pcount : %f ",seqd,(float)seqd/count);
printf("\ncount of distinct sports : %d no/pcount : %f ",spd,(float)spd/count);
printf("\ncount of distinct win nos : %d no/pcount : %f\n\n ",wind,(float)wind/count);
ac=rc=pc=fc=sc=uc=0;count=1;
spd=seqd=wind=0;
}
void
print_app_usage(void)
{
printf("Usage: ./a.out [interface]\n");
printf("\n");
printf("Options:\n");
printf(" interface Listen on <interface> for packets.\n");
printf("\n");
return;
}
/*
* dissect/print packet
*/
void
got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet)
{
/* packet counter */
int j;
/* declare pointers to packet headers */
const struct sniff_ethernet *ethernet; /* The ethernet header [1] */
const struct sniff_ip *ip; /* The IP header */
const struct sniff_tcp *tcp; /* The TCP header */
const char *payload; /* Packet payload */
int size_ip;
int size_tcp;
int size_payload;
printf("\nPacket number %d:\n", count);
count++;
/* define ethernet header */
ethernet = (struct sniff_ethernet*)(packet);
/* define/compute ip header offset */
ip = (struct sniff_ip*)(packet + SIZE_ETHERNET);
size_ip = IP_HL(ip)*4;
if (size_ip < 20) {
printf(" * Invalid IP header length: %u bytes\n", size_ip);
return;
}
switch(ip->ip_p) {
case IPPROTO_TCP:
printf(" Protocol: TCP\n");
break;
case IPPROTO_UDP:
printf(" Protocol: UDP\n");
return;
case IPPROTO_ICMP:
printf(" Protocol: ICMP\n");
return;
case IPPROTO_IP:
printf(" Protocol: IP\n");
return;
default:
printf(" Protocol: unknown\n");
return;
}
/* define/compute tcp header offset */
tcp = (struct sniff_tcp*)(packet + SIZE_ETHERNET + size_ip);
size_tcp = TH_OFF(tcp)*4;
if (size_tcp < 20) {
printf(" * Invalid TCP header length: %u bytes\n", size_tcp);
return;
}
flag=0;
for(j=0;j<spd;j++)
{
if(sport[j]==ntohs(tcp->th_sport)) { flag=1; break; }
}
if(flag==0) sport[spd++]=ntohs(tcp->th_sport);
flag=0;
for(j=0;j<seqd;j++)
{
if(seq[j]==ntohs(tcp->th_seq)) { flag=1; break; }
}
if(flag==0) seq[seqd++]=ntohs(tcp->th_seq);
flag=0;
for(j=0;j<wind;j++)
{
if(win[j]==ntohs(tcp->th_win)) { flag=1; break; }
}
if(flag==0) win[wind++]=ntohs(tcp->th_win);
printf(" Src port: %d\n", ntohs(tcp->th_sport));
printf(" Window: %d\n", ntohs(tcp->th_win));
printf(" Sequence no: %d\n", ntohs(tcp->th_seq));
if (tcp->th_flags & TH_URG){
printf(" Flag: TH_URG");uc++;
}
if (tcp->th_flags & TH_RST){
printf(" Flag: TH_RST");rc++;
}
if (tcp->th_flags & TH_ACK){
printf(" Flag: TH_ACK");ac++;
}
if (tcp->th_flags & TH_PUSH){
printf(" Flag: TH_PUSH");pc++;
}
if (tcp->th_flags & TH_SYN){
printf(" Flag: TH_SYN");sc++;
}
if (tcp->th_flags & TH_FIN){
printf(" Flag: TH_FIN");fc++;
}
if (size_payload > 0) {
printf(" Payload (%d bytes):\n", size_payload);
}
return;
}
int main(int argc, char **argv)
{
char *dev = NULL; /* capture device name */
char errbuf[PCAP_ERRBUF_SIZE]; /* error buffer */
pcap_t *handle; /* packet capture handle */
char filter_exp[] = "tcp port 80";
struct bpf_program fp; /* compiled filter program (expression) */
bpf_u_int32 mask; /* subnet mask */
bpf_u_int32 net; /* ip */
//int num_packets = 10; /* number of packets to capture */
/* check for capture device name on command-line */
if (argc == 2) {
dev = argv[1];
}
else if (argc > 2) {
fprintf(stderr, "error: unrecognized command-line options\n\n");
print_app_usage();
exit(EXIT_FAILURE);
}
else {
/* find a capture device if not specified on command-line */
dev = pcap_lookupdev(errbuf);
if (dev == NULL) {
fprintf(stderr, "Couldn't find default device: %s\n",
errbuf);
exit(EXIT_FAILURE);
}
}
/* get network number and mask associated with capture device */
if (pcap_lookupnet(dev, &net, &mask, errbuf) == -1) {
fprintf(stderr, "Couldn't get netmask for device %s: %s\n",
dev, errbuf);
net = 0;
mask = 0;
}
/* print capture info */
printf("Device: %s\n", dev);
printf("Filter expression: %s\n", filter_exp);
/* open capture device */
handle = pcap_open_live(dev, SNAP_LEN, 1, 1000, errbuf);
if (handle == NULL) {
fprintf(stderr, "Couldn't open device %s: %s\n", dev, errbuf);
exit(EXIT_FAILURE);
}
/* make sure we're capturing on an Ethernet device [2] */
if (pcap_datalink(handle) != DLT_EN10MB) {
fprintf(stderr, "%s is not an Ethernet\n", dev);
exit(EXIT_FAILURE);
}
/* compile the filter expression */
if (pcap_compile(handle, &fp, filter_exp, 0, net) == -1) {
fprintf(stderr, "Couldn't parse filter %s: %s\n",
filter_exp, pcap_geterr(handle));
exit(EXIT_FAILURE);
}
/* apply the compiled filter */
if (pcap_setfilter(handle, &fp) == -1) {
fprintf(stderr, "Couldn't install filter %s: %s\n",
filter_exp, pcap_geterr(handle));
exit(EXIT_FAILURE);
}
urlfile=fopen("output.txt","w");
if(urlfile==NULL) printf("Unable to create file.");
// timer code
struct itimerval it_val; /* for setting itimer */
/* Upon SIGALRM, call DoStuff().
* Set interval timer. We want frequency in ms,
* but the setitimer call needs seconds and useconds. */
if (signal(SIGALRM, (void (*)(int)) DoStuff) == SIG_ERR) {
perror("Unable to catch SIGALRM");
exit(1);
}
it_val.it_value.tv_sec = INTERVAL/1000;
it_val.it_value.tv_usec = (INTERVAL*1000) % 1000000;
it_val.it_interval = it_val.it_value;
if (setitimer(ITIMER_REAL, &it_val, NULL) == -1) {
perror("error calling setitimer()");
exit(1);
}
/* now we can set our callback function */
//pcap_loop(handle, num_packets, got_packet, NULL);
pcap_loop(handle,-1, got_packet, NULL);// set num_packets to -1 to capture indefinitely.
/* cleanup */
pcap_freecode(&fp);
pcap_close(handle);
fclose(urlfile);
printf("\nCapture complete.\n");
return 0;
}
As this is a part of my project , i’m right now stuck at this point.. Can anyone please suggest regarding what may have gone wrong.. Thanks in advance.
Have you tried
fflush()?