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(转载)Linux操作系统Ubuntu下GCC之libpcap库基本代码

2014年03月14日 ⁄ 综合 ⁄ 共 16368字 ⁄ 字号 评论关闭

 

/*
 * sniffex.c
 *
 * Sniffer example of TCP/IP packet capture using libpcap.
 *
 * Version 0.1.1 (2005-07-05)
 * Copyright (c) 2005 The Tcpdump Group
 *
 * This software is intended to be used as a practical example and
 * demonstration of the libpcap library; available at:
 * http://www.tcpdump.org/
 *
 ****************************************************************************
 *
 * This software is a modification of Tim Carstens' "sniffer.c"
 * demonstration source code, released as follows:
 *
 * sniffer.c
 * Copyright (c) 2002 Tim Carstens
 * 2002-01-07
 * Demonstration of using libpcap
 * timcarst -at- yahoo -dot- com
 *
 * "sniffer.c" is distributed under these terms:
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. The name "Tim Carstens" may not be used to endorse or promote
 *    products derived from this software without prior written permission
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * <end of "sniffer.c" terms>
 *
 * This software, "sniffex.c", is a derivative work of "sniffer.c" and is
 * covered by the following terms:
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Because this is a derivative work, you must comply with the "sniffer.c"
 *    terms reproduced above.
 * 2. Redistributions of source code must retain the Tcpdump Group copyright
 *    notice at the top of this source file, this list of conditions and the
 *    following disclaimer.
 * 3. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. The names "tcpdump" or "libpcap" may not be used to endorse or promote
 *    products derived from this software without prior written permission.
 *
 * THERE IS ABSOLUTELY NO WARRANTY FOR THIS PROGRAM.
 * BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
 * FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
 * OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
 * PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
 * OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
 * TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
 * PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
 * REPAIR OR CORRECTION.
 *
 * IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
 * WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
 * REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
 * INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
 * OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
 * TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
 * YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
 * PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGES.
 * <end of "sniffex.c" terms>
 *
 ****************************************************************************
 *
 * Below is an excerpt from an email from Guy Harris on the tcpdump-workers
 * mail list when someone asked, "How do I get the length of the TCP
 * payload?" Guy Harris' slightly snipped response (edited by him to
 * speak of the IPv4 header length and TCP data offset without referring
 * to bitfield structure members) is reproduced below:
 *
 * The Ethernet size is always 14 bytes.
 *
 * <snip>...</snip>
 *
 * In fact, you *MUST* assume the Ethernet header is 14 bytes, *and*, if
 * you're using structures, you must use structures where the members
 * always have the same size on all platforms, because the sizes of the
 * fields in Ethernet - and IP, and TCP, and... - headers are defined by
 * the protocol specification, not by the way a particular platform's C
 * compiler works.)
 *
 * The IP header size, in bytes, is the value of the IP header length,
 * as extracted from the "ip_vhl" field of "struct sniff_ip" with
 * the "IP_HL()" macro, times 4 ("times 4" because it's in units of
 * 4-byte words).  If that value is less than 20 - i.e., if the value
 * extracted with "IP_HL()" is less than 5 - you have a malformed
 * IP datagram.
 *
 * The TCP header size, in bytes, is the value of the TCP data offset,
 * as extracted from the "th_offx2" field of "struct sniff_tcp" with
 * the "TH_OFF()" macro, times 4 (for the same reason - 4-byte words).
 * If that value is less than 20 - i.e., if the value extracted with
 * "TH_OFF()" is less than 5 - you have a malformed TCP segment.
 *
 * So, to find the IP header in an Ethernet packet, look 14 bytes after
 * the beginning of the packet data.  To find the TCP header, look
 * "IP_HL(ip)*4" bytes after the beginning of the IP header.  To find the
 * TCP payload, look "TH_OFF(tcp)*4" bytes after the beginning of the TCP
 * header.
 *
 * To find out how much payload there is:
 *
 * Take the IP *total* length field - "ip_len" in "struct sniff_ip"
 * - and, first, check whether it's less than "IP_HL(ip)*4" (after
 * you've checked whether "IP_HL(ip)" is >= 5).  If it is, you have
 * a malformed IP datagram.
 *
 * Otherwise, subtract "IP_HL(ip)*4" from it; that gives you the length
 * of the TCP segment, including the TCP header.  If that's less than
 * "TH_OFF(tcp)*4" (after you've checked whether "TH_OFF(tcp)" is >= 5),
 * you have a malformed TCP segment.
 *
 * Otherwise, subtract "TH_OFF(tcp)*4" from it; that gives you the
 * length of the TCP payload.
 *
 * Note that you also need to make sure that you don't go past the end
 * of the captured data in the packet - you might, for example, have a
 * 15-byte Ethernet packet that claims to contain an IP datagram, but if
 * it's 15 bytes, it has only one byte of Ethernet payload, which is too
 * small for an IP header.  The length of the captured data is given in
 * the "caplen" field in the "struct pcap_pkthdr"; it might be less than
 * the length of the packet, if you're capturing with a snapshot length
 * other than a value >= the maximum packet size.
 * <end of response>
 *
 ****************************************************************************
 *
 * Example compiler command-line for GCC:
 *   gcc -Wall -o sniffex sniffex.c -lpcap
 *
 ****************************************************************************
 *
 * Code Comments
 *
 * This section contains additional information and explanations regarding
 * comments in the source code. It serves as documentaion and rationale
 * for why the code is written as it is without hindering readability, as it
 * might if it were placed along with the actual code inline. References in
 * the code appear as footnote notation (e.g. [1]).
 *
 * 1. Ethernet headers are always exactly 14 bytes, so we define this
 * explicitly with "#define". Since some compilers might pad structures to a
 * multiple of 4 bytes - some versions of GCC for ARM may do this -
 * "sizeof (struct sniff_ethernet)" isn't used.
 *
 * 2. Check the link-layer type of the device that's being opened to make
 * sure it's Ethernet, since that's all we handle in this example. Other
 * link-layer types may have different length headers (see [1]).
 *
 * 3. This is the filter expression that tells libpcap which packets we're
 * interested in (i.e. which packets to capture). Since this source example
 * focuses on IP and TCP, we use the expression "ip", so we know we'll only
 * encounter IP packets. The capture filter syntax, along with some
 * examples, is documented in the tcpdump man page under "expression."
 * Below are a few simple examples:
 *
 * Expression   Description
 * ----------   -----------
 * ip     Capture all IP packets.
 * tcp     Capture only TCP packets.
 * tcp port 80   Capture only TCP packets with a port equal to 80.
 * ip host 10.1.2.3  Capture all IP packets to or from host 10.1.2.3.
 *
 ****************************************************************************
 *
 */

#define APP_NAME  "sniffex"
#define APP_DESC  "Sniffer example using libpcap"
#define APP_COPYRIGHT "Copyright (c) 2005 The Tcpdump Group"
#define APP_DISCLAIMER "THERE IS ABSOLUTELY NO WARRANTY FOR THIS PROGRAM."

#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>

/* 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 */
};

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_banner(void);

void
print_app_usage(void);

/*
 * app name/banner
 */
void
print_app_banner(void)
{

 printf("%s - %s\n", APP_NAME, APP_DESC);
 printf("%s\n", APP_COPYRIGHT);
 printf("%s\n", APP_DISCLAIMER);
 printf("\n");

return;
}

/*
 * print help text
 */
void
print_app_usage(void)
{

 printf("Usage: %s [interface]\n", APP_NAME);
 printf("\n");
 printf("Options:\n");
 printf("    interface    Listen on <interface> for packets.\n");
 printf("\n");

return;
}

/*
 * print data in rows of 16 bytes: offset   hex   ascii
 *
 * 00000   47 45 54 20 2f 20 48 54  54 50 2f 31 2e 31 0d 0a   GET / HTTP/1.1..
 */
void
print_hex_ascii_line(const u_char *payload, int len, int offset)
{

 int i;
 int gap;
 const u_char *ch;

 /* offset */
 printf("%05d   ", offset);
 
 /* hex */
 ch = payload;
 for(i = 0; i < len; i++) {
  printf("%02x ", *ch);
  ch++;
  /* print extra space after 8th byte for visual aid */
  if (i == 7)
   printf(" ");
 }
 /* print space to handle line less than 8 bytes */
 if (len < 8)
  printf(" ");
 
 /* fill hex gap with spaces if not full line */
 if (len < 16) {
  gap = 16 - len;
  for (i = 0; i < gap; i++) {
   printf("   ");
  }
 }
 printf("   ");
 
 /* ascii (if printable) */
 ch = payload;
 for(i = 0; i < len; i++) {
  if (isprint(*ch))
   printf("%c", *ch);
  else
   printf(".");
  ch++;
 }

 printf("\n");

return;
}

/*
 * print packet payload data (avoid printing binary data)
 */
void
print_payload(const u_char *payload, int len)
{

 int len_rem = len;
 int line_width = 16;   /* number of bytes per line */
 int line_len;
 int offset = 0;     /* zero-based offset counter */
 const u_char *ch = payload;

 if (len <= 0)
  return;

 /* data fits on one line */
 if (len <= line_width) {
  print_hex_ascii_line(ch, len, offset);
  return;
 }

 /* data spans multiple lines */
 for ( ;; ) {
  /* compute current line length */
  line_len = line_width % len_rem;
  /* print line */
  print_hex_ascii_line(ch, line_len, offset);
  /* compute total remaining */
  len_rem = len_rem - line_len;
  /* shift pointer to remaining bytes to print */
  ch = ch + line_len;
  /* add offset */
  offset = offset + line_width;
  /* check if we have line width chars or less */
  if (len_rem <= line_width) {
   /* print last line and get out */
   print_hex_ascii_line(ch, len_rem, offset);
   break;
  }
 }

return;
}

/*
 * dissect/print packet
 */
void
got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet)
{

 static int count = 1;                   /* packet counter */
 
 /* 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;
 }

 /* print source and destination IP addresses */
 printf("       From: %s\n", inet_ntoa(ip->ip_src));
 printf("         To: %s\n", inet_ntoa(ip->ip_dst));
 
 /* determine protocol */ 
 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;
 }
 
 /*
  *  OK, this packet is TCP.
  */
 
 /* 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;
 }
 
 printf("   Src port: %d\n", ntohs(tcp->th_sport));
 printf("   Dst port: %d\n", ntohs(tcp->th_dport));
 
 /* define/compute tcp payload (segment) offset */
 payload = (u_char *)(packet + SIZE_ETHERNET + size_ip + size_tcp);
 
 /* compute tcp payload (segment) size */
 size_payload = ntohs(ip->ip_len) - (size_ip + size_tcp);
 
 /*
  * Print payload data; it might be binary, so don't just
  * treat it as a string.
  */
 if (size_payload > 0) {
  printf("   Payload (%d bytes):\n", size_payload);
  print_payload(payload, 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[] = "ip";  /* filter expression [3] */
 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 */

 print_app_banner();

 /* 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("Number of packets: %d\n", num_packets);
 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);
 }

 /* now we can set our callback function */
 pcap_loop(handle, num_packets, got_packet, NULL);

 /* cleanup */
 pcap_freecode(&fp);
 pcap_close(handle);

 printf("\nCapture complete.\n");

return 0;
}

 

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