/*

 *

 *  libnet 1.1

 *  Build a GRE packet

 *  To view: tcpdump -s 0 -n -X -vvv proto gre

 *

 *  Copyright (c) 2003 Frédéric Raynal <pappy@security-labs.org>

 *  All rights reserved.

 *

 *

 *  KNOWN BUG

 *    the encapsulated headers have wrong checksums. I guess this is due to

 *    the one pass libnet_pblock_coalesce() which is really to complicated :(

 *

 *

 *  Default packet:

 *   # ./gre -d 1.2.3.4                

 *   libnet 1.1 packet shaping: GRE 1701 [link]

 *   Wrote 78 byte GRE packet; check the wire.

 *

 *   18:58:12.112157 192.168.1.2 > 1.2.3.4: gre 198.35.123.50.1234 > 103.69.139.107.53: S [bad tcp cksum 698a!] 16843009:16843009(0) win 32767 (ttl 64, id 242, len 40, bad cksum 0!) (ttl 255, id 255, len 64)

 *   0x0000   4500 0040 00ff 0000 ff2f f4df c0a8 0102        E..@...../......

 *   0x0010   0102 0304 0000 0800 4500 0028 00f2 0000        ........E..(....

 *   0x0020   4006 0000 c623 7b32 6745 8b6b 04d2 0035        @....#{2gE.k...5

 *   0x0030   0101 0101 0202 0202 5002 7fff 6666 0000        ........P...ff..

 *

 *  Packet with a computed checksum 

 *   # ./gre -d 1.2.3.4 -c 0

 *   libnet 1.1 packet shaping: GRE 1701 [link]

 *   Wrote 82 byte GRE packet; check the wire.

 *   

 *   18:58:22.587513 192.168.1.2 > 1.2.3.4: gre [Cv0] C:7c62 198.35.123.50.1234 > 103.69.139.107.53: S [bad tcp cksum 698a!] 16843009:16843009(0) win 32767 (ttl 64, id 242, len 40, bad cksum 0!) (ttl 255, id 255, len 68)

 *   0x0000   4500 0044 00ff 0000 ff2f f4db c0a8 0102        E..D...../......

 *   0x0010   0102 0304 8000 0800 7c62 0000 4500 0028        ........|b..E..(

 *   0x0020   00f2 0000 4006 0000 c623 7b32 6745 8b6b        ....@....#{2gE.k

 *   0x0030   04d2 0035 0101 0101 0202 0202 5002 7fff        ...5........P...

 *   0x0040   6666 0000                                      ff..

 *

 *

 *  Packet with a forced checksum 

 *   # ./gre -d 1.2.3.4 -c 6666

 *   libnet 1.1 packet shaping: GRE 1701 [link]

 *   Wrote 68 byte GRE packet; check the wire.

 *   

 *   19:04:12.108080 192.168.1.2 > 1.2.3.4: gre [Cv0] C:1a0a 198.35.123.50.1234 > 103.69.139.107.53: S [bad tcp cksum 698a!] 16843009:16843009(0) win 32767 (ttl 64, id 242, len 40, bad cksum 0!) (ttl 255, id 255, len 68)

 *   0x0000   4500 0044 00ff 0000 ff2f f4db c0a8 0102        E..D...../......

 *   0x0010   0102 0304 8000 0800 1a0a 0000 4500 0028        ............E..(

 *   0x0020   00f2 0000 4006 0000 c623 7b32 6745 8b6b        ....@....#{2gE.k

 *   0x0030   04d2 0035 0101 0101 0202 0202 5002 7fff        ...5........P...

 *   0x0040   6666 0000                                      ff..

 *

 *

 * 

 *

 * 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.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.

 *

 */

#if (HAVE_CONFIG_H)

#include "../include/config.h"

#endif

#include "./libnet_test.h"

void

usage(char *prog)

{

    fprintf(stderr, "Usage: %s\n", prog);

    fprintf(stderr, "\t IP options:  -d <dst ip> [-s src ip]\n");

    fprintf(stderr, "\t GRE options: [-v] set RFC 2637 mode (PPP in GRE) (default is RFC 1701 for IP in GRE)\n");

    fprintf(stderr, "\t\t RFC 1701 options (IP in GRE):\n");

    fprintf(stderr, "\t\t   [-c sum]  [-r routing] [-k key] [-n seqnum]\n");

    fprintf(stderr, "\t\t   IP in GRE options: [-S src ip]  [-D dst ip]\n");

    fprintf(stderr, "\t\t RFC 2637 options (PPP in GRE):\n");

    fprintf(stderr, "\t\t   [-a ack]\n");

    exit(1);

}

/*

 *                ---------------------------------

 *                |       Delivery Header         |

 *                ---------------------------------

 *                |       GRE Header              |

 *               ---------------------------------

 *                |       Payload packet          |

 *                ---------------------------------

 */

int

main(int argc, char *argv[])

{

    char c;

    libnet_t *l;

    char errbuf[LIBNET_ERRBUF_SIZE];

    u_long src_ip = 0, dst_ip = 0, gre_src_ip = 0, gre_dst_ip = 0;

    u_short checksum = 0, offset = 0;

    u_char *routing = NULL;

    u_long key = 0, seq = 0;

    u_short gre_flags = 0;

    u_long len;

    u_long size = 0;

    libnet_ptag_t t;

    printf("libnet 1.1 packet shaping: GRE [link]\n");

    /*

     *  Initialize the library.  Root priviledges are required.

     */

    l = libnet_init(

            LIBNET_LINK,                            /* injection type */

            NULL,                                   /* network interface */

            errbuf);                                /* error buffer */

    if (!l)

    {

        fprintf(stderr, "libnet_init: %s", errbuf);

        exit(EXIT_FAILURE);

    }

    /*

     * parse options

     */

    while ((c = getopt(argc, argv, "d:s:D:S:c:r:k:n:va:")) != EOF)

    {

        switch (c)

        {

            case 'd':

                if ((dst_ip = libnet_name2addr4(l, optarg, LIBNET_RESOLVE)) == -1)

                {

                    fprintf(stderr, "Bad destination IP address: %s\n", optarg);

                    exit(EXIT_FAILURE);

                }

                break;

            case 's':

                if ((src_ip = libnet_name2addr4(l, optarg, LIBNET_RESOLVE)) == -1)

                {

                    fprintf(stderr, "Bad source IP address: %s\n", optarg);

                    exit(EXIT_FAILURE);

                }

                break;

            case 'D':

                if ((gre_dst_ip = libnet_name2addr4(l, optarg, LIBNET_RESOLVE)) == -1)

                {

                    fprintf(stderr, "Bad destination IP address (GRE): %s\n", optarg);

                    exit(EXIT_FAILURE);

                }

                break;

            case 'S':

                if ((gre_src_ip = libnet_name2addr4(l, optarg, LIBNET_RESOLVE)) == -1)

                {

                    fprintf(stderr, "Bad source IP address (GRE): %s\n", optarg);

                    exit(EXIT_FAILURE);

                }

                break;

	    case 'c':

		checksum = atoi(optarg);

		gre_flags|=GRE_CSUM;

                break;

	    case 'r':

		routing = optarg;

		gre_flags|=GRE_ROUTING;

                break;

	    case 'k':

		key = atoi(optarg);

		gre_flags|=GRE_KEY;

                break;

	    case 'n':

		seq = atoi(optarg);

		gre_flags|=GRE_SEQ;

                break;

	    case 'v':

		gre_flags|=(GRE_VERSION_1|GRE_KEY);

		break;

	    case 'a':

		if (! (gre_flags & GRE_VERSION_1))

		    usage(argv[0]);

		seq = atoi(optarg);    /* seq in v0 is ack in v1 */

		gre_flags|=GRE_ACK;

		break;

            default:

                exit(EXIT_FAILURE);

        }

    }

    /*

     * check options 

     */

    if (!dst_ip)

    {

	usage(argv[0]);

    }

    if (!src_ip)

    {

	src_ip = libnet_get_ipaddr4(l);

    }

    if (!gre_dst_ip)

    {

	gre_dst_ip = libnet_get_prand(LIBNET_PRu32);

    }

    if (!gre_src_ip)

    {

	gre_src_ip = libnet_get_prand(LIBNET_PRu32);

    }

    if ( (gre_flags & GRE_VERSION_MASK) == 0)

    {

	/*

	 * Build a TCP/IP packet embedded in GRE message

	 */

	size = LIBNET_TCP_H;

	t = libnet_build_tcp(

	    1234,                                       /* source port */

	    53,                                         /* destination port */

	    0x01010101,                                 /* sequence number */

	    0x02020202,                                 /* acknowledgement num */

	    TH_SYN,                                     /* control flags */

	    32767,                                      /* window size */

	    0,                                          /* checksum */

	    0,                                          /* urgent pointer */

	    size,                                       /* TCP packet size */

	    NULL,                                       /* payload */

	    0,                                          /* payload size */

	    l,                                          /* libnet handle */

	    0);                                         /* libnet id */

	if (t == -1)

	{

	    fprintf(stderr, "Can't build TCP header (GRE): %s\n", libnet_geterror(l));

	    goto bad;

	}

	size += LIBNET_IPV4_H;

	t = libnet_build_ipv4(

	    size,                                       /* length */

	    0,                                          /* TOS */

	    242,                                        /* IP ID */

	    0,                                          /* IP Frag */

	    64,                                         /* TTL */

	    IPPROTO_TCP,                                /* protocol */

	    0,                                          /* checksum */

	    gre_src_ip,                                 /* source IP */

	    gre_dst_ip,                                 /* destination IP */

	    NULL,                                       /* payload */

	    0,                                          /* payload size */

	    l,                                          /* libnet handle */

	    0);                                         /* libnet id */

	if (t == -1)

	{

	    fprintf(stderr, "Can't build IP header (GRE): %s\n", libnet_geterror(l));

	    goto bad;

	} 

    }

    if ( (gre_flags & GRE_VERSION_MASK) == 1)

    {

	offset = libnet_get_prand(LIBNET_PRu16);

	if (~gre_flags & GRE_ACK)

	{

	    u_char ppp[4] = "\x00\x01"; /* PPP padding */

	    checksum = 2; /* checksum is in fact payload_s in PPP/GRE (v1) */

	    size = 2;

	    gre_flags|=GRE_SEQ;

	    key = libnet_get_prand(LIBNET_PRu32);

	    /*

	     * Build a PPP packet embedded in GRE message

	     */

	    t = libnet_build_data(

		ppp,

		checksum,

		l, 

		0

	    );

	    if (t == -1)

	    {

		fprintf(stderr, "Can't build PPP header (GRE): %s\n", libnet_geterror(l));

		goto bad;

	    }

	}

	gre_flags&=~(GRE_CSUM|GRE_ROUTING);

    }

    /*

     * Build the GRE message

     */

    if (gre_flags & GRE_ROUTING)

    {

	/* as packet are stacked, start by the last one, ie null sre */

	size += LIBNET_GRE_SRE_H;

	t = libnet_build_gre_last_sre(l, 0);

	if (t == -1)

	{

	    fprintf(stderr, "Can't build GRE last SRE header: %s\n", libnet_geterror(l));

	    goto bad;

	}

	size += LIBNET_GRE_SRE_H + strlen(routing);

	t = libnet_build_gre_sre(

	    GRE_IP,                                 /* address family */

	    0,                                      /* offset */

	    strlen(routing),                        /* routing length */

	    routing,                                /* routing info */

	    NULL,                                   /* payload */

	    0,                                      /* payload size */

	    l,                                      /* libnet handle */

	    0);                                     /* libnet id */

	if (t == -1)

	{

	    fprintf(stderr, "Can't build GRE last SRE header: %s\n", libnet_geterror(l));

	    goto bad;

	}

    }

    len = libnet_getgre_length(gre_flags);

    size += len;

    t = libnet_build_gre(

        gre_flags,                                  /* flags & version */

        (gre_flags & GRE_VERSION_1 ? GRE_PPP : GRE_IP), /* type */

        checksum,                                   /* v0: checksum / v1: payload_s */

        offset,                                     /* v0: offset   / v1: callID    */

        key,                                        /* v0: key      / v1: seq bum   */

        seq,                                        /* v0: seq num  / v1: ack       */

	size,                                       /* length */

        NULL,                                       /* payload */

        0,                                          /* payload size */

        l,                                          /* libnet handle */

        0);                                         /* libnet id */

    if (t == -1)

    {

        fprintf(stderr, "Can't build GRE header: %s\n", libnet_geterror(l));

        goto bad;

    }

    /*

     * Build the "real" IP header

     */

    size+=LIBNET_IPV4_H;

    t = libnet_build_ipv4(

        size,                                       /* length */

        0,                                          /* TOS */

        255,                                        /* IP ID */

        0,                                          /* IP Frag */

        255,                                        /* TTL */

        IPPROTO_GRE,                                /* protocol */

        0,                                          /* checksum */

        src_ip,                                     /* source IP */

        dst_ip,                                     /* destination IP */

        NULL,                                       /* payload */

        0,                                          /* payload size */

        l,                                          /* libnet handle */

        0);                                         /* libnet id */

    if (t == -1)

    {

        fprintf(stderr, "Can't build IP header (GRE): %s\n", libnet_geterror(l));

        goto bad;

    } 

    t = libnet_autobuild_ethernet(

            "11:11:11:11:11:11",                                    /* ethernet destination */

            ETHERTYPE_IP,                          /* protocol type */

            l);                                     /* libnet handle */

    if (t == -1)

    {

        fprintf(stderr, "Can't build ethernet header: %s\n",

                libnet_geterror(l));

        goto bad;

    }

    /*

     *  Write it to the wire.

     */

    c = libnet_write(l);

    if (c == -1)

    {

        fprintf(stderr, "Write error: %s\n", libnet_geterror(l));

        goto bad;

    }

    else

    {

        fprintf(stderr, "Wrote %d byte GRE packet; check the wire.\n", c);

    }

    libnet_destroy(l);

    return (EXIT_SUCCESS);

bad:

    libnet_destroy(l);

    return (EXIT_FAILURE); 

}