Annotation of embedaddon/libnet/doc/PACKET_BUILDING, revision 1.1
1.1 ! misho 1: ===============================================================================
! 2: $Id: PACKET_BUILDING,v 1.2 2004/01/03 20:31:00 mike Exp $
! 3: LIBNET 1.1 (c) 1998 - 2004 Mike D. Schiffman <mike@infonexus.com>
! 4: http://www.packetfactory.net/libnet
! 5: ===============================================================================
! 6:
! 7:
! 8: ADDING A NEW PACKET BUILDER
! 9:
! 10: Adding a new packet building module is usually pretty simple. It depends
! 11: completely on the complexity of the protocol. The following document
! 12: shows you how to add a packet builder for a simple protocol with a
! 13: static header size, but these concepts can be extended to a complex
! 14: protocol also.
! 15:
! 16: 1) Start by defining your protocol header format in libnet-headers.h:
! 17:
! 18: #define LIBNET_XXX_H 0xSIZE
! 19:
! 20: struct XXX_hdr
! 21: {
! 22: u_char field1;
! 23: u_short field2;
! 24: u_long field3;
! 25: };
! 26:
! 27: 2) Add a pblock definition to libnet-structures.h (appened to the list):
! 28:
! 29: #define LIBNET_PBLOCK_XXX_H 0xNUMBER
! 30:
! 31: 3) Then work from the following template for libnet_build_XXX.c:
! 32:
! 33: #if (HAVE_CONFIG_H)
! 34: #include "../include/config.h"
! 35: #endif
! 36: #include "../include/libnet.h"
! 37:
! 38:
! 39: libnet_ptag_t
! 40: libnet_build_XXX(u_char arg1, u_short arg2, u_long arg3, u_char *payload,
! 41: u_long payload_s, libnet_t *l, libnet_ptag_t ptag)
! 42: {
! 43: /*
! 44: * n is the size of the protocol unit. This is usually the header size
! 45: * plus the payload size. This is also how many bytes are allocated on
! 46: * the heap to hold this protocol unit.
! 47: */
! 48: u_long n;
! 49:
! 50: /*
! 51: * h is used inside the pblock structure to let libnet know how big
! 52: * much data to checksum. This is different for different protocols.
! 53: * The IPv4 checksum covers the IP header only, while TCP and UDP
! 54: * checksums cover header and data.
! 55: */
! 56: u_short h;
! 57:
! 58: /*
! 59: * p will be used to refer to the protocol block that will either be
! 60: * allocated if the function's pt argument is 0, or located if ptag refers
! 61: * to a previously created protocol unit.
! 62: */
! 63: libnet_pblock_t *p;
! 64:
! 65: /*
! 66: * XXX_hdr is the header structure that will be overlaid onto the
! 67: * allocated memory by way of a memcpy.
! 68: */
! 69: struct libnet_XXX_hdr XXX_hdr;
! 70:
! 71: /*
! 72: * Here we sanity check to make sure we have a live l.
! 73: */
! 74: if (l == NULL)
! 75: {
! 76: return (-1);
! 77: }
! 78:
! 79: n = LIBNET_XXX_H + payload_s;
! 80: h = 0; /* no checksum by default */
! 81:
! 82: /*
! 83: * Find the existing protocol block if a ptag is specified, or create
! 84: * a new one.
! 85: */
! 86: p = libnet_pblock_probe(l, pt, n, LIBNET_PBLOCK_XXX_H);
! 87: if (p == NULL)
! 88: {
! 89: return (-1);
! 90: }
! 91:
! 92: /*
! 93: * Build your packet here. Be sure to call appropriate endian conversion
! 94: * routines.
! 95: */
! 96: XXX_hdr.field1 = arg1;
! 97: XXX_hdr.field2 = htons(arg2);
! 98: XXX_hdr.field3 = htonl(arg3);
! 99:
! 100: /*
! 101: * Appened the protocol unit to the list.
! 102: */
! 103: n = libnet_pblock_append(l, p, (u_char *)&XXX_hdr, LIBNET_XXX_H);
! 104: if (n == -1)
! 105: {
! 106: goto bad;
! 107: }
! 108:
! 109: /*
! 110: * Sanity check the payload arguments.
! 111: */
! 112: if ((payload && !payload_s) || (!payload && payload_s))
! 113: {
! 114: sprintf(l->err_buf, "%s(): payload inconsistency\n", __FUNCTION__);
! 115: goto bad;
! 116: }
! 117:
! 118: /*
! 119: * Append the payload to the list if it exists.
! 120: */
! 121: if (payload && payload_s)
! 122: {
! 123: n = libnet_pblock_append(l, p, payload, payload_s);
! 124: if (n == -1)
! 125: {
! 126: goto bad;
! 127: }
! 128: }
! 129:
! 130: /*
! 131: * If this packet header has a checksum field, you'll add this
! 132: * and you'll have to edit libnet_checksum.c to add it to the switch
! 133: * table. You might have to define the protocol number too.
! 134: */
! 135: if (sum == 0 && l->injection_type != LIBNET_RAW4)
! 136: {
! 137: /*
! 138: * If checksum is zero, by default libnet will compute a checksum
! 139: * for the user. The programmer can override this by calling
! 140: * libnet_toggle_checksum(l, ptag, 1);
! 141: */
! 142: libnet_pblock_setflags(p, LIBNET_PBLOCK_DO_CHECKSUM);
! 143: }
! 144:
! 145: /*
! 146: * Update the protocol block's meta information and return the protocol
! 147: * tag id of this pblock. This tag will be used to locate the pblock
! 148: * in order to modify the protocol header in subsequent calls.
! 149: */
! 150: return (pt ? pt : libnet_pblock_update(l, p, h, LIBNET_PBLOCK_XXX_H));
! 151: bad:
! 152: libnet_pblock_delete(l, p);
! 153: return (-1);
! 154:
! 155: }
! 156: 4) Add it to src/Makefile.am and then automake from the TLD.
! 157: 5) Test the shit out of it.
! 158: 6) Send it over to mike@infonexus.com.
! 159:
! 160:
! 161: EOF
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