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Diffstat (limited to 'libnet/doc/PACKET_BUILDING')
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diff --git a/libnet/doc/PACKET_BUILDING b/libnet/doc/PACKET_BUILDING new file mode 100644 index 0000000..2470f74 --- /dev/null +++ b/libnet/doc/PACKET_BUILDING @@ -0,0 +1,161 @@ +=============================================================================== + $Id: PACKET_BUILDING,v 1.2 2004/01/03 20:31:00 mike Exp $ + LIBNET 1.1 (c) 1998 - 2004 Mike D. Schiffman <mike@infonexus.com> + http://www.packetfactory.net/libnet +=============================================================================== + + + ADDING A NEW PACKET BUILDER + + Adding a new packet building module is usually pretty simple. It depends + completely on the complexity of the protocol. The following document + shows you how to add a packet builder for a simple protocol with a + static header size, but these concepts can be extended to a complex + protocol also. + + 1) Start by defining your protocol header format in libnet-headers.h: + + #define LIBNET_XXX_H 0xSIZE + + struct XXX_hdr + { + u_char field1; + u_short field2; + u_long field3; + }; + + 2) Add a pblock definition to libnet-structures.h (appened to the list): + + #define LIBNET_PBLOCK_XXX_H 0xNUMBER + + 3) Then work from the following template for libnet_build_XXX.c: + +#if (HAVE_CONFIG_H) +#include "../include/config.h" +#endif +#include "../include/libnet.h" + + +libnet_ptag_t +libnet_build_XXX(u_char arg1, u_short arg2, u_long arg3, u_char *payload, + u_long payload_s, libnet_t *l, libnet_ptag_t ptag) +{ + /* + * n is the size of the protocol unit. This is usually the header size + * plus the payload size. This is also how many bytes are allocated on + * the heap to hold this protocol unit. + */ + u_long n; + + /* + * h is used inside the pblock structure to let libnet know how big + * much data to checksum. This is different for different protocols. + * The IPv4 checksum covers the IP header only, while TCP and UDP + * checksums cover header and data. + */ + u_short h; + + /* + * p will be used to refer to the protocol block that will either be + * allocated if the function's pt argument is 0, or located if ptag refers + * to a previously created protocol unit. + */ + libnet_pblock_t *p; + + /* + * XXX_hdr is the header structure that will be overlaid onto the + * allocated memory by way of a memcpy. + */ + struct libnet_XXX_hdr XXX_hdr; + + /* + * Here we sanity check to make sure we have a live l. + */ + if (l == NULL) + { + return (-1); + } + + n = LIBNET_XXX_H + payload_s; + h = 0; /* no checksum by default */ + + /* + * Find the existing protocol block if a ptag is specified, or create + * a new one. + */ + p = libnet_pblock_probe(l, pt, n, LIBNET_PBLOCK_XXX_H); + if (p == NULL) + { + return (-1); + } + + /* + * Build your packet here. Be sure to call appropriate endian conversion + * routines. + */ + XXX_hdr.field1 = arg1; + XXX_hdr.field2 = htons(arg2); + XXX_hdr.field3 = htonl(arg3); + + /* + * Appened the protocol unit to the list. + */ + n = libnet_pblock_append(l, p, (u_char *)&XXX_hdr, LIBNET_XXX_H); + if (n == -1) + { + goto bad; + } + + /* + * Sanity check the payload arguments. + */ + if ((payload && !payload_s) || (!payload && payload_s)) + { + sprintf(l->err_buf, "%s(): payload inconsistency\n", __FUNCTION__); + goto bad; + } + + /* + * Append the payload to the list if it exists. + */ + if (payload && payload_s) + { + n = libnet_pblock_append(l, p, payload, payload_s); + if (n == -1) + { + goto bad; + } + } + + /* + * If this packet header has a checksum field, you'll add this + * and you'll have to edit libnet_checksum.c to add it to the switch + * table. You might have to define the protocol number too. + */ + if (sum == 0 && l->injection_type != LIBNET_RAW4) + { + /* + * If checksum is zero, by default libnet will compute a checksum + * for the user. The programmer can override this by calling + * libnet_toggle_checksum(l, ptag, 1); + */ + libnet_pblock_setflags(p, LIBNET_PBLOCK_DO_CHECKSUM); + } + + /* + * Update the protocol block's meta information and return the protocol + * tag id of this pblock. This tag will be used to locate the pblock + * in order to modify the protocol header in subsequent calls. + */ + return (pt ? pt : libnet_pblock_update(l, p, h, LIBNET_PBLOCK_XXX_H)); +bad: + libnet_pblock_delete(l, p); + return (-1); + +} + 4) Add it to src/Makefile.am and then automake from the TLD. + 5) Test the shit out of it. + 6) Send it over to mike@infonexus.com. + + +EOF |