ipxe/src/net/udp/dhcp.c

/*
 * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <string.h>
#include <assert.h>
#include <byteswap.h>
#include <gpxe/netdevice.h>
#include <gpxe/dhcp.h>

/** @file
 *
 * Dynamic Host Configuration Protocol
 *
 */

/**
 * Calculate used length of a field containing DHCP options
 *
 * @v data		Field containing DHCP options
 * @v max_len		Field length
 * @ret len		Used length (excluding the @c DHCP_END tag)
 */
static size_t dhcp_field_len ( const void *data, size_t max_len ) {
	struct dhcp_option_block options;
	struct dhcp_option *end;

	options.data = ( ( void * ) data );
	options.len = max_len;
	end = find_dhcp_option ( &options, DHCP_END );
	return ( end ? ( ( ( void * ) end ) - data ) : 0 );
}

/**
 * Merge field containing DHCP options or string into DHCP options block
 *
 * @v options		DHCP option block
 * @v data		Field containing DHCP options
 * @v max_len		Field length
 * @v tag		DHCP option tag, or 0
 *
 * If @c tag is non-zero, the field will be treated as a
 * NUL-terminated string representing the value of the specified DHCP
 * option.  If @c tag is zero, the field will be treated as a block of
 * DHCP options, and simply appended to the existing options in the
 * option block.
 *
 * The caller must ensure that there is enough space in the options
 * block to perform the merge.
 */
static void merge_dhcp_field ( struct dhcp_option_block *options,
			       const void *data, size_t max_len,
			       unsigned int tag ) {
	size_t len;
	void *dest;
	struct dhcp_option *end;

	if ( tag ) {
		set_dhcp_option ( options, tag, data, strlen ( data ) );
	} else {
		len = dhcp_field_len ( data, max_len );
		dest = ( options->data + options->len - 1 );
		memcpy ( dest, data, len );
		options->len += len;
		end = ( dest + len );
		end->tag = DHCP_END;
	}
}

/**
 * Parse DHCP packet and construct DHCP options block
 *
 * @v data		DHCP packet
 * @v len		Length of DHCP packet
 * @ret options		DHCP options block, or NULL
 *
 * Parses a received DHCP packet and canonicalises its contents into a
 * single DHCP options block.  The "file" and "sname" fields are
 * converted into the corresponding DHCP options (@c
 * DHCP_BOOTFILE_NAME and @c DHCP_TFTP_SERVER_NAME respectively).  If
 * these fields are used for option overloading, their options are
 * merged in to the options block.  The values of the "yiaddr" and
 * "siaddr" fields will be stored within the options block as the
 * options @c DHCP_EB_YIADDR and @c DHCP_EB_SIADDR.
 * 
 * Note that this call allocates new memory for the constructed DHCP
 * options block; it is the responsibility of the caller to eventually
 * free this memory.
 */
struct dhcp_option_block * dhcp_parse ( const void *data, size_t len ) {
	const struct dhcp_packet *dhcppkt = data;
	struct dhcp_option_block *options;
	size_t options_len;
	unsigned int overloading;

	/* Calculate size of resulting concatenated option block:
	 *
	 *   The "options" field : length of the field minus the DHCP_END tag.
	 *
	 *   The "file" field : maximum length of the field minus the
	 *   NUL terminator, plus a 2-byte DHCP header or, if used for
	 *   option overloading, the length of the field minus the
	 *   DHCP_END tag.
	 *
	 *   The "sname" field : as for the "file" field.
	 *
	 *   15 bytes for an encapsulated options field to contain the
	 *   value of the "yiaddr" and "siaddr" fields
	 *
	 *   1 byte for a final terminating DHCP_END tag.
	 */
	options_len = ( ( len - offsetof ( typeof ( *dhcppkt ), options ) ) - 1
			+ ( sizeof ( dhcppkt->file ) + 1 )
			+ ( sizeof ( dhcppkt->sname ) + 1 )
			+ 15 /* yiaddr and siaddr */
			+ 1 /* DHCP_END tag */ );
	
	/* Allocate empty options block of required size */
	options = alloc_dhcp_options ( options_len );
	if ( ! options ) {
		DBG ( "DHCP could not allocate %d-byte option block\n",
		      options_len );
		return NULL;
	}
	
	/* Merge in "options" field, if this is a DHCP packet */
	if ( dhcppkt->magic == htonl ( DHCP_MAGIC_COOKIE ) ) {
		merge_dhcp_field ( options, dhcppkt->options,
				   ( len -
				     offsetof ( typeof (*dhcppkt), options ) ),
				   0 /* Always contains options */ );
	}

	/* Identify overloaded fields */
	overloading = find_dhcp_num_option ( options, DHCP_OPTION_OVERLOAD );
	
	/* Merge in "file" and "sname" fields */
	merge_dhcp_field ( options, dhcppkt->file, sizeof ( dhcppkt->file ),
			   ( ( overloading & DHCP_OPTION_OVERLOAD_FILE ) ?
			     DHCP_BOOTFILE_NAME : 0 ) );
	merge_dhcp_field ( options, dhcppkt->sname, sizeof ( dhcppkt->sname ),
			   ( ( overloading & DHCP_OPTION_OVERLOAD_SNAME ) ?
			     DHCP_TFTP_SERVER_NAME : 0 ) );

	/* Set options for "yiaddr" and "siaddr", if present */
	if ( dhcppkt->yiaddr.s_addr ) {
		set_dhcp_option ( options, DHCP_EB_YIADDR,
				  &dhcppkt->yiaddr, sizeof (dhcppkt->yiaddr) );
	}
	if ( dhcppkt->siaddr.s_addr ) {
		set_dhcp_option ( options, DHCP_EB_SIADDR,
				  &dhcppkt->siaddr, sizeof (dhcppkt->siaddr) );
	}
	
	assert ( options->len <= options->max_len );

	return options;
}