Add (untested) code for parsing a received DHCP packet and constructing a
DHCP options block from the contents.
This commit is contained in:
Michael Brown
parent
19e8b41562
commit
12da7ea475
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@ -9,6 +9,87 @@
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#include <stdint.h>
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#include <gpxe/list.h>
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#include <gpxe/in.h>
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/**
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* A DHCP packet
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*
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*/
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struct dhcp_packet {
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/** Operation
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*
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* This must be either @c BOOTP_REQUEST or @c BOOTP_REPLY.
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*/
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uint8_t op;
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/** Hardware address type
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*
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* This is an ARPHRD_XXX constant.
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*/
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uint8_t htype;
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/** Hardware address length */
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uint8_t hlen;
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/** Number of hops from server */
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uint8_t hops;
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/** Transaction ID */
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uint32_t xid;
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/** Seconds since start of acquisition */
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uint16_t secs;
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/** Flags */
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uint16_t flags;
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/** "Client" IP address
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*
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* This is filled in if the client already has an IP address
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* assigned and can respond to ARP requests.
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*/
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struct in_addr ciaddr;
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/** "Your" IP address
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*
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* This is the IP address assigned by the server to the client.
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*/
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struct in_addr yiaddr;
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/** "Server" IP address
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*
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* This is the IP address of the next server to be used in the
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* boot process.
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*/
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struct in_addr siaddr;
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/** "Gateway" IP address
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*
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* This is the IP address of the DHCP relay agent, if any.
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*/
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struct in_addr giaddr;
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/** Client hardware address */
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uint8_t chaddr[16];
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/** Server host name (null terminated)
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*
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* This field may be overridden and contain DHCP options
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*/
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uint8_t sname[64];
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/** Boot file name (null terminated)
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*
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* This field may be overridden and contain DHCP options
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*/
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uint8_t file[128];
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/** DHCP magic cookie
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*
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* Must have the value @c DHCP_MAGIC_COOKIE.
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*/
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uint32_t magic;
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/** DHCP options
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*
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* Variable length; extends to the end of the packet.
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*/
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uint8_t options[0];
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};
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/** Opcode for a request from client to server */
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#define BOOTP_REQUEST 1
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/** Opcode for a reply from server to client */
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#define BOOTP_REPLY 2
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/** DHCP magic cookie */
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#define DHCP_MAGIC_COOKIE 0x63825363UL
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/** Construct a tag value for an encapsulated option
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*
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@ -22,7 +103,7 @@
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#define DHCP_ENCAPSULATOR( encap_opt ) ( (encap_opt) >> 8 )
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/** Extract encapsulated option tag from encapsulated tag value */
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#define DHCP_ENCAPSULATED( encap_opt ) ( (encap_opt) & 0xff )
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/** Option is encapsulated */
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#define DHCP_IS_ENCAP_OPT( opt ) DHCP_ENCAPSULATOR( opt )
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/**
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@ -30,13 +111,80 @@
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* @{
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*/
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/** Padding
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*
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* This tag does not have a length field; it is always only a single
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* byte in length.
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*/
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#define DHCP_PAD 0
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#define DHCP_END 255
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/** Option overloading
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*
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* The value of this option is the bitwise-OR of zero or more
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* DHCP_OPTION_OVERLOAD_XXX constants.
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*/
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#define DHCP_OPTION_OVERLOAD 52
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/** The "file" field is overloaded to contain extra DHCP options */
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#define DHCP_OPTION_OVERLOAD_FILE 1
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/** The "sname" field is overloaded to contain extra DHCP options */
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#define DHCP_OPTION_OVERLOAD_SNAME 2
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/** TFTP server name
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*
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* This option replaces the fixed "sname" field, when that field is
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* used to contain overloaded options.
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*/
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#define DHCP_TFTP_SERVER_NAME 66
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/** Bootfile name
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*
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* This option replaces the fixed "file" field, when that field is
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* used to contain overloaded options.
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*/
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#define DHCP_BOOTFILE_NAME 67
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/** Etherboot-specific encapsulated options
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*
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* This encapsulated options field is used to contain all options
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* specific to Etherboot (i.e. not assigned by IANA or other standards
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* bodies).
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*/
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#define DHCP_EB_ENCAP 175
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/** Priority of this options block
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*
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* This is a signed 8-bit integer field indicating the priority of
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* this block of options. It can be used to specify the relative
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* priority of multiple option blocks (e.g. options from non-volatile
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* storage versus options from a DHCP server).
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*/
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#define DHCP_EB_PRIORITY DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 1 )
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/** "Your" IP address
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*
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* This option is used internally to contain the value of the "yiaddr"
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* field, in order to provide a consistent approach to storing and
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* processing options. It should never be present in a DHCP packet.
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*/
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#define DHCP_EB_YIADDR DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 2 )
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/** "Server" IP address
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*
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* This option is used internally to contain the value of the "siaddr"
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* field, in order to provide a consistent approach to storing and
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* processing options. It should never be present in a DHCP packet.
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*/
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#define DHCP_EB_SIADDR DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 3 )
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/** End of options
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*
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* This tag does not have a length field; it is always only a single
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* byte in length.
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*/
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#define DHCP_END 255
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/** @} */
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/**
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@ -118,7 +266,6 @@ extern struct dhcp_option *
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set_dhcp_option ( struct dhcp_option_block *options, unsigned int tag,
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const void *data, size_t len );
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/**
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* Find DHCP numerical option, and return its value
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*
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@ -0,0 +1,172 @@
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/*
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* Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <string.h>
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#include <assert.h>
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#include <byteswap.h>
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#include <gpxe/netdevice.h>
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#include <gpxe/dhcp.h>
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/** @file
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*
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* Dynamic Host Configuration Protocol
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*
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*/
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/**
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* Calculate used length of a field containing DHCP options
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*
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* @v data Field containing DHCP options
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* @v max_len Field length
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* @ret len Used length (excluding the @c DHCP_END tag)
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*/
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static size_t dhcp_field_len ( const void *data, size_t max_len ) {
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struct dhcp_option_block options;
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struct dhcp_option *end;
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options.data = ( ( void * ) data );
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options.len = max_len;
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end = find_dhcp_option ( &options, DHCP_END );
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return ( end ? ( ( ( void * ) end ) - data ) : 0 );
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}
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/**
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* Merge field containing DHCP options or string into DHCP options block
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*
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* @v options DHCP option block
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* @v data Field containing DHCP options
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* @v max_len Field length
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* @v tag DHCP option tag, or 0
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*
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* If @c tag is non-zero, the field will be treated as a
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* NUL-terminated string representing the value of the specified DHCP
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* option. If @c tag is zero, the field will be treated as a block of
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* DHCP options, and simply appended to the existing options in the
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* option block.
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*
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* The caller must ensure that there is enough space in the options
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* block to perform the merge.
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*/
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static void merge_dhcp_field ( struct dhcp_option_block *options,
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const void *data, size_t max_len,
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unsigned int tag ) {
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size_t len;
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void *dest;
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struct dhcp_option *end;
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if ( tag ) {
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set_dhcp_option ( options, tag, data, strlen ( data ) );
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} else {
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len = dhcp_field_len ( data, max_len );
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dest = ( options->data + options->len - 1 );
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memcpy ( dest, data, len );
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options->len += len;
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end = ( dest + len );
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end->tag = DHCP_END;
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}
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}
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/**
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* Parse DHCP packet and construct DHCP options block
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*
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* @v data DHCP packet
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* @v len Length of DHCP packet
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* @ret options DHCP options block, or NULL
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*
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* Parses a received DHCP packet and canonicalises its contents into a
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* single DHCP options block. The "file" and "sname" fields are
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* converted into the corresponding DHCP options (@c
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* DHCP_BOOTFILE_NAME and @c DHCP_TFTP_SERVER_NAME respectively). If
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* these fields are used for option overloading, their options are
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* merged in to the options block. The values of the "yiaddr" and
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* "siaddr" fields will be stored within the options block as the
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* options @c DHCP_EB_YIADDR and @c DHCP_EB_SIADDR.
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*
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* Note that this call allocates new memory for the constructed DHCP
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* options block; it is the responsibility of the caller to eventually
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* free this memory.
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*/
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struct dhcp_option_block * dhcp_parse ( const void *data, size_t len ) {
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const struct dhcp_packet *dhcppkt = data;
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struct dhcp_option_block *options;
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size_t options_len;
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unsigned int overloading;
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/* Calculate size of resulting concatenated option block:
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*
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* The "options" field : length of the field minus the DHCP_END tag.
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*
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* The "file" field : maximum length of the field minus the
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* NUL terminator, plus a 2-byte DHCP header or, if used for
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* option overloading, the length of the field minus the
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* DHCP_END tag.
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*
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* The "sname" field : as for the "file" field.
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*
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* 15 bytes for an encapsulated options field to contain the
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* value of the "yiaddr" and "siaddr" fields
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*
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* 1 byte for a final terminating DHCP_END tag.
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*/
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options_len = ( ( len - offsetof ( typeof ( *dhcppkt ), options ) ) - 1
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+ ( sizeof ( dhcppkt->file ) + 1 )
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+ ( sizeof ( dhcppkt->sname ) + 1 )
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+ 15 /* yiaddr and siaddr */
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+ 1 /* DHCP_END tag */ );
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/* Allocate empty options block of required size */
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options = alloc_dhcp_options ( options_len );
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if ( ! options ) {
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DBG ( "DHCP could not allocate %d-byte option block\n",
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options_len );
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return NULL;
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}
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/* Merge in "options" field, if this is a DHCP packet */
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if ( dhcppkt->magic == htonl ( DHCP_MAGIC_COOKIE ) ) {
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merge_dhcp_field ( options, dhcppkt->options,
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( len -
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offsetof ( typeof (*dhcppkt), options ) ),
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0 /* Always contains options */ );
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}
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/* Identify overloaded fields */
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overloading = find_dhcp_num_option ( options, DHCP_OPTION_OVERLOAD );
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/* Merge in "file" and "sname" fields */
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merge_dhcp_field ( options, dhcppkt->file, sizeof ( dhcppkt->file ),
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( ( overloading & DHCP_OPTION_OVERLOAD_FILE ) ?
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DHCP_BOOTFILE_NAME : 0 ) );
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merge_dhcp_field ( options, dhcppkt->sname, sizeof ( dhcppkt->sname ),
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( ( overloading & DHCP_OPTION_OVERLOAD_SNAME ) ?
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DHCP_TFTP_SERVER_NAME : 0 ) );
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/* Set options for "yiaddr" and "siaddr", if present */
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if ( dhcppkt->yiaddr.s_addr ) {
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set_dhcp_option ( options, DHCP_EB_YIADDR,
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&dhcppkt->yiaddr, sizeof (dhcppkt->yiaddr) );
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}
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if ( dhcppkt->siaddr.s_addr ) {
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set_dhcp_option ( options, DHCP_EB_SIADDR,
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&dhcppkt->siaddr, sizeof (dhcppkt->siaddr) );
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}
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assert ( options->len <= options->max_len );
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return options;
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}
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