/*
* 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 <errno.h>
#include <assert.h>
#include <byteswap.h>
#include <gpxe/netdevice.h>
#include <gpxe/dhcp.h>
/** @file
*
* Dynamic Host Configuration Protocol
*
*/
/** DHCP operation types
*
* This table maps from DHCP message types (i.e. values of the @c
* DHCP_MESSAGE_TYPE option) to values of the "op" field within a DHCP
* packet.
*/
static const uint8_t dhcp_op[] = {
[DHCPDISCOVER] = BOOTP_REQUEST,
[DHCPOFFER] = BOOTP_REPLY,
[DHCPREQUEST] = BOOTP_REQUEST,
[DHCPDECLINE] = BOOTP_REQUEST,
[DHCPACK] = BOOTP_REPLY,
[DHCPNAK] = BOOTP_REPLY,
[DHCPRELEASE] = BOOTP_REQUEST,
[DHCPINFORM] = BOOTP_REQUEST,
};
/** DHCP packet option block fill order
*
* This is the order in which option blocks are filled when
* reassembling a DHCP packet. We fill the smallest field ("sname")
* first, to maximise the chances of being able to fit large options
* within fields which are large enough to contain them.
*/
enum dhcp_packet_option_block_fill_order {
OPTS_SNAME = 0,
OPTS_FILE,
OPTS_MAIN,
NUM_OPT_BLOCKS
};
/** DHCP option blocks within a DHCP packet
*
* A DHCP packet contains three fields which can be used to contain
* options: the actual "options" field plus the "file" and "sname"
* fields (which can be overloaded to contain options).
*/
struct dhcp_packet_option_blocks {
struct dhcp_option_block options[NUM_OPT_BLOCKS];
};
/**
* Set option within DHCP packet
*
* @v optblocks DHCP packet option blocks
* @v tag DHCP option tag
* @v data New value for DHCP option
* @v len Length of value, in bytes
* @ret option DHCP option, or NULL
*
* Sets the option within the first available options block within the
* DHCP packet. Option blocks are tried in the order specified by @c
* dhcp_option_block_fill_order.
*/
static struct dhcp_option *
set_dhcp_packet_option ( struct dhcp_packet_option_blocks *optblocks,
unsigned int tag, const void *data, size_t len ) {
struct dhcp_option_block *options;
struct dhcp_option *option;
for ( options = optblocks->options ;
options < &optblocks->options[NUM_OPT_BLOCKS] ; options++ ) {
option = set_dhcp_option ( options, tag, data, len );
if ( option )
return option;
}
return NULL;
}
/**
* Copy options to DHCP packet
*
* @v optblocks DHCP packet option blocks
* @v encapsulator Encapsulating option, or zero
* @ret rc Return status code
*
* Copies options from DHCP options blocks into a DHCP packet. Most
* options are copied verbatim. Recognised encapsulated options
* fields are handled as such. Selected options (e.g. @c
* DHCP_OPTION_OVERLOAD) are always ignored, since these special cases
* are handled by other code.
*/
static int
copy_dhcp_options_to_packet ( struct dhcp_packet_option_blocks *optblocks,
unsigned int encapsulator ) {
unsigned int subtag;
unsigned int tag;
struct dhcp_option *option;
struct dhcp_option *copied;
int rc;
for ( subtag = DHCP_MIN_OPTION; subtag <= DHCP_MAX_OPTION; subtag++ ) {
tag = DHCP_ENCAP_OPT ( encapsulator, subtag );
switch ( tag ) {
case DHCP_OPTION_OVERLOAD:
/* Hard-coded in packets we reassemble; skip
* this option
*/
break;
case DHCP_EB_ENCAP:
case DHCP_VENDOR_ENCAP:
/* Process encapsulated options field */
if ( ( rc = copy_dhcp_options_to_packet ( optblocks,
tag ) ) != 0)
return rc;
break;
default:
/* Copy option to reassembled packet */
option = find_global_dhcp_option ( tag );
if ( ! option )
break;
copied = set_dhcp_packet_option ( optblocks, tag,
&option->data,
option->len );
if ( ! copied )
return -ENOSPC;
break;
};
}
return 0;
}
/**
* Assemble a DHCP packet
*
* @v dhcp DHCP session
* @v data Packet to be filled in
* @v max_len Length of packet buffer
* @ret len Length of assembled packet
*
* Reconstruct a DHCP packet from a DHCP options list.
*/
size_t dhcp_assemble ( struct dhcp_session *dhcp, void *data,
size_t max_len ) {
struct dhcp_packet *dhcppkt = data;
struct dhcp_option *option;
struct dhcp_packet_option_blocks optblocks;
unsigned int dhcp_message_type;
static const uint8_t overloading = ( DHCP_OPTION_OVERLOAD_FILE |
DHCP_OPTION_OVERLOAD_SNAME );
/* Fill in constant fields */
memset ( dhcppkt, 0, max_len );
dhcppkt->xid = dhcp->xid;
dhcppkt->magic = htonl ( DHCP_MAGIC_COOKIE );
/* Derive "op" field from DHCP_MESSAGE_TYPE option value */
dhcp_message_type = find_global_dhcp_num_option ( DHCP_MESSAGE_TYPE );
dhcppkt->op = dhcp_op[dhcp_message_type];
/* Fill in NIC details */
dhcppkt->htype = ntohs ( dhcp->netdev->ll_protocol->ll_proto );
dhcppkt->hlen = dhcp->netdev->ll_protocol->ll_addr_len;
memcpy ( dhcppkt->chaddr, dhcp->netdev->ll_addr, dhcppkt->hlen );
/* Fill in IP addresses if present */
option = find_global_dhcp_option ( DHCP_EB_YIADDR );
if ( option ) {
memcpy ( &dhcppkt->yiaddr, &option->data,
sizeof ( dhcppkt->yiaddr ) );
}
option = find_global_dhcp_option ( DHCP_EB_SIADDR );
if ( option ) {
memcpy ( &dhcppkt->siaddr, &option->data,
sizeof ( dhcppkt->siaddr ) );
}
/* Initialise option blocks */
init_dhcp_options ( &optblocks.options[OPTS_MAIN], dhcppkt->options,
( max_len -
offsetof ( typeof ( *dhcppkt ), options ) ) );
init_dhcp_options ( &optblocks.options[OPTS_FILE], dhcppkt->file,
sizeof ( dhcppkt->file ) );
init_dhcp_options ( &optblocks.options[OPTS_SNAME], dhcppkt->sname,
sizeof ( dhcppkt->sname ) );
set_dhcp_option ( &optblocks.options[OPTS_MAIN], DHCP_OPTION_OVERLOAD,
&overloading, sizeof ( overloading ) );
/* Populate option blocks */
copy_dhcp_options_to_packet ( &optblocks, 0 );
return ( offsetof ( typeof ( *dhcppkt ), options )
+ optblocks.options[OPTS_MAIN].len );
}
/**
* 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;
/* Sanity check */
if ( len < sizeof ( *dhcppkt ) )
return NULL;
/* 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;
}
