/* * Copyright (C) 2006 Michael Brown . * * 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 #include #include #include #include #include /** @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, }; /** * Set option within DHCP packet * * @v dhcppkt DHCP packet * @v tag DHCP option tag * @v data New value for DHCP option * @v len Length of value, in bytes * @ret rc Return status code * * 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. * * The magic options @c DHCP_EB_YIADDR and @c DHCP_EB_SIADDR are * intercepted and inserted into the appropriate fixed fields within * the DHCP packet. The option @c DHCP_OPTION_OVERLOAD is silently * ignored, since our DHCP packet assembly method relies on always * having option overloading in use. */ static int set_dhcp_packet_option ( struct dhcp_packet *dhcppkt, unsigned int tag, const void *data, size_t len ) { struct dhcphdr *dhcphdr = dhcppkt->dhcphdr; struct dhcp_option_block *options; struct dhcp_option *option = NULL; /* Special-case the magic options */ switch ( tag ) { case DHCP_OPTION_OVERLOAD: /* Hard-coded in packets we create; always ignore */ return 0; case DHCP_EB_YIADDR: memcpy ( &dhcphdr->yiaddr, data, sizeof ( dhcphdr->yiaddr ) ); return 0; case DHCP_EB_SIADDR: memcpy ( &dhcphdr->siaddr, data, sizeof ( dhcphdr->siaddr ) ); return 0; default: /* Continue processing as normal */ break; } /* Set option in first available options block */ for ( options = dhcppkt->options ; options < &dhcppkt->options[NUM_OPT_BLOCKS] ; options++ ) { option = set_dhcp_option ( options, tag, data, len ); if ( option ) break; } /* Update DHCP packet length */ dhcppkt->len = ( offsetof ( typeof ( *dhcppkt->dhcphdr ), options ) + dhcppkt->options[OPTS_MAIN].len ); return ( option ? 0 : -ENOSPC ); } /** * Set options within DHCP packet * * @v dhcppkt DHCP packet * @v options DHCP option block, or NULL * @v encapsulator Encapsulating option, or zero * @ret rc Return status code * * Copies options with the specified encapsulator from DHCP options * blocks into a DHCP packet. Most options are copied verbatim. * Recognised encapsulated options fields are handled as such. * * @c options may specify a single options block, or be left as NULL * in order to copy options from all registered options blocks. */ static int set_dhcp_packet_encap_options ( struct dhcp_packet *dhcppkt, struct dhcp_option_block *options, unsigned int encapsulator ) { unsigned int subtag; unsigned int tag; struct dhcp_option *option; int rc; for ( subtag = DHCP_MIN_OPTION; subtag <= DHCP_MAX_OPTION; subtag++ ) { tag = DHCP_ENCAP_OPT ( encapsulator, subtag ); switch ( tag ) { case DHCP_EB_ENCAP: case DHCP_VENDOR_ENCAP: /* Process encapsulated options field */ if ( ( rc = set_dhcp_packet_encap_options ( dhcppkt, options, tag )) !=0) return rc; break; default: /* Copy option to reassembled packet */ option = find_dhcp_option ( options, tag ); if ( ! option ) break; if ( ( rc = set_dhcp_packet_option ( dhcppkt, tag, &option->data, option->len)) !=0) return rc; break; }; } return 0; } /** * Set options within DHCP packet * * @v dhcppkt DHCP packet * @v options DHCP option block, or NULL * @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. * * @c options may specify a single options block, or be left as NULL * in order to copy options from all registered options blocks. */ static int set_dhcp_packet_options ( struct dhcp_packet *dhcppkt, struct dhcp_option_block *options ) { return set_dhcp_packet_encap_options ( dhcppkt, options, 0 ); } /** * Create a DHCP packet * * @v dhcp DHCP session * @v msgtype DHCP message type * @v data Buffer for DHCP packet * @v max_len Size of DHCP packet buffer * @v dhcppkt DHCP packet structure to fill in * @ret rc Return status code * * Creates a DHCP packet in the specified buffer, and fills out a @c * dhcp_packet structure that can be passed to * set_dhcp_packet_option() or set_dhcp_packet_options(). */ int create_dhcp_packet ( struct dhcp_session *dhcp, uint8_t msgtype, void *data, size_t max_len, struct dhcp_packet *dhcppkt ) { struct dhcphdr *dhcphdr = data; static const uint8_t overloading = ( DHCP_OPTION_OVERLOAD_FILE | DHCP_OPTION_OVERLOAD_SNAME ); /* Initialise DHCP packet structure */ dhcppkt->dhcphdr = dhcphdr; dhcppkt->max_len = max_len; init_dhcp_options ( &dhcppkt->options[OPTS_MAIN], dhcphdr->options, ( max_len - offsetof ( typeof ( *dhcphdr ), options ) ) ); init_dhcp_options ( &dhcppkt->options[OPTS_FILE], dhcphdr->file, sizeof ( dhcphdr->file ) ); init_dhcp_options ( &dhcppkt->options[OPTS_SNAME], dhcphdr->sname, sizeof ( dhcphdr->sname ) ); /* Initialise DHCP packet content */ memset ( dhcphdr, 0, max_len ); dhcphdr->xid = dhcp->xid; dhcphdr->magic = htonl ( DHCP_MAGIC_COOKIE ); dhcphdr->htype = ntohs ( dhcp->netdev->ll_protocol->ll_proto ); dhcphdr->hlen = dhcp->netdev->ll_protocol->ll_addr_len; memcpy ( dhcphdr->chaddr, dhcp->netdev->ll_addr, dhcphdr->hlen ); dhcphdr->op = dhcp_op[msgtype]; /* Set DHCP_OPTION_OVERLOAD option within the main options block */ if ( ! set_dhcp_option ( &dhcppkt->options[OPTS_MAIN], DHCP_OPTION_OVERLOAD, &overloading, sizeof ( overloading ) ) ) return -ENOSPC; /* Set DHCP_MESSAGE_TYPE option */ if ( ! set_dhcp_packet_option ( dhcppkt, DHCP_MESSAGE_TYPE, &msgtype, sizeof ( msgtype ) ) ) return -ENOSPC; return 0; } /** * 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 magic 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 dhcphdr *dhcphdr = data; struct dhcp_option_block *options; size_t options_len; unsigned int overloading; /* Sanity check */ if ( len < sizeof ( *dhcphdr ) ) 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 ( *dhcphdr ), options ) ) - 1 + ( sizeof ( dhcphdr->file ) + 1 ) + ( sizeof ( dhcphdr->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 ( dhcphdr->magic == htonl ( DHCP_MAGIC_COOKIE ) ) { merge_dhcp_field ( options, dhcphdr->options, ( len - offsetof ( typeof (*dhcphdr), 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, dhcphdr->file, sizeof ( dhcphdr->file ), ( ( overloading & DHCP_OPTION_OVERLOAD_FILE ) ? DHCP_BOOTFILE_NAME : 0 ) ); merge_dhcp_field ( options, dhcphdr->sname, sizeof ( dhcphdr->sname ), ( ( overloading & DHCP_OPTION_OVERLOAD_SNAME ) ? DHCP_TFTP_SERVER_NAME : 0 ) ); /* Set magic options for "yiaddr" and "siaddr", if present */ if ( dhcphdr->yiaddr.s_addr ) { set_dhcp_option ( options, DHCP_EB_YIADDR, &dhcphdr->yiaddr, sizeof (dhcphdr->yiaddr) ); } if ( dhcphdr->siaddr.s_addr ) { set_dhcp_option ( options, DHCP_EB_SIADDR, &dhcphdr->siaddr, sizeof (dhcphdr->siaddr) ); } assert ( options->len <= options->max_len ); return options; }