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[gpxe.git] / 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 <errno.h>
#include <assert.h>
#include <byteswap.h>
#include <gpxe/if_ether.h>
#include <gpxe/netdevice.h>
#include <gpxe/udp.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,
};

/** Raw option data for options common to all DHCP requests */
static uint8_t dhcp_request_options_data[] = {
        DHCP_MAX_MESSAGE_SIZE, DHCP_WORD ( ETH_MAX_MTU ),
        DHCP_VENDOR_CLASS_ID,
        DHCP_STRING (  'E', 't', 'h', 'e', 'r', 'b', 'o', 'o', 't' ),
        DHCP_PARAMETER_REQUEST_LIST,
        DHCP_OPTION ( DHCP_SUBNET_MASK, DHCP_ROUTERS, DHCP_HOST_NAME ),
        DHCP_END
};

/**
 * Name a DHCP packet type
 *
 * @v msgtype           DHCP message type
 * @ret string          DHCP mesasge type name
 */
static inline const char * dhcp_msgtype_name ( unsigned int msgtype ) {
        switch ( msgtype ) {
        case 0:                 return "BOOTP"; /* Non-DHCP packet */
        case DHCPDISCOVER:      return "DHCPDISCOVER";
        case DHCPOFFER:         return "DHCPOFFER";
        case DHCPREQUEST:       return "DHCPREQUEST";
        case DHCPDECLINE:       return "DHCPDECLINE";
        case DHCPACK:           return "DHCPACK";
        case DHCPNAK:           return "DHCPNAK";
        case DHCPRELEASE:       return "DHCPRELEASE";
        case DHCPINFORM:        return "DHCPINFORM";
        default:                return "DHCP<invalid>";
        }
}

/** Options common to all DHCP requests */
static struct dhcp_option_block dhcp_request_options = {
        .data = dhcp_request_options_data,
        .max_len = sizeof ( dhcp_request_options_data ),
        .len = sizeof ( dhcp_request_options_data ),
};

/**
 * 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 = dhcppkt->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;
        case DHCP_MESSAGE_TYPE:
        case DHCP_REQUESTED_ADDRESS:
                /* These options have to be within the main options
                 * block.  This doesn't seem to be required by the
                 * RFCs, but at least ISC dhcpd refuses to recognise
                 * them otherwise.
                 */
                options = &dhcppkt->options[OPTS_MAIN];
                break;
        default:
                /* Continue processing as normal */
                break;
        }
                
        /* Set option in first available options block */
        for ( ; 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 );
}

/**
 * Copy option into DHCP packet
 *
 * @v dhcppkt           DHCP packet
 * @v options           DHCP option block, or NULL
 * @v tag               DHCP option tag to search for
 * @v new_tag           DHCP option tag to use for copied option
 * @ret rc              Return status code
 *
 * Copies a single option, if present, from the DHCP options block
 * into a DHCP packet.  The tag for the option may be changed if
 * desired; this is required by other parts of the DHCP code.
 *
 * @c options may specify a single options block, or be left as NULL
 * in order to search for the option within all registered options
 * blocks.
 */
static int copy_dhcp_packet_option ( struct dhcp_packet *dhcppkt,
                                     struct dhcp_option_block *options,
                                     unsigned int tag, unsigned int new_tag ) {
        struct dhcp_option *option;
        int rc;

        option = find_dhcp_option ( options, tag );
        if ( option ) {
                if ( ( rc = set_dhcp_packet_option ( dhcppkt, new_tag,
                                                     &option->data,
                                                     option->len ) ) != 0 )
                        return rc;
        }
        return 0;
}

/**
 * Copy options into 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 copy_dhcp_packet_encap_options ( struct dhcp_packet *dhcppkt,
                                            struct dhcp_option_block *options,
                                            unsigned int encapsulator ) {
        unsigned int subtag;
        unsigned int tag;
        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 = copy_dhcp_packet_encap_options ( dhcppkt,
                                                                     options,
                                                                     tag)) !=0)
                                return rc;
                        break;
                default:
                        /* Copy option to reassembled packet */
                        if ( ( rc = copy_dhcp_packet_option ( dhcppkt, options,
                                                              tag, tag ) ) !=0)
                                return rc;
                        break;
                };
        }

        return 0;
}

/**
 * Copy options into 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 copy_dhcp_packet_options ( struct dhcp_packet *dhcppkt,
                                      struct dhcp_option_block *options ) {
        return copy_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 copy_dhcp_packet_options().
 */
static 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 );
        int rc;

        /* Sanity check */
        if ( max_len < sizeof ( *dhcphdr ) )
                return -ENOSPC;

        /* 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];

        /* 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 ) );
        
        /* Set DHCP_OPTION_OVERLOAD option within the main options block */
        if ( set_dhcp_option ( &dhcppkt->options[OPTS_MAIN],
                               DHCP_OPTION_OVERLOAD, &overloading,
                               sizeof ( overloading ) ) == NULL )
                return -ENOSPC;

        /* Set DHCP_MESSAGE_TYPE option */
        if ( ( rc = set_dhcp_packet_option ( dhcppkt, DHCP_MESSAGE_TYPE,
                                             &msgtype,
                                             sizeof ( msgtype ) ) ) != 0 )
                return rc;

        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 dhcphdr           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.
 */
static struct dhcp_option_block * dhcp_parse ( struct dhcphdr *dhcphdr,
                                               size_t len ) {
        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;
}

/****************************************************************************
 *
 * DHCP to UDP interface
 *
 */

static inline struct dhcp_session *
udp_to_dhcp ( struct udp_connection *conn ) {
        return container_of ( conn, struct dhcp_session, udp );
}

/**
 * Mark DHCP session as complete
 *
 * @v dhcp              DHCP session
 * @v rc                Return status code
 */
static void dhcp_done ( struct dhcp_session *dhcp, int rc ) {
        /* Mark async operation as complete */
        async_done ( &dhcp->aop, rc );
}

/** Address for transmitting DHCP requests */
static struct sockaddr sa_dhcp_server = {
        .sa_family = AF_INET,
        .sin = {
                .sin_addr.s_addr = INADDR_BROADCAST,
                .sin_port = htons ( BOOTPS_PORT ),
        },
};

/**
 * Transmit DHCP request
 *
 * @v conn              UDP connection
 * @v buf               Temporary data buffer
 * @v len               Length of temporary data buffer
 */
static void dhcp_senddata ( struct udp_connection *conn,
                            void *buf, size_t len ) {
        struct dhcp_session *dhcp = udp_to_dhcp ( conn );
        struct dhcp_packet dhcppkt;
        int rc;
        
        DBG ( "Transmitting %s\n", dhcp_msgtype_name ( dhcp->state ) );

        assert ( ( dhcp->state == DHCPDISCOVER ) ||
                 ( dhcp->state == DHCPREQUEST ) );

        /* Create DHCP packet in temporary buffer */
        if ( ( rc = create_dhcp_packet ( dhcp, dhcp->state, buf, len,
                                         &dhcppkt ) ) != 0 ) {
                DBG ( "Could not create DHCP packet\n" );
                return;
        }

        /* Copy in options common to all requests */
        if ( ( rc = copy_dhcp_packet_options ( &dhcppkt,
                                               &dhcp_request_options ) ) != 0){
                DBG ( "Could not set common DHCP options\n" );
                return;
        }

        /* Copy any required options from previous server repsonse */
        if ( dhcp->options ) {
                if ( ( rc = copy_dhcp_packet_option ( &dhcppkt, dhcp->options,
                                            DHCP_SERVER_IDENTIFIER,
                                            DHCP_SERVER_IDENTIFIER ) ) != 0 ) {
                        DBG ( "Could not set server identifier option\n" );
                        return;
                }
                if ( ( rc = copy_dhcp_packet_option ( &dhcppkt, dhcp->options,
                                            DHCP_EB_YIADDR,
                                            DHCP_REQUESTED_ADDRESS ) ) != 0 ) {
                        DBG ( "Could not set requested address option\n" );
                        return;
                }
        }

        /* Transmit the packet */
        if ( ( rc = udp_sendto ( conn, &sa_dhcp_server,
                                 dhcppkt.dhcphdr, dhcppkt.len ) ) != 0 ) {
                DBG ( "Could not transmit UDP packet\n" );
                return;
        }
}

/**
 * Transmit DHCP request
 *
 * @v dhcp              DHCP session
 */
static void dhcp_send_request ( struct dhcp_session *dhcp ) {
        start_timer ( &dhcp->timer );
        udp_senddata ( &dhcp->udp );
}

/**
 * Handle DHCP retry timer expiry
 *
 * @v timer             DHCP retry timer
 * @v fail              Failure indicator
 */
static void dhcp_timer_expired ( struct retry_timer *timer, int fail ) {
        struct dhcp_session *dhcp =
                container_of ( timer, struct dhcp_session, timer );

        if ( fail ) {
                dhcp_done ( dhcp, -ETIMEDOUT );
        } else {
                dhcp_send_request ( dhcp );
        }
}

/**
 * Receive new data
 *
 * @v udp               UDP connection
 * @v data              Received data
 * @v len               Length of received data
 */
static void dhcp_newdata ( struct udp_connection *conn,
                           void *data, size_t len ) {
        struct dhcp_session *dhcp = udp_to_dhcp ( conn );
        struct dhcphdr *dhcphdr = data;
        struct dhcp_option_block *options;
        unsigned int msgtype;

        /* Check for matching transaction ID */
        if ( dhcphdr->xid != dhcp->xid ) {
                DBG ( "DHCP wrong transaction ID (wanted %08lx, got %08lx)\n",
                      ntohl ( dhcphdr->xid ), ntohl ( dhcp->xid ) );
                return;
        };

        /* Parse packet and create options structure */
        options = dhcp_parse ( dhcphdr, len );
        if ( ! options ) {
                DBG ( "Could not parse DHCP packet\n" );
                return;
        }

        /* Determine message type */
        msgtype = find_dhcp_num_option ( options, DHCP_MESSAGE_TYPE );
        DBG ( "Received %s\n", dhcp_msgtype_name ( msgtype ) );

        /* Handle DHCP reply */
        switch ( dhcp->state ) {
        case DHCPDISCOVER:
                if ( msgtype != DHCPOFFER )
                        goto out_discard;
                dhcp->state = DHCPREQUEST;
                break;
        case DHCPREQUEST:
                if ( msgtype != DHCPACK )
                        goto out_discard;
                dhcp->state = DHCPACK;
                break;
        default:
                assert ( 0 );
                goto out_discard;
        }

        /* Stop timer and update stored options */
        stop_timer ( &dhcp->timer );
        if ( dhcp->options )
                free_dhcp_options ( dhcp->options );
        dhcp->options = options;

        /* Transmit next packet, or terminate session */
        if ( dhcp->state < DHCPACK ) {
                dhcp_send_request ( dhcp );
        } else {
                dhcp_done ( dhcp, 0 );
        }
        return;

 out_discard:
        free_dhcp_options ( options );
}

/** DHCP UDP operations */
static struct udp_operations dhcp_udp_operations = {
        .senddata       = dhcp_senddata,
        .newdata        = dhcp_newdata,
};

/**
 * Initiate DHCP on a network interface
 *
 * @v dhcp              DHCP session
 * @ret aop             Asynchronous operation
 *
 * If the DHCP operation completes successfully, the
 * dhcp_session::options field will be filled in with the resulting
 * options block.  The caller takes responsibility for eventually
 * calling free_dhcp_options().
 */
struct async_operation * start_dhcp ( struct dhcp_session *dhcp ) {
        int rc;

        /* Initialise DHCP session */
        dhcp->udp.udp_op = &dhcp_udp_operations;
        dhcp->timer.expired = dhcp_timer_expired;
        dhcp->state = DHCPDISCOVER;
        /* Use least significant 32 bits of link-layer address as XID */
        memcpy ( &dhcp->xid, ( dhcp->netdev->ll_addr
                               + dhcp->netdev->ll_protocol->ll_addr_len
                               - sizeof ( dhcp->xid ) ), sizeof ( dhcp->xid ));

        /* Bind to local port */
        if ( ( rc = udp_open ( &dhcp->udp, htons ( BOOTPC_PORT ) ) ) != 0 ) {
                async_done ( &dhcp->aop, rc );
                goto out;
        }

        /* Proof of concept: just send a single DHCPDISCOVER */
        dhcp_send_request ( dhcp );

 out:
        return &dhcp->aop;
}