/* * 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 #include #include #include #include /** @file * * DHCP options * */ /** List of registered DHCP option blocks */ static LIST_HEAD ( option_blocks ); /** * Obtain printable version of a DHCP option tag * * @v tag DHCP option tag * @ret name String representation of the tag * */ static inline char * dhcp_tag_name ( unsigned int tag ) { static char name[8]; if ( DHCP_IS_ENCAP_OPT ( tag ) ) { snprintf ( name, sizeof ( name ), "%d.%d", DHCP_ENCAPSULATOR ( tag ), DHCP_ENCAPSULATED ( tag ) ); } else { snprintf ( name, sizeof ( name ), "%d", tag ); } return name; } /** * Obtain value of a numerical DHCP option * * @v option DHCP option, or NULL * @ret value Numerical value of the option, or 0 * * Parses the numerical value from a DHCP option, if present. It is * permitted to call dhcp_num_option() with @c option set to NULL; in * this case 0 will be returned. * * The caller does not specify the size of the DHCP option data; this * is implied by the length field stored within the DHCP option * itself. */ unsigned long dhcp_num_option ( struct dhcp_option *option ) { unsigned long value = 0; uint8_t *data; if ( option ) { /* This is actually smaller code than using htons() * etc., and will also cope well with malformed * options (such as zero-length options). */ for ( data = option->data.bytes ; data < ( option->data.bytes + option->len ) ; data++ ) value = ( ( value << 8 ) | *data ); } return value; } /** * Obtain value of an IPv4-address DHCP option * * @v option DHCP option, or NULL * @v inp IPv4 address to fill in * * Parses the IPv4 address value from a DHCP option, if present. It * is permitted to call dhcp_ipv4_option() with @c option set to NULL; * in this case the address will be set to 0.0.0.0. */ void dhcp_ipv4_option ( struct dhcp_option *option, struct in_addr *inp ) { if ( option ) *inp = option->data.in; } /** * Print DHCP string option value into buffer * * @v buf Buffer into which to write the string * @v size Size of buffer * @v option DHCP option, or NULL * @ret len Length of formatted string * * DHCP option strings are stored without a NUL terminator. This * function provides a convenient way to extract these DHCP strings * into standard C strings. It is permitted to call dhcp_snprintf() * with @c option set to NULL; in this case the buffer will be filled * with an empty string. * * The usual snprintf() semantics apply with regard to buffer size, * return value when the buffer is too small, etc. */ int dhcp_snprintf ( char *buf, size_t size, struct dhcp_option *option ) { size_t len; char *content = ""; if ( option ) { /* Shrink buffer size so that it is only just large * enough to contain the option data. snprintf() will * take care of everything else (inserting the NUL etc.) */ len = ( option->len + 1 ); if ( len < size ) size = len; content = option->data.string; } return snprintf ( buf, size, "%s", content ); } /** * Calculate length of a normal DHCP option * * @v option DHCP option * @ret len Length (including tag and length field) * * @c option may not be a @c DHCP_PAD or @c DHCP_END option. */ static inline unsigned int dhcp_option_len ( struct dhcp_option *option ) { assert ( option->tag != DHCP_PAD ); assert ( option->tag != DHCP_END ); return ( option->len + DHCP_OPTION_HEADER_LEN ); } /** * Calculate length of any DHCP option * * @v option DHCP option * @ret len Length (including tag and length field) */ static inline unsigned int dhcp_any_option_len ( struct dhcp_option *option ) { if ( ( option->tag == DHCP_END ) || ( option->tag == DHCP_PAD ) ) { return 1; } else { return dhcp_option_len ( option ); } } /** * Find DHCP option within DHCP options block, and its encapsulator (if any) * * @v options DHCP options block * @v tag DHCP option tag to search for * @ret encapsulator Encapsulating DHCP option * @ret option DHCP option, or NULL if not found * * Searches for the DHCP option matching the specified tag within the * DHCP option block. Encapsulated options may be searched for by * using DHCP_ENCAP_OPT() to construct the tag value. * * If the option is encapsulated, and @c encapsulator is non-NULL, it * will be filled in with a pointer to the encapsulating option. * * This routine is designed to be paranoid. It does not assume that * the option data is well-formatted, and so must guard against flaws * such as options missing a @c DHCP_END terminator, or options whose * length would take them beyond the end of the data block. */ static struct dhcp_option * find_dhcp_option_with_encap ( struct dhcp_option_block *options, unsigned int tag, struct dhcp_option **encapsulator ) { unsigned int original_tag __attribute__ (( unused )) = tag; struct dhcp_option *option = options->data; ssize_t remaining = options->len; unsigned int option_len; while ( remaining ) { /* Calculate length of this option. Abort processing * if the length is malformed (i.e. takes us beyond * the end of the data block). */ option_len = dhcp_any_option_len ( option ); remaining -= option_len; if ( remaining < 0 ) break; /* Check for matching tag */ if ( option->tag == tag ) { DBG ( "Found DHCP option %s (length %d) in block %p\n", dhcp_tag_name ( original_tag ), option->len, options ); return option; } /* Check for explicit end marker */ if ( option->tag == DHCP_END ) break; /* Check for start of matching encapsulation block */ if ( DHCP_IS_ENCAP_OPT ( tag ) && ( option->tag == DHCP_ENCAPSULATOR ( tag ) ) ) { if ( encapsulator ) *encapsulator = option; /* Continue search within encapsulated option block */ tag = DHCP_ENCAPSULATED ( tag ); remaining = option->len; option = ( void * ) &option->data; continue; } option = ( ( ( void * ) option ) + option_len ); } return NULL; } /** * Find DHCP option within DHCP options block * * @v options DHCP options block, or NULL * @v tag DHCP option tag to search for * @ret option DHCP option, or NULL if not found * * Searches for the DHCP option matching the specified tag within the * DHCP option block. Encapsulated options may be searched for by * using DHCP_ENCAP_OPT() to construct the tag value. * * If @c options is NULL, all registered option blocks will be * searched. Where multiple option blocks contain the same DHCP * option, the option from the highest-priority block will be * returned. (Priority of an options block is determined by the value * of the @c DHCP_EB_PRIORITY option within the block, if present; the * default priority is zero). */ struct dhcp_option * find_dhcp_option ( struct dhcp_option_block *options, unsigned int tag ) { struct dhcp_option *option; if ( options ) { return find_dhcp_option_with_encap ( options, tag, NULL ); } else { list_for_each_entry ( options, &option_blocks, list ) { if ( ( option = find_dhcp_option ( options, tag ) ) ) return option; } return NULL; } } /** * Register DHCP option block * * @v options DHCP option block * * Register a block of DHCP options. */ void register_dhcp_options ( struct dhcp_option_block *options ) { struct dhcp_option_block *existing; /* Determine priority of new block */ options->priority = find_dhcp_num_option ( options, DHCP_EB_PRIORITY ); DBG ( "Registering DHCP options block %p with priority %d\n", options, options->priority ); /* Insert after any existing blocks which have a higher priority */ list_for_each_entry ( existing, &option_blocks, list ) { if ( options->priority > existing->priority ) break; } list_add_tail ( &options->list, &existing->list ); } /** * Unregister DHCP option block * * @v options DHCP option block */ void unregister_dhcp_options ( struct dhcp_option_block *options ) { list_del ( &options->list ); } /** * Initialise empty block of DHCP options * * @v options Uninitialised DHCP option block * @v data Memory for DHCP option data * @v max_len Length of memory for DHCP option data * * Populates the DHCP option data with a single @c DHCP_END option and * fills in the fields of the @c dhcp_option_block structure. */ void init_dhcp_options ( struct dhcp_option_block *options, void *data, size_t max_len ) { struct dhcp_option *option; options->data = data; options->max_len = max_len; option = options->data; option->tag = DHCP_END; options->len = 1; DBG ( "DHCP options block %p initialised (data %p max_len %#zx)\n", options, options->data, options->max_len ); } /** * Allocate space for a block of DHCP options * * @v max_len Maximum length of option block * @ret options DHCP option block, or NULL * * Creates a new DHCP option block and populates it with an empty * options list. This call does not register the options block. */ struct dhcp_option_block * alloc_dhcp_options ( size_t max_len ) { struct dhcp_option_block *options; options = malloc ( sizeof ( *options ) + max_len ); if ( options ) { init_dhcp_options ( options, ( (void *) options + sizeof ( *options ) ), max_len ); } return options; } /** * Free DHCP options block * * @v options DHCP option block */ void free_dhcp_options ( struct dhcp_option_block *options ) { free ( options ); } /** * Resize a DHCP option * * @v options DHCP option block * @v option DHCP option to resize * @v encapsulator Encapsulating option (or NULL) * @v old_len Old length (including header) * @v new_len New length (including header) * @ret rc Return status code */ static int resize_dhcp_option ( struct dhcp_option_block *options, struct dhcp_option *option, struct dhcp_option *encapsulator, size_t old_len, size_t new_len ) { void *source = ( ( ( void * ) option ) + old_len ); void *dest = ( ( ( void * ) option ) + new_len ); void *end = ( options->data + options->max_len ); ssize_t delta = ( new_len - old_len ); size_t new_options_len; size_t new_encapsulator_len; /* Check for sufficient space, and update length fields */ if ( new_len > DHCP_MAX_LEN ) return -ENOMEM; new_options_len = ( options->len + delta ); if ( new_options_len > options->max_len ) return -ENOMEM; if ( encapsulator ) { new_encapsulator_len = ( encapsulator->len + delta ); if ( new_encapsulator_len > DHCP_MAX_LEN ) return -ENOMEM; encapsulator->len = new_encapsulator_len; } options->len = new_options_len; /* Move remainder of option data */ memmove ( dest, source, ( end - dest ) ); return 0; } /** * Set value of DHCP option * * @v options DHCP option block * @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 value of a DHCP option within the options block. The * option may or may not already exist. Encapsulators will be created * (and deleted) as necessary. * * This call may fail due to insufficient space in the options block. * If it does fail, and the option existed previously, the option will * be left with its original value. */ struct dhcp_option * set_dhcp_option ( struct dhcp_option_block *options, unsigned int tag, const void *data, size_t len ) { static const uint8_t empty_encapsulator[] = { DHCP_END }; struct dhcp_option *option; void *insertion_point = options->data; struct dhcp_option *encapsulator = NULL; unsigned int encap_tag = DHCP_ENCAPSULATOR ( tag ); size_t old_len = 0; size_t new_len = ( len ? ( len + DHCP_OPTION_HEADER_LEN ) : 0 ); /* Find old instance of this option, if any */ option = find_dhcp_option_with_encap ( options, tag, &encapsulator ); if ( option ) { old_len = dhcp_option_len ( option ); DBG ( "Resizing DHCP option %s from length %d to %d in block " "%p\n", dhcp_tag_name (tag), option->len, len, options ); } else { old_len = 0; DBG ( "Creating DHCP option %s (length %d) in block %p\n", dhcp_tag_name ( tag ), len, options ); } /* Ensure that encapsulator exists, if required */ if ( DHCP_IS_ENCAP_OPT ( tag ) ) { if ( ! encapsulator ) encapsulator = set_dhcp_option ( options, encap_tag, empty_encapsulator, sizeof ( empty_encapsulator) ); if ( ! encapsulator ) return NULL; insertion_point = &encapsulator->data; } /* Create new option if necessary */ if ( ! option ) option = insertion_point; /* Resize option to fit new data */ if ( resize_dhcp_option ( options, option, encapsulator, old_len, new_len ) != 0 ) return NULL; /* Copy new data into option, if applicable */ if ( len ) { option->tag = tag; option->len = len; memcpy ( &option->data, data, len ); } /* Delete encapsulator if there's nothing else left in it */ if ( encapsulator && ( encapsulator->len <= 1 ) ) set_dhcp_option ( options, encap_tag, NULL, 0 ); return option; } /** * Find DHCP option within all registered DHCP options blocks * * @v tag DHCP option tag to search for * @ret option DHCP option, or NULL if not found * * This function exists merely as a notational shorthand for * find_dhcp_option() with @c options set to NULL. */ struct dhcp_option * find_global_dhcp_option ( unsigned int tag ) { return find_dhcp_option ( NULL, tag ); } /** * Find DHCP numerical option, and return its value * * @v options DHCP options block * @v tag DHCP option tag to search for * @ret value Numerical value of the option, or 0 if not found * * This function exists merely as a notational shorthand for a call to * find_dhcp_option() followed by a call to dhcp_num_option(). It is * not possible to distinguish between the cases "option not found" * and "option has a value of zero" using this function; if this * matters to you then issue the two constituent calls directly and * check that find_dhcp_option() returns a non-NULL value. */ unsigned long find_dhcp_num_option ( struct dhcp_option_block *options, unsigned int tag ) { return dhcp_num_option ( find_dhcp_option ( options, tag ) ); } /** * Find DHCP numerical option, and return its value * * @v tag DHCP option tag to search for * @ret value Numerical value of the option, or 0 if not found * * This function exists merely as a notational shorthand for a call to * find_global_dhcp_option() followed by a call to dhcp_num_option(). * It is not possible to distinguish between the cases "option not * found" and "option has a value of zero" using this function; if * this matters to you then issue the two constituent calls directly * and check that find_global_dhcp_option() returns a non-NULL value. */ unsigned long find_global_dhcp_num_option ( unsigned int tag ) { return dhcp_num_option ( find_global_dhcp_option ( tag ) ); } /** * Find DHCP IPv4-address option, and return its value * * @v options DHCP options block * @v tag DHCP option tag to search for * @v inp IPv4 address to fill in * @ret value Numerical value of the option, or 0 if not found * * This function exists merely as a notational shorthand for a call to * find_dhcp_option() followed by a call to dhcp_ipv4_option(). It is * not possible to distinguish between the cases "option not found" * and "option has a value of 0.0.0.0" using this function; if this * matters to you then issue the two constituent calls directly and * check that find_dhcp_option() returns a non-NULL value. */ void find_dhcp_ipv4_option ( struct dhcp_option_block *options, unsigned int tag, struct in_addr *inp ) { dhcp_ipv4_option ( find_dhcp_option ( options, tag ), inp ); } /** * Find DHCP IPv4-address option, and return its value * * @v options DHCP options block * @v tag DHCP option tag to search for * @v inp IPv4 address to fill in * @ret value Numerical value of the option, or 0 if not found * * This function exists merely as a notational shorthand for a call to * find_dhcp_option() followed by a call to dhcp_ipv4_option(). It is * not possible to distinguish between the cases "option not found" * and "option has a value of 0.0.0.0" using this function; if this * matters to you then issue the two constituent calls directly and * check that find_dhcp_option() returns a non-NULL value. */ void find_global_dhcp_ipv4_option ( unsigned int tag, struct in_addr *inp ) { dhcp_ipv4_option ( find_global_dhcp_option ( tag ), inp ); } /** * Delete DHCP option * * @v options DHCP options block * @v tag DHCP option tag * * This function exists merely as a notational shorthand for a call to * set_dhcp_option() with @c len set to zero. */ void delete_dhcp_option ( struct dhcp_option_block *options, unsigned int tag ) { set_dhcp_option ( options, tag, NULL, 0 ); }