src/net/dhcpopts.c

   1 /*
   2  * Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2 of the
   7  * License, or any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 FILE_LICENCE ( GPL2_OR_LATER );
  20
  21 #include <stdint.h>
  22 #include <stdlib.h>
  23 #include <stdio.h>
  24 #include <errno.h>
  25 #include <string.h>
  26 #include <gpxe/dhcp.h>
  27 #include <gpxe/dhcpopts.h>
  28
  29 /** @file
  30  *
  31  * DHCP options
  32  *
  33  */
  34
  35 /**
  36  * Obtain printable version of a DHCP option tag
  37  *
  38  * @v tag               DHCP option tag
  39  * @ret name            String representation of the tag
  40  *
  41  */
  42 static inline char * dhcp_tag_name ( unsigned int tag ) {
  43         static char name[8];
  44
  45         if ( DHCP_IS_ENCAP_OPT ( tag ) ) {
  46                 snprintf ( name, sizeof ( name ), "%d.%d",
  47                            DHCP_ENCAPSULATOR ( tag ),
  48                            DHCP_ENCAPSULATED ( tag ) );
  49         } else {
  50                 snprintf ( name, sizeof ( name ), "%d", tag );
  51         }
  52         return name;
  53 }
  54
  55 /**
  56  * Get pointer to DHCP option
  57  *
  58  * @v options           DHCP options block
  59  * @v offset            Offset within options block
  60  * @ret option          DHCP option
  61  */
  62 static inline __attribute__ (( always_inline )) struct dhcp_option *
  63 dhcp_option ( struct dhcp_options *options, unsigned int offset ) {
  64         return ( ( struct dhcp_option * ) ( options->data + offset ) );
  65 }
  66
  67 /**
  68  * Get offset of a DHCP option
  69  *
  70  * @v options           DHCP options block
  71  * @v option            DHCP option
  72  * @ret offset          Offset within options block
  73  */
  74 static inline __attribute__ (( always_inline )) int
  75 dhcp_option_offset ( struct dhcp_options *options,
  76                      struct dhcp_option *option ) {
  77         return ( ( ( void * ) option ) - options->data );
  78 }
  79
  80 /**
  81  * Calculate length of any DHCP option
  82  *
  83  * @v option            DHCP option
  84  * @ret len             Length (including tag and length field)
  85  */
  86 static unsigned int dhcp_option_len ( struct dhcp_option *option ) {
  87         if ( ( option->tag == DHCP_END ) || ( option->tag == DHCP_PAD ) ) {
  88                 return 1;
  89         } else {
  90                 return ( option->len + DHCP_OPTION_HEADER_LEN );
  91         }
  92 }
  93
  94 /**
  95  * Find DHCP option within DHCP options block, and its encapsulator (if any)
  96  *
  97  * @v options           DHCP options block
  98  * @v tag               DHCP option tag to search for
  99  * @ret encap_offset    Offset of encapsulating DHCP option
 100  * @ret offset          Offset of DHCP option, or negative error
 101  *
 102  * Searches for the DHCP option matching the specified tag within the
 103  * DHCP option block.  Encapsulated options may be searched for by
 104  * using DHCP_ENCAP_OPT() to construct the tag value.
 105  *
 106  * If the option is encapsulated, and @c encapsulator is non-NULL, it
 107  * will be filled in with the offset of the encapsulating option.
 108  *
 109  * This routine is designed to be paranoid.  It does not assume that
 110  * the option data is well-formatted, and so must guard against flaws
 111  * such as options missing a @c DHCP_END terminator, or options whose
 112  * length would take them beyond the end of the data block.
 113  */
 114 static int find_dhcp_option_with_encap ( struct dhcp_options *options,
 115                                          unsigned int tag,
 116                                          int *encap_offset ) {
 117         unsigned int original_tag __attribute__ (( unused )) = tag;
 118         struct dhcp_option *option;
 119         int offset = 0;
 120         ssize_t remaining = options->len;
 121         unsigned int option_len;
 122
 123         /* Sanity check */
 124         if ( tag == DHCP_PAD )
 125                 return -ENOENT;
 126
 127         /* Search for option */
 128         while ( remaining ) {
 129                 /* Calculate length of this option.  Abort processing
 130                  * if the length is malformed (i.e. takes us beyond
 131                  * the end of the data block).
 132                  */
 133                 option = dhcp_option ( options, offset );
 134                 option_len = dhcp_option_len ( option );
 135                 remaining -= option_len;
 136                 if ( remaining < 0 )
 137                         break;
 138                 /* Check for explicit end marker */
 139                 if ( option->tag == DHCP_END )
 140                         break;
 141                 /* Check for matching tag */
 142                 if ( option->tag == tag ) {
 143                         DBGC ( options, "DHCPOPT %p found %s (length %d)\n",
 144                                options, dhcp_tag_name ( original_tag ),
 145                                option_len );
 146                         return offset;
 147                 }
 148                 /* Check for start of matching encapsulation block */
 149                 if ( DHCP_IS_ENCAP_OPT ( tag ) &&
 150                      ( option->tag == DHCP_ENCAPSULATOR ( tag ) ) ) {
 151                         if ( encap_offset )
 152                                 *encap_offset = offset;
 153                         /* Continue search within encapsulated option block */
 154                         tag = DHCP_ENCAPSULATED ( tag );
 155                         remaining = option_len;
 156                         offset += DHCP_OPTION_HEADER_LEN;
 157                         continue;
 158                 }
 159                 offset += option_len;
 160         }
 161
 162         return -ENOENT;
 163 }
 164
 165 /**
 166  * Resize a DHCP option
 167  *
 168  * @v options           DHCP option block
 169  * @v offset            Offset of option to resize
 170  * @v encap_offset      Offset of encapsulating offset (or -ve for none)
 171  * @v old_len           Old length (including header)
 172  * @v new_len           New length (including header)
 173  * @v can_realloc       Can reallocate options data if necessary
 174  * @ret rc              Return status code
 175  */
 176 static int resize_dhcp_option ( struct dhcp_options *options,
 177                                 int offset, int encap_offset,
 178                                 size_t old_len, size_t new_len,
 179                                 int can_realloc ) {
 180         struct dhcp_option *encapsulator;
 181         struct dhcp_option *option;
 182         ssize_t delta = ( new_len - old_len );
 183         size_t new_options_len;
 184         size_t new_encapsulator_len;
 185         void *new_data;
 186         void *source;
 187         void *dest;
 188         void *end;
 189
 190         /* Check for sufficient space, and update length fields */
 191         if ( new_len > DHCP_MAX_LEN ) {
 192                 DBGC ( options, "DHCPOPT %p overlength option\n", options );
 193                 return -ENOSPC;
 194         }
 195         new_options_len = ( options->len + delta );
 196         if ( new_options_len > options->max_len ) {
 197                 /* Reallocate options block if allowed to do so. */
 198                 if ( can_realloc ) {
 199                         new_data = realloc ( options->data, new_options_len );
 200                         if ( ! new_data ) {
 201                                 DBGC ( options, "DHCPOPT %p could not "
 202                                        "reallocate to %zd bytes\n", options,
 203                                        new_options_len );
 204                                 return -ENOMEM;
 205                         }
 206                         options->data = new_data;
 207                         options->max_len = new_options_len;
 208                 } else {
 209                         DBGC ( options, "DHCPOPT %p out of space\n", options );
 210                         return -ENOMEM;
 211                 }
 212         }
 213         if ( encap_offset >= 0 ) {
 214                 encapsulator = dhcp_option ( options, encap_offset );
 215                 new_encapsulator_len = ( encapsulator->len + delta );
 216                 if ( new_encapsulator_len > DHCP_MAX_LEN ) {
 217                         DBGC ( options, "DHCPOPT %p overlength encapsulator\n",
 218                                options );
 219                         return -ENOSPC;
 220                 }
 221                 encapsulator->len = new_encapsulator_len;
 222         }
 223         options->len = new_options_len;
 224
 225         /* Move remainder of option data */
 226         option = dhcp_option ( options, offset );
 227         source = ( ( ( void * ) option ) + old_len );
 228         dest = ( ( ( void * ) option ) + new_len );
 229         end = ( options->data + options->max_len );
 230         memmove ( dest, source, ( end - dest ) );
 231
 232         return 0;
 233 }
 234
 235 /**
 236  * Set value of DHCP option
 237  *
 238  * @v options           DHCP option block
 239  * @v tag               DHCP option tag
 240  * @v data              New value for DHCP option
 241  * @v len               Length of value, in bytes
 242  * @v can_realloc       Can reallocate options data if necessary
 243  * @ret offset          Offset of DHCP option, or negative error
 244  *
 245  * Sets the value of a DHCP option within the options block.  The
 246  * option may or may not already exist.  Encapsulators will be created
 247  * (and deleted) as necessary.
 248  *
 249  * This call may fail due to insufficient space in the options block.
 250  * If it does fail, and the option existed previously, the option will
 251  * be left with its original value.
 252  */
 253 static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
 254                              const void *data, size_t len,
 255                              int can_realloc ) {
 256         static const uint8_t empty_encapsulator[] = { DHCP_END };
 257         int offset;
 258         int encap_offset = -1;
 259         int creation_offset = 0;
 260         struct dhcp_option *option;
 261         unsigned int encap_tag = DHCP_ENCAPSULATOR ( tag );
 262         size_t old_len = 0;
 263         size_t new_len = ( len ? ( len + DHCP_OPTION_HEADER_LEN ) : 0 );
 264         int rc;
 265
 266         /* Sanity check */
 267         if ( tag == DHCP_PAD )
 268                 return -ENOTTY;
 269
 270         /* Find old instance of this option, if any */
 271         offset = find_dhcp_option_with_encap ( options, tag, &encap_offset );
 272         if ( offset >= 0 ) {
 273                 old_len = dhcp_option_len ( dhcp_option ( options, offset ) );
 274                 DBGC ( options, "DHCPOPT %p resizing %s from %zd to %zd\n",
 275                        options, dhcp_tag_name ( tag ), old_len, new_len );
 276         } else {
 277                 DBGC ( options, "DHCPOPT %p creating %s (length %zd)\n",
 278                        options, dhcp_tag_name ( tag ), new_len );
 279         }
 280
 281         /* Ensure that encapsulator exists, if required */
 282         if ( encap_tag ) {
 283                 if ( encap_offset < 0 )
 284                         encap_offset = set_dhcp_option ( options, encap_tag,
 285                                                          empty_encapsulator, 1,
 286                                                          can_realloc );
 287                 if ( encap_offset < 0 )
 288                         return encap_offset;
 289                 creation_offset = ( encap_offset + DHCP_OPTION_HEADER_LEN );
 290         }
 291
 292         /* Create new option if necessary */
 293         if ( offset < 0 )
 294                 offset = creation_offset;
 295
 296         /* Resize option to fit new data */
 297         if ( ( rc = resize_dhcp_option ( options, offset, encap_offset,
 298                                          old_len, new_len,
 299                                          can_realloc ) ) != 0 )
 300                 return rc;
 301
 302         /* Copy new data into option, if applicable */
 303         if ( len ) {
 304                 option = dhcp_option ( options, offset );
 305                 option->tag = tag;
 306                 option->len = len;
 307                 memcpy ( &option->data, data, len );
 308         }
 309
 310         /* Delete encapsulator if there's nothing else left in it */
 311         if ( encap_offset >= 0 ) {
 312                 option = dhcp_option ( options, encap_offset );
 313                 if ( option->len <= 1 )
 314                         set_dhcp_option ( options, encap_tag, NULL, 0, 0 );
 315         }
 316
 317         return offset;
 318 }
 319
 320 /**
 321  * Store value of DHCP option setting
 322  *
 323  * @v options           DHCP option block
 324  * @v tag               Setting tag number
 325  * @v data              Setting data, or NULL to clear setting
 326  * @v len               Length of setting data
 327  * @ret rc              Return status code
 328  */
 329 int dhcpopt_store ( struct dhcp_options *options, unsigned int tag,
 330                     const void *data, size_t len ) {
 331         int offset;
 332
 333         offset = set_dhcp_option ( options, tag, data, len, 0 );
 334         if ( offset < 0 )
 335                 return offset;
 336         return 0;
 337 }
 338
 339 /**
 340  * Store value of DHCP option setting, extending options block if necessary
 341  *
 342  * @v options           DHCP option block
 343  * @v tag               Setting tag number
 344  * @v data              Setting data, or NULL to clear setting
 345  * @v len               Length of setting data
 346  * @ret rc              Return status code
 347  */
 348 int dhcpopt_extensible_store ( struct dhcp_options *options, unsigned int tag,
 349                                const void *data, size_t len ) {
 350         int offset;
 351
 352         offset = set_dhcp_option ( options, tag, data, len, 1 );
 353         if ( offset < 0 )
 354                 return offset;
 355         return 0;
 356 }
 357
 358 /**
 359  * Fetch value of DHCP option setting
 360  *
 361  * @v options           DHCP option block
 362  * @v tag               Setting tag number
 363  * @v data              Buffer to fill with setting data
 364  * @v len               Length of buffer
 365  * @ret len             Length of setting data, or negative error
 366  */
 367 int dhcpopt_fetch ( struct dhcp_options *options, unsigned int tag,
 368                     void *data, size_t len ) {
 369         int offset;
 370         struct dhcp_option *option;
 371         size_t option_len;
 372
 373         offset = find_dhcp_option_with_encap ( options, tag, NULL );
 374         if ( offset < 0 )
 375                 return offset;
 376
 377         option = dhcp_option ( options, offset );
 378         option_len = option->len;
 379         if ( len > option_len )
 380                 len = option_len;
 381         memcpy ( data, option->data, len );
 382
 383         return option_len;
 384 }
 385
 386 /**
 387  * Recalculate length of DHCP options block
 388  *
 389  * @v options           Uninitialised DHCP option block
 390  *
 391  * The "used length" field will be updated based on scanning through
 392  * the block to find the end of the options.
 393  */
 394 static void dhcpopt_update_len ( struct dhcp_options *options ) {
 395         struct dhcp_option *option;
 396         int offset = 0;
 397         ssize_t remaining = options->max_len;
 398         unsigned int option_len;
 399
 400         /* Find last non-pad option */
 401         options->len = 0;
 402         while ( remaining ) {
 403                 option = dhcp_option ( options, offset );
 404                 option_len = dhcp_option_len ( option );
 405                 remaining -= option_len;
 406                 if ( remaining < 0 )
 407                         break;
 408                 offset += option_len;
 409                 if ( option->tag != DHCP_PAD )
 410                         options->len = offset;
 411         }
 412 }
 413
 414 /**
 415  * Initialise prepopulated block of DHCP options
 416  *
 417  * @v options           Uninitialised DHCP option block
 418  * @v data              Memory for DHCP option data
 419  * @v max_len           Length of memory for DHCP option data
 420  *
 421  * The memory content must already be filled with valid DHCP options.
 422  * A zeroed block counts as a block of valid DHCP options.
 423  */
 424 void dhcpopt_init ( struct dhcp_options *options, void *data,
 425                     size_t max_len ) {
 426
 427         /* Fill in fields */
 428         options->data = data;
 429         options->max_len = max_len;
 430
 431         /* Update length */
 432         dhcpopt_update_len ( options );
 433
 434         DBGC ( options, "DHCPOPT %p created (data %p len %#zx max_len %#zx)\n",
 435                options, options->data, options->len, options->max_len );
 436 }