gpxe/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 encap_offset 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                         if ( tag == DHCP_END )
 141                                 /* Special case where the caller is interested
 142                                  * in whether we have this marker or not.
 143                                  */
 144                                 return offset;
 145                         else
 146                                 break;
 147                 }
 148                 /* Check for matching tag */
 149                 if ( option->tag == tag ) {
 150                         DBGC ( options, "DHCPOPT %p found %s (length %d)\n",
 151                                options, dhcp_tag_name ( original_tag ),
 152                                option_len );
 153                         return offset;
 154                 }
 155                 /* Check for start of matching encapsulation block */
 156                 if ( DHCP_IS_ENCAP_OPT ( tag ) &&
 157                      ( option->tag == DHCP_ENCAPSULATOR ( tag ) ) ) {
 158                         if ( encap_offset )
 159                                 *encap_offset = offset;
 160                         /* Continue search within encapsulated option block */
 161                         tag = DHCP_ENCAPSULATED ( tag );
 162                         remaining = option_len;
 163                         offset += DHCP_OPTION_HEADER_LEN;
 164                         continue;
 165                 }
 166                 offset += option_len;
 167         }
 168
 169         return -ENOENT;
 170 }
 171
 172 /**
 173  * Resize a DHCP option
 174  *
 175  * @v options           DHCP option block
 176  * @v offset            Offset of option to resize
 177  * @v encap_offset      Offset of encapsulating offset (or -ve for none)
 178  * @v old_len           Old length (including header)
 179  * @v new_len           New length (including header)
 180  * @v can_realloc       Can reallocate options data if necessary
 181  * @ret rc              Return status code
 182  */
 183 static int resize_dhcp_option ( struct dhcp_options *options,
 184                                 int offset, int encap_offset,
 185                                 size_t old_len, size_t new_len,
 186                                 int can_realloc ) {
 187         struct dhcp_option *encapsulator;
 188         struct dhcp_option *option;
 189         ssize_t delta = ( new_len - old_len );
 190         size_t new_options_len;
 191         size_t new_encapsulator_len;
 192         void *new_data;
 193         void *source;
 194         void *dest;
 195         void *end;
 196
 197         /* Check for sufficient space, and update length fields */
 198         if ( new_len > DHCP_MAX_LEN ) {
 199                 DBGC ( options, "DHCPOPT %p overlength option\n", options );
 200                 return -ENOSPC;
 201         }
 202         new_options_len = ( options->len + delta );
 203         if ( new_options_len > options->max_len ) {
 204                 /* Reallocate options block if allowed to do so. */
 205                 if ( can_realloc ) {
 206                         new_data = realloc ( options->data, new_options_len );
 207                         if ( ! new_data ) {
 208                                 DBGC ( options, "DHCPOPT %p could not "
 209                                        "reallocate to %zd bytes\n", options,
 210                                        new_options_len );
 211                                 return -ENOMEM;
 212                         }
 213                         options->data = new_data;
 214                         options->max_len = new_options_len;
 215                 } else {
 216                         DBGC ( options, "DHCPOPT %p out of space\n", options );
 217                         return -ENOMEM;
 218                 }
 219         }
 220         if ( encap_offset >= 0 ) {
 221                 encapsulator = dhcp_option ( options, encap_offset );
 222                 new_encapsulator_len = ( encapsulator->len + delta );
 223                 if ( new_encapsulator_len > DHCP_MAX_LEN ) {
 224                         DBGC ( options, "DHCPOPT %p overlength encapsulator\n",
 225                                options );
 226                         return -ENOSPC;
 227                 }
 228                 encapsulator->len = new_encapsulator_len;
 229         }
 230         options->len = new_options_len;
 231
 232         /* Move remainder of option data */
 233         option = dhcp_option ( options, offset );
 234         source = ( ( ( void * ) option ) + old_len );
 235         dest = ( ( ( void * ) option ) + new_len );
 236         end = ( options->data + options->max_len );
 237         memmove ( dest, source, ( end - dest ) );
 238
 239         return 0;
 240 }
 241
 242 /**
 243  * Set value of DHCP option
 244  *
 245  * @v options           DHCP option block
 246  * @v tag               DHCP option tag
 247  * @v data              New value for DHCP option
 248  * @v len               Length of value, in bytes
 249  * @v can_realloc       Can reallocate options data if necessary
 250  * @ret offset          Offset of DHCP option, or negative error
 251  *
 252  * Sets the value of a DHCP option within the options block.  The
 253  * option may or may not already exist.  Encapsulators will be created
 254  * (and deleted) as necessary.
 255  *
 256  * This call may fail due to insufficient space in the options block.
 257  * If it does fail, and the option existed previously, the option will
 258  * be left with its original value.
 259  */
 260 static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
 261                              const void *data, size_t len,
 262                              int can_realloc ) {
 263         static const uint8_t empty_encapsulator[] = { DHCP_END };
 264         int offset;
 265         int encap_offset = -1;
 266         int creation_offset;
 267         struct dhcp_option *option;
 268         unsigned int encap_tag = DHCP_ENCAPSULATOR ( tag );
 269         size_t old_len = 0;
 270         size_t new_len = ( len ? ( len + DHCP_OPTION_HEADER_LEN ) : 0 );
 271         int rc;
 272
 273         /* Sanity check */
 274         if ( tag == DHCP_PAD )
 275                 return -ENOTTY;
 276
 277         creation_offset = find_dhcp_option_with_encap ( options, DHCP_END,
 278                                                         NULL );
 279         if ( creation_offset < 0 )
 280                 creation_offset = options->len;
 281         /* Find old instance of this option, if any */
 282         offset = find_dhcp_option_with_encap ( options, tag, &encap_offset );
 283         if ( offset >= 0 ) {
 284                 old_len = dhcp_option_len ( dhcp_option ( options, offset ) );
 285                 DBGC ( options, "DHCPOPT %p resizing %s from %zd to %zd\n",
 286                        options, dhcp_tag_name ( tag ), old_len, new_len );
 287         } else {
 288                 DBGC ( options, "DHCPOPT %p creating %s (length %zd)\n",
 289                        options, dhcp_tag_name ( tag ), new_len );
 290         }
 291
 292         /* Ensure that encapsulator exists, if required */
 293         if ( encap_tag ) {
 294                 if ( encap_offset < 0 )
 295                         encap_offset = set_dhcp_option ( options, encap_tag,
 296                                                          empty_encapsulator, 1,
 297                                                          can_realloc );
 298                 if ( encap_offset < 0 )
 299                         return encap_offset;
 300                 creation_offset = ( encap_offset + DHCP_OPTION_HEADER_LEN );
 301         }
 302
 303         /* Create new option if necessary */
 304         if ( offset < 0 )
 305                 offset = creation_offset;
 306
 307         /* Resize option to fit new data */
 308         if ( ( rc = resize_dhcp_option ( options, offset, encap_offset,
 309                                          old_len, new_len,
 310                                          can_realloc ) ) != 0 )
 311                 return rc;
 312
 313         /* Copy new data into option, if applicable */
 314         if ( len ) {
 315                 option = dhcp_option ( options, offset );
 316                 option->tag = tag;
 317                 option->len = len;
 318                 memcpy ( &option->data, data, len );
 319         }
 320
 321         /* Delete encapsulator if there's nothing else left in it */
 322         if ( encap_offset >= 0 ) {
 323                 option = dhcp_option ( options, encap_offset );
 324                 if ( option->len <= 1 )
 325                         set_dhcp_option ( options, encap_tag, NULL, 0, 0 );
 326         }
 327
 328         return offset;
 329 }
 330
 331 /**
 332  * Store value of DHCP option setting
 333  *
 334  * @v options           DHCP option block
 335  * @v tag               Setting tag number
 336  * @v data              Setting data, or NULL to clear setting
 337  * @v len               Length of setting data
 338  * @ret rc              Return status code
 339  */
 340 int dhcpopt_store ( struct dhcp_options *options, unsigned int tag,
 341                     const void *data, size_t len ) {
 342         int offset;
 343
 344         offset = set_dhcp_option ( options, tag, data, len, 0 );
 345         if ( offset < 0 )
 346                 return offset;
 347         return 0;
 348 }
 349
 350 /**
 351  * Store value of DHCP option setting, extending options block if necessary
 352  *
 353  * @v options           DHCP option block
 354  * @v tag               Setting tag number
 355  * @v data              Setting data, or NULL to clear setting
 356  * @v len               Length of setting data
 357  * @ret rc              Return status code
 358  */
 359 int dhcpopt_extensible_store ( struct dhcp_options *options, unsigned int tag,
 360                                const void *data, size_t len ) {
 361         int offset;
 362
 363         offset = set_dhcp_option ( options, tag, data, len, 1 );
 364         if ( offset < 0 )
 365                 return offset;
 366         return 0;
 367 }
 368
 369 /**
 370  * Fetch value of DHCP option setting
 371  *
 372  * @v options           DHCP option block
 373  * @v tag               Setting tag number
 374  * @v data              Buffer to fill with setting data
 375  * @v len               Length of buffer
 376  * @ret len             Length of setting data, or negative error
 377  */
 378 int dhcpopt_fetch ( struct dhcp_options *options, unsigned int tag,
 379                     void *data, size_t len ) {
 380         int offset;
 381         struct dhcp_option *option;
 382         size_t option_len;
 383
 384         offset = find_dhcp_option_with_encap ( options, tag, NULL );
 385         if ( offset < 0 )
 386                 return offset;
 387
 388         option = dhcp_option ( options, offset );
 389         option_len = option->len;
 390         if ( len > option_len )
 391                 len = option_len;
 392         memcpy ( data, option->data, len );
 393
 394         return option_len;
 395 }
 396
 397 /**
 398  * Recalculate length of DHCP options block
 399  *
 400  * @v options           Uninitialised DHCP option block
 401  *
 402  * The "used length" field will be updated based on scanning through
 403  * the block to find the end of the options.
 404  */
 405 static void dhcpopt_update_len ( struct dhcp_options *options ) {
 406         struct dhcp_option *option;
 407         int offset = 0;
 408         ssize_t remaining = options->max_len;
 409         unsigned int option_len;
 410
 411         /* Find last non-pad option */
 412         options->len = 0;
 413         while ( remaining ) {
 414                 option = dhcp_option ( options, offset );
 415                 option_len = dhcp_option_len ( option );
 416                 remaining -= option_len;
 417                 if ( remaining < 0 )
 418                         break;
 419                 offset += option_len;
 420                 if ( option->tag != DHCP_PAD )
 421                         options->len = offset;
 422         }
 423 }
 424
 425 /**
 426  * Initialise prepopulated block of DHCP options
 427  *
 428  * @v options           Uninitialised DHCP option block
 429  * @v data              Memory for DHCP option data
 430  * @v max_len           Length of memory for DHCP option data
 431  *
 432  * The memory content must already be filled with valid DHCP options.
 433  * A zeroed block counts as a block of valid DHCP options.
 434  */
 435 void dhcpopt_init ( struct dhcp_options *options, void *data,
 436                     size_t max_len ) {
 437
 438         /* Fill in fields */
 439         options->data = data;
 440         options->max_len = max_len;
 441
 442         /* Update length */
 443         dhcpopt_update_len ( options );
 444
 445         DBGC ( options, "DHCPOPT %p created (data %p len %#zx max_len %#zx)\n",
 446                options, options->data, options->len, options->max_len );
 447 }