linux/net/wireless/radiotap.c
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   1/*
   2 * Radiotap parser
   3 *
   4 * Copyright 2007               Andy Green <andy@warmcat.com>
   5 * Copyright 2009               Johannes Berg <johannes@sipsolutions.net>
   6 *
   7 * This program is free software; you can redistribute it and/or modify
   8 * it under the terms of the GNU General Public License version 2 as
   9 * published by the Free Software Foundation.
  10 *
  11 * Alternatively, this software may be distributed under the terms of BSD
  12 * license.
  13 *
  14 * See COPYING for more details.
  15 */
  16
  17#include <linux/kernel.h>
  18#include <linux/export.h>
  19#include <net/cfg80211.h>
  20#include <net/ieee80211_radiotap.h>
  21#include <asm/unaligned.h>
  22
  23/* function prototypes and related defs are in include/net/cfg80211.h */
  24
  25static const struct radiotap_align_size rtap_namespace_sizes[] = {
  26        [IEEE80211_RADIOTAP_TSFT] = { .align = 8, .size = 8, },
  27        [IEEE80211_RADIOTAP_FLAGS] = { .align = 1, .size = 1, },
  28        [IEEE80211_RADIOTAP_RATE] = { .align = 1, .size = 1, },
  29        [IEEE80211_RADIOTAP_CHANNEL] = { .align = 2, .size = 4, },
  30        [IEEE80211_RADIOTAP_FHSS] = { .align = 2, .size = 2, },
  31        [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = { .align = 1, .size = 1, },
  32        [IEEE80211_RADIOTAP_DBM_ANTNOISE] = { .align = 1, .size = 1, },
  33        [IEEE80211_RADIOTAP_LOCK_QUALITY] = { .align = 2, .size = 2, },
  34        [IEEE80211_RADIOTAP_TX_ATTENUATION] = { .align = 2, .size = 2, },
  35        [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = { .align = 2, .size = 2, },
  36        [IEEE80211_RADIOTAP_DBM_TX_POWER] = { .align = 1, .size = 1, },
  37        [IEEE80211_RADIOTAP_ANTENNA] = { .align = 1, .size = 1, },
  38        [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = { .align = 1, .size = 1, },
  39        [IEEE80211_RADIOTAP_DB_ANTNOISE] = { .align = 1, .size = 1, },
  40        [IEEE80211_RADIOTAP_RX_FLAGS] = { .align = 2, .size = 2, },
  41        [IEEE80211_RADIOTAP_TX_FLAGS] = { .align = 2, .size = 2, },
  42        [IEEE80211_RADIOTAP_RTS_RETRIES] = { .align = 1, .size = 1, },
  43        [IEEE80211_RADIOTAP_DATA_RETRIES] = { .align = 1, .size = 1, },
  44        /*
  45         * add more here as they are defined in radiotap.h
  46         */
  47};
  48
  49static const struct ieee80211_radiotap_namespace radiotap_ns = {
  50        .n_bits = ARRAY_SIZE(rtap_namespace_sizes),
  51        .align_size = rtap_namespace_sizes,
  52};
  53
  54/**
  55 * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization
  56 * @iterator: radiotap_iterator to initialize
  57 * @radiotap_header: radiotap header to parse
  58 * @max_length: total length we can parse into (eg, whole packet length)
  59 *
  60 * Returns: 0 or a negative error code if there is a problem.
  61 *
  62 * This function initializes an opaque iterator struct which can then
  63 * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap
  64 * argument which is present in the header.  It knows about extended
  65 * present headers and handles them.
  66 *
  67 * How to use:
  68 * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator
  69 * struct ieee80211_radiotap_iterator (no need to init the struct beforehand)
  70 * checking for a good 0 return code.  Then loop calling
  71 * __ieee80211_radiotap_iterator_next()... it returns either 0,
  72 * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem.
  73 * The iterator's @this_arg member points to the start of the argument
  74 * associated with the current argument index that is present, which can be
  75 * found in the iterator's @this_arg_index member.  This arg index corresponds
  76 * to the IEEE80211_RADIOTAP_... defines.
  77 *
  78 * Radiotap header length:
  79 * You can find the CPU-endian total radiotap header length in
  80 * iterator->max_length after executing ieee80211_radiotap_iterator_init()
  81 * successfully.
  82 *
  83 * Alignment Gotcha:
  84 * You must take care when dereferencing iterator.this_arg
  85 * for multibyte types... the pointer is not aligned.  Use
  86 * get_unaligned((type *)iterator.this_arg) to dereference
  87 * iterator.this_arg for type "type" safely on all arches.
  88 *
  89 * Example code:
  90 * See Documentation/networking/radiotap-headers.txt
  91 */
  92
  93int ieee80211_radiotap_iterator_init(
  94        struct ieee80211_radiotap_iterator *iterator,
  95        struct ieee80211_radiotap_header *radiotap_header,
  96        int max_length, const struct ieee80211_radiotap_vendor_namespaces *vns)
  97{
  98        /* Linux only supports version 0 radiotap format */
  99        if (radiotap_header->it_version)
 100                return -EINVAL;
 101
 102        /* sanity check for allowed length and radiotap length field */
 103        if (max_length < get_unaligned_le16(&radiotap_header->it_len))
 104                return -EINVAL;
 105
 106        iterator->_rtheader = radiotap_header;
 107        iterator->_max_length = get_unaligned_le16(&radiotap_header->it_len);
 108        iterator->_arg_index = 0;
 109        iterator->_bitmap_shifter = get_unaligned_le32(&radiotap_header->it_present);
 110        iterator->_arg = (uint8_t *)radiotap_header + sizeof(*radiotap_header);
 111        iterator->_reset_on_ext = 0;
 112        iterator->_next_bitmap = &radiotap_header->it_present;
 113        iterator->_next_bitmap++;
 114        iterator->_vns = vns;
 115        iterator->current_namespace = &radiotap_ns;
 116        iterator->is_radiotap_ns = 1;
 117
 118        /* find payload start allowing for extended bitmap(s) */
 119
 120        if (iterator->_bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT)) {
 121                while (get_unaligned_le32(iterator->_arg) &
 122                                        (1 << IEEE80211_RADIOTAP_EXT)) {
 123                        iterator->_arg += sizeof(uint32_t);
 124
 125                        /*
 126                         * check for insanity where the present bitmaps
 127                         * keep claiming to extend up to or even beyond the
 128                         * stated radiotap header length
 129                         */
 130
 131                        if ((unsigned long)iterator->_arg -
 132                            (unsigned long)iterator->_rtheader >
 133                            (unsigned long)iterator->_max_length)
 134                                return -EINVAL;
 135                }
 136
 137                iterator->_arg += sizeof(uint32_t);
 138
 139                /*
 140                 * no need to check again for blowing past stated radiotap
 141                 * header length, because ieee80211_radiotap_iterator_next
 142                 * checks it before it is dereferenced
 143                 */
 144        }
 145
 146        iterator->this_arg = iterator->_arg;
 147
 148        /* we are all initialized happily */
 149
 150        return 0;
 151}
 152EXPORT_SYMBOL(ieee80211_radiotap_iterator_init);
 153
 154static void find_ns(struct ieee80211_radiotap_iterator *iterator,
 155                    uint32_t oui, uint8_t subns)
 156{
 157        int i;
 158
 159        iterator->current_namespace = NULL;
 160
 161        if (!iterator->_vns)
 162                return;
 163
 164        for (i = 0; i < iterator->_vns->n_ns; i++) {
 165                if (iterator->_vns->ns[i].oui != oui)
 166                        continue;
 167                if (iterator->_vns->ns[i].subns != subns)
 168                        continue;
 169
 170                iterator->current_namespace = &iterator->_vns->ns[i];
 171                break;
 172        }
 173}
 174
 175
 176
 177/**
 178 * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg
 179 * @iterator: radiotap_iterator to move to next arg (if any)
 180 *
 181 * Returns: 0 if there is an argument to handle,
 182 * -ENOENT if there are no more args or -EINVAL
 183 * if there is something else wrong.
 184 *
 185 * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*)
 186 * in @this_arg_index and sets @this_arg to point to the
 187 * payload for the field.  It takes care of alignment handling and extended
 188 * present fields.  @this_arg can be changed by the caller (eg,
 189 * incremented to move inside a compound argument like
 190 * IEEE80211_RADIOTAP_CHANNEL).  The args pointed to are in
 191 * little-endian format whatever the endianess of your CPU.
 192 *
 193 * Alignment Gotcha:
 194 * You must take care when dereferencing iterator.this_arg
 195 * for multibyte types... the pointer is not aligned.  Use
 196 * get_unaligned((type *)iterator.this_arg) to dereference
 197 * iterator.this_arg for type "type" safely on all arches.
 198 */
 199
 200int ieee80211_radiotap_iterator_next(
 201        struct ieee80211_radiotap_iterator *iterator)
 202{
 203        while (1) {
 204                int hit = 0;
 205                int pad, align, size, subns;
 206                uint32_t oui;
 207
 208                /* if no more EXT bits, that's it */
 209                if ((iterator->_arg_index % 32) == IEEE80211_RADIOTAP_EXT &&
 210                    !(iterator->_bitmap_shifter & 1))
 211                        return -ENOENT;
 212
 213                if (!(iterator->_bitmap_shifter & 1))
 214                        goto next_entry; /* arg not present */
 215
 216                /* get alignment/size of data */
 217                switch (iterator->_arg_index % 32) {
 218                case IEEE80211_RADIOTAP_RADIOTAP_NAMESPACE:
 219                case IEEE80211_RADIOTAP_EXT:
 220                        align = 1;
 221                        size = 0;
 222                        break;
 223                case IEEE80211_RADIOTAP_VENDOR_NAMESPACE:
 224                        align = 2;
 225                        size = 6;
 226                        break;
 227                default:
 228                        if (!iterator->current_namespace ||
 229                            iterator->_arg_index >= iterator->current_namespace->n_bits) {
 230                                if (iterator->current_namespace == &radiotap_ns)
 231                                        return -ENOENT;
 232                                align = 0;
 233                        } else {
 234                                align = iterator->current_namespace->align_size[iterator->_arg_index].align;
 235                                size = iterator->current_namespace->align_size[iterator->_arg_index].size;
 236                        }
 237                        if (!align) {
 238                                /* skip all subsequent data */
 239                                iterator->_arg = iterator->_next_ns_data;
 240                                /* give up on this namespace */
 241                                iterator->current_namespace = NULL;
 242                                goto next_entry;
 243                        }
 244                        break;
 245                }
 246
 247                /*
 248                 * arg is present, account for alignment padding
 249                 *
 250                 * Note that these alignments are relative to the start
 251                 * of the radiotap header.  There is no guarantee
 252                 * that the radiotap header itself is aligned on any
 253                 * kind of boundary.
 254                 *
 255                 * The above is why get_unaligned() is used to dereference
 256                 * multibyte elements from the radiotap area.
 257                 */
 258
 259                pad = ((unsigned long)iterator->_arg -
 260                       (unsigned long)iterator->_rtheader) & (align - 1);
 261
 262                if (pad)
 263                        iterator->_arg += align - pad;
 264
 265                if (iterator->_arg_index % 32 == IEEE80211_RADIOTAP_VENDOR_NAMESPACE) {
 266                        int vnslen;
 267
 268                        if ((unsigned long)iterator->_arg + size -
 269                            (unsigned long)iterator->_rtheader >
 270                            (unsigned long)iterator->_max_length)
 271                                return -EINVAL;
 272
 273                        oui = (*iterator->_arg << 16) |
 274                                (*(iterator->_arg + 1) << 8) |
 275                                *(iterator->_arg + 2);
 276                        subns = *(iterator->_arg + 3);
 277
 278                        find_ns(iterator, oui, subns);
 279
 280                        vnslen = get_unaligned_le16(iterator->_arg + 4);
 281                        iterator->_next_ns_data = iterator->_arg + size + vnslen;
 282                        if (!iterator->current_namespace)
 283                                size += vnslen;
 284                }
 285
 286                /*
 287                 * this is what we will return to user, but we need to
 288                 * move on first so next call has something fresh to test
 289                 */
 290                iterator->this_arg_index = iterator->_arg_index;
 291                iterator->this_arg = iterator->_arg;
 292                iterator->this_arg_size = size;
 293
 294                /* internally move on the size of this arg */
 295                iterator->_arg += size;
 296
 297                /*
 298                 * check for insanity where we are given a bitmap that
 299                 * claims to have more arg content than the length of the
 300                 * radiotap section.  We will normally end up equalling this
 301                 * max_length on the last arg, never exceeding it.
 302                 */
 303
 304                if ((unsigned long)iterator->_arg -
 305                    (unsigned long)iterator->_rtheader >
 306                    (unsigned long)iterator->_max_length)
 307                        return -EINVAL;
 308
 309                /* these special ones are valid in each bitmap word */
 310                switch (iterator->_arg_index % 32) {
 311                case IEEE80211_RADIOTAP_VENDOR_NAMESPACE:
 312                        iterator->_reset_on_ext = 1;
 313
 314                        iterator->is_radiotap_ns = 0;
 315                        /*
 316                         * If parser didn't register this vendor
 317                         * namespace with us, allow it to show it
 318                         * as 'raw. Do do that, set argument index
 319                         * to vendor namespace.
 320                         */
 321                        iterator->this_arg_index =
 322                                IEEE80211_RADIOTAP_VENDOR_NAMESPACE;
 323                        if (!iterator->current_namespace)
 324                                hit = 1;
 325                        goto next_entry;
 326                case IEEE80211_RADIOTAP_RADIOTAP_NAMESPACE:
 327                        iterator->_reset_on_ext = 1;
 328                        iterator->current_namespace = &radiotap_ns;
 329                        iterator->is_radiotap_ns = 1;
 330                        goto next_entry;
 331                case IEEE80211_RADIOTAP_EXT:
 332                        /*
 333                         * bit 31 was set, there is more
 334                         * -- move to next u32 bitmap
 335                         */
 336                        iterator->_bitmap_shifter =
 337                                get_unaligned_le32(iterator->_next_bitmap);
 338                        iterator->_next_bitmap++;
 339                        if (iterator->_reset_on_ext)
 340                                iterator->_arg_index = 0;
 341                        else
 342                                iterator->_arg_index++;
 343                        iterator->_reset_on_ext = 0;
 344                        break;
 345                default:
 346                        /* we've got a hit! */
 347                        hit = 1;
 348 next_entry:
 349                        iterator->_bitmap_shifter >>= 1;
 350                        iterator->_arg_index++;
 351                }
 352
 353                /* if we found a valid arg earlier, return it now */
 354                if (hit)
 355                        return 0;
 356        }
 357}
 358EXPORT_SYMBOL(ieee80211_radiotap_iterator_next);
 359
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