src/utils/radiotap.c

   1 /*
   2  * Radiotap parser
   3  *
   4  * Copyright 2007               Andy Green <andy@warmcat.com>
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  * Alternatively, this software may be distributed under the terms of BSD
  11  * license.
  12  *
  13  * See README and COPYING for more details.
  14  *
  15  *
  16  * Modified for userspace by Johannes Berg <johannes@sipsolutions.net>
  17  * I only modified some things on top to ease syncing should bugs be found.
  18  */
  19
  20 #include "includes.h"
  21
  22 #include "common.h"
  23 #include "radiotap_iter.h"
  24
  25 #define le16_to_cpu             le_to_host16
  26 #define le32_to_cpu             le_to_host32
  27 #define __le32                  uint32_t
  28 #define ulong                   unsigned long
  29 #define unlikely(cond)          (cond)
  30 #define get_unaligned(p)                                        \
  31 ({                                                              \
  32         struct packed_dummy_struct {                            \
  33                 typeof(*(p)) __val;                             \
  34         } __attribute__((packed)) *__ptr = (void *) (p);        \
  35                                                                 \
  36         __ptr->__val;                                           \
  37 })
  38
  39 /* function prototypes and related defs are in radiotap_iter.h */
  40
  41 /**
  42  * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization
  43  * @iterator: radiotap_iterator to initialize
  44  * @radiotap_header: radiotap header to parse
  45  * @max_length: total length we can parse into (eg, whole packet length)
  46  *
  47  * Returns: 0 or a negative error code if there is a problem.
  48  *
  49  * This function initializes an opaque iterator struct which can then
  50  * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap
  51  * argument which is present in the header.  It knows about extended
  52  * present headers and handles them.
  53  *
  54  * How to use:
  55  * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator
  56  * struct ieee80211_radiotap_iterator (no need to init the struct beforehand)
  57  * checking for a good 0 return code.  Then loop calling
  58  * __ieee80211_radiotap_iterator_next()... it returns either 0,
  59  * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem.
  60  * The iterator's @this_arg member points to the start of the argument
  61  * associated with the current argument index that is present, which can be
  62  * found in the iterator's @this_arg_index member.  This arg index corresponds
  63  * to the IEEE80211_RADIOTAP_... defines.
  64  *
  65  * Radiotap header length:
  66  * You can find the CPU-endian total radiotap header length in
  67  * iterator->max_length after executing ieee80211_radiotap_iterator_init()
  68  * successfully.
  69  *
  70  * Alignment Gotcha:
  71  * You must take care when dereferencing iterator.this_arg
  72  * for multibyte types... the pointer is not aligned.  Use
  73  * get_unaligned((type *)iterator.this_arg) to dereference
  74  * iterator.this_arg for type "type" safely on all arches.
  75  *
  76  * Example code:
  77  * See Documentation/networking/radiotap-headers.txt
  78  */
  79
  80 int ieee80211_radiotap_iterator_init(
  81     struct ieee80211_radiotap_iterator *iterator,
  82     struct ieee80211_radiotap_header *radiotap_header,
  83     int max_length)
  84 {
  85         /* Linux only supports version 0 radiotap format */
  86         if (radiotap_header->it_version)
  87                 return -EINVAL;
  88
  89         /* sanity check for allowed length and radiotap length field */
  90         if (max_length < le16_to_cpu(get_unaligned(&radiotap_header->it_len)))
  91                 return -EINVAL;
  92
  93         iterator->rtheader = radiotap_header;
  94         iterator->max_length = le16_to_cpu(get_unaligned(
  95                                                 &radiotap_header->it_len));
  96         iterator->arg_index = 0;
  97         iterator->bitmap_shifter = le32_to_cpu(get_unaligned(
  98                                                 &radiotap_header->it_present));
  99         iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header);
 100         iterator->this_arg = NULL;
 101
 102         /* find payload start allowing for extended bitmap(s) */
 103
 104         if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) {
 105                 while (le32_to_cpu(get_unaligned((__le32 *)iterator->arg)) &
 106                                    (1<<IEEE80211_RADIOTAP_EXT)) {
 107                         iterator->arg += sizeof(u32);
 108
 109                         /*
 110                          * check for insanity where the present bitmaps
 111                          * keep claiming to extend up to or even beyond the
 112                          * stated radiotap header length
 113                          */
 114
 115                         if (((ulong)iterator->arg - (ulong)iterator->rtheader)
 116                             > (ulong)iterator->max_length)
 117                                 return -EINVAL;
 118                 }
 119
 120                 iterator->arg += sizeof(u32);
 121
 122                 /*
 123                  * no need to check again for blowing past stated radiotap
 124                  * header length, because ieee80211_radiotap_iterator_next
 125                  * checks it before it is dereferenced
 126                  */
 127         }
 128
 129         /* we are all initialized happily */
 130
 131         return 0;
 132 }
 133
 134
 135 /**
 136  * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg
 137  * @iterator: radiotap_iterator to move to next arg (if any)
 138  *
 139  * Returns: 0 if there is an argument to handle,
 140  * -ENOENT if there are no more args or -EINVAL
 141  * if there is something else wrong.
 142  *
 143  * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*)
 144  * in @this_arg_index and sets @this_arg to point to the
 145  * payload for the field.  It takes care of alignment handling and extended
 146  * present fields.  @this_arg can be changed by the caller (eg,
 147  * incremented to move inside a compound argument like
 148  * IEEE80211_RADIOTAP_CHANNEL).  The args pointed to are in
 149  * little-endian format whatever the endianess of your CPU.
 150  *
 151  * Alignment Gotcha:
 152  * You must take care when dereferencing iterator.this_arg
 153  * for multibyte types... the pointer is not aligned.  Use
 154  * get_unaligned((type *)iterator.this_arg) to dereference
 155  * iterator.this_arg for type "type" safely on all arches.
 156  */
 157
 158 int ieee80211_radiotap_iterator_next(
 159     struct ieee80211_radiotap_iterator *iterator)
 160 {
 161
 162         /*
 163          * small length lookup table for all radiotap types we heard of
 164          * starting from b0 in the bitmap, so we can walk the payload
 165          * area of the radiotap header
 166          *
 167          * There is a requirement to pad args, so that args
 168          * of a given length must begin at a boundary of that length
 169          * -- but note that compound args are allowed (eg, 2 x u16
 170          * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not
 171          * a reliable indicator of alignment requirement.
 172          *
 173          * upper nybble: content alignment for arg
 174          * lower nybble: content length for arg
 175          */
 176
 177         static const u8 rt_sizes[] = {
 178                 [IEEE80211_RADIOTAP_TSFT] = 0x88,
 179                 [IEEE80211_RADIOTAP_FLAGS] = 0x11,
 180                 [IEEE80211_RADIOTAP_RATE] = 0x11,
 181                 [IEEE80211_RADIOTAP_CHANNEL] = 0x24,
 182                 [IEEE80211_RADIOTAP_FHSS] = 0x22,
 183                 [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11,
 184                 [IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11,
 185                 [IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22,
 186                 [IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22,
 187                 [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22,
 188                 [IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11,
 189                 [IEEE80211_RADIOTAP_ANTENNA] = 0x11,
 190                 [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11,
 191                 [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11,
 192                 [IEEE80211_RADIOTAP_RX_FLAGS] = 0x22,
 193                 [IEEE80211_RADIOTAP_TX_FLAGS] = 0x22,
 194                 [IEEE80211_RADIOTAP_RTS_RETRIES] = 0x11,
 195                 [IEEE80211_RADIOTAP_DATA_RETRIES] = 0x11,
 196                 /*
 197                  * add more here as they are defined in
 198                  * include/net/ieee80211_radiotap.h
 199                  */
 200         };
 201
 202         /*
 203          * for every radiotap entry we can at
 204          * least skip (by knowing the length)...
 205          */
 206
 207         while (iterator->arg_index < (int) sizeof(rt_sizes)) {
 208                 int hit = 0;
 209                 int pad;
 210
 211                 if (!(iterator->bitmap_shifter & 1))
 212                         goto next_entry; /* arg not present */
 213
 214                 /*
 215                  * arg is present, account for alignment padding
 216                  *  8-bit args can be at any alignment
 217                  * 16-bit args must start on 16-bit boundary
 218                  * 32-bit args must start on 32-bit boundary
 219                  * 64-bit args must start on 64-bit boundary
 220                  *
 221                  * note that total arg size can differ from alignment of
 222                  * elements inside arg, so we use upper nybble of length
 223                  * table to base alignment on
 224                  *
 225                  * also note: these alignments are ** relative to the
 226                  * start of the radiotap header **.  There is no guarantee
 227                  * that the radiotap header itself is aligned on any
 228                  * kind of boundary.
 229                  *
 230                  * the above is why get_unaligned() is used to dereference
 231                  * multibyte elements from the radiotap area
 232                  */
 233
 234                 pad = (((ulong)iterator->arg) -
 235                         ((ulong)iterator->rtheader)) &
 236                         ((rt_sizes[iterator->arg_index] >> 4) - 1);
 237
 238                 if (pad)
 239                         iterator->arg +=
 240                                 (rt_sizes[iterator->arg_index] >> 4) - pad;
 241
 242                 /*
 243                  * this is what we will return to user, but we need to
 244                  * move on first so next call has something fresh to test
 245                  */
 246                 iterator->this_arg_index = iterator->arg_index;
 247                 iterator->this_arg = iterator->arg;
 248                 hit = 1;
 249
 250                 /* internally move on the size of this arg */
 251                 iterator->arg += rt_sizes[iterator->arg_index] & 0x0f;
 252
 253                 /*
 254                  * check for insanity where we are given a bitmap that
 255                  * claims to have more arg content than the length of the
 256                  * radiotap section.  We will normally end up equalling this
 257                  * max_length on the last arg, never exceeding it.
 258                  */
 259
 260                 if (((ulong)iterator->arg - (ulong)iterator->rtheader) >
 261                     (ulong) iterator->max_length)
 262                         return -EINVAL;
 263
 264         next_entry:
 265                 iterator->arg_index++;
 266                 if (unlikely((iterator->arg_index & 31) == 0)) {
 267                         /* completed current u32 bitmap */
 268                         if (iterator->bitmap_shifter & 1) {
 269                                 /* b31 was set, there is more */
 270                                 /* move to next u32 bitmap */
 271                                 iterator->bitmap_shifter = le32_to_cpu(
 272                                         get_unaligned(iterator->next_bitmap));
 273                                 iterator->next_bitmap++;
 274                         } else
 275                                 /* no more bitmaps: end */
 276                                 iterator->arg_index = sizeof(rt_sizes);
 277                 } else /* just try the next bit */
 278                         iterator->bitmap_shifter >>= 1;
 279
 280                 /* if we found a valid arg earlier, return it now */
 281                 if (hit)
 282                         return 0;
 283         }
 284
 285         /* we don't know how to handle any more args, we're done */
 286         return -ENOENT;
 287 }