radiotap.c revision 8d520ff1dc2da35cdca849e982051b86468016d8
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 80int 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 158int 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} 288