1 /* 2 * Radiotap parser 3 * 4 * Copyright 2007 Andy Green <andy@warmcat.com> 5 */ 6 7 #include <net/cfg80211.h> 8 #include <net/ieee80211_radiotap.h> 9 #include <asm/unaligned.h> 10 11 /* function prototypes and related defs are in include/net/cfg80211.h */ 12 13 /** 14 * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization 15 * @iterator: radiotap_iterator to initialize 16 * @radiotap_header: radiotap header to parse 17 * @max_length: total length we can parse into (eg, whole packet length) 18 * 19 * Returns: 0 or a negative error code if there is a problem. 20 * 21 * This function initializes an opaque iterator struct which can then 22 * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap 23 * argument which is present in the header. It knows about extended 24 * present headers and handles them. 25 * 26 * How to use: 27 * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator 28 * struct ieee80211_radiotap_iterator (no need to init the struct beforehand) 29 * checking for a good 0 return code. Then loop calling 30 * __ieee80211_radiotap_iterator_next()... it returns either 0, 31 * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem. 32 * The iterator's @this_arg member points to the start of the argument 33 * associated with the current argument index that is present, which can be 34 * found in the iterator's @this_arg_index member. This arg index corresponds 35 * to the IEEE80211_RADIOTAP_... defines. 36 * 37 * Radiotap header length: 38 * You can find the CPU-endian total radiotap header length in 39 * iterator->max_length after executing ieee80211_radiotap_iterator_init() 40 * successfully. 41 * 42 * Alignment Gotcha: 43 * You must take care when dereferencing iterator.this_arg 44 * for multibyte types... the pointer is not aligned. Use 45 * get_unaligned((type *)iterator.this_arg) to dereference 46 * iterator.this_arg for type "type" safely on all arches. 47 * 48 * Example code: 49 * See Documentation/networking/radiotap-headers.txt 50 */ 51 52 int ieee80211_radiotap_iterator_init( 53 struct ieee80211_radiotap_iterator *iterator, 54 struct ieee80211_radiotap_header *radiotap_header, 55 int max_length) 56 { 57 /* Linux only supports version 0 radiotap format */ 58 if (radiotap_header->it_version) 59 return -EINVAL; 60 61 /* sanity check for allowed length and radiotap length field */ 62 if (max_length < get_unaligned_le16(&radiotap_header->it_len)) 63 return -EINVAL; 64 65 iterator->rtheader = radiotap_header; 66 iterator->max_length = get_unaligned_le16(&radiotap_header->it_len); 67 iterator->arg_index = 0; 68 iterator->bitmap_shifter = get_unaligned_le32(&radiotap_header->it_present); 69 iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header); 70 iterator->this_arg = NULL; 71 72 /* find payload start allowing for extended bitmap(s) */ 73 74 if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) { 75 while (get_unaligned_le32(iterator->arg) & 76 (1 << IEEE80211_RADIOTAP_EXT)) { 77 iterator->arg += sizeof(u32); 78 79 /* 80 * check for insanity where the present bitmaps 81 * keep claiming to extend up to or even beyond the 82 * stated radiotap header length 83 */ 84 85 if (((ulong)iterator->arg - 86 (ulong)iterator->rtheader) > iterator->max_length) 87 return -EINVAL; 88 } 89 90 iterator->arg += sizeof(u32); 91 92 /* 93 * no need to check again for blowing past stated radiotap 94 * header length, because ieee80211_radiotap_iterator_next 95 * checks it before it is dereferenced 96 */ 97 } 98 99 /* we are all initialized happily */ 100 101 return 0; 102 } 103 EXPORT_SYMBOL(ieee80211_radiotap_iterator_init); 104 105 106 /** 107 * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg 108 * @iterator: radiotap_iterator to move to next arg (if any) 109 * 110 * Returns: 0 if there is an argument to handle, 111 * -ENOENT if there are no more args or -EINVAL 112 * if there is something else wrong. 113 * 114 * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*) 115 * in @this_arg_index and sets @this_arg to point to the 116 * payload for the field. It takes care of alignment handling and extended 117 * present fields. @this_arg can be changed by the caller (eg, 118 * incremented to move inside a compound argument like 119 * IEEE80211_RADIOTAP_CHANNEL). The args pointed to are in 120 * little-endian format whatever the endianess of your CPU. 121 * 122 * Alignment Gotcha: 123 * You must take care when dereferencing iterator.this_arg 124 * for multibyte types... the pointer is not aligned. Use 125 * get_unaligned((type *)iterator.this_arg) to dereference 126 * iterator.this_arg for type "type" safely on all arches. 127 */ 128 129 int ieee80211_radiotap_iterator_next( 130 struct ieee80211_radiotap_iterator *iterator) 131 { 132 133 /* 134 * small length lookup table for all radiotap types we heard of 135 * starting from b0 in the bitmap, so we can walk the payload 136 * area of the radiotap header 137 * 138 * There is a requirement to pad args, so that args 139 * of a given length must begin at a boundary of that length 140 * -- but note that compound args are allowed (eg, 2 x u16 141 * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not 142 * a reliable indicator of alignment requirement. 143 * 144 * upper nybble: content alignment for arg 145 * lower nybble: content length for arg 146 */ 147 148 static const u8 rt_sizes[] = { 149 [IEEE80211_RADIOTAP_TSFT] = 0x88, 150 [IEEE80211_RADIOTAP_FLAGS] = 0x11, 151 [IEEE80211_RADIOTAP_RATE] = 0x11, 152 [IEEE80211_RADIOTAP_CHANNEL] = 0x24, 153 [IEEE80211_RADIOTAP_FHSS] = 0x22, 154 [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11, 155 [IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11, 156 [IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22, 157 [IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22, 158 [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22, 159 [IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11, 160 [IEEE80211_RADIOTAP_ANTENNA] = 0x11, 161 [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11, 162 [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11, 163 [IEEE80211_RADIOTAP_RX_FLAGS] = 0x22, 164 [IEEE80211_RADIOTAP_TX_FLAGS] = 0x22, 165 [IEEE80211_RADIOTAP_RTS_RETRIES] = 0x11, 166 [IEEE80211_RADIOTAP_DATA_RETRIES] = 0x11, 167 /* 168 * add more here as they are defined in 169 * include/net/ieee80211_radiotap.h 170 */ 171 }; 172 173 /* 174 * for every radiotap entry we can at 175 * least skip (by knowing the length)... 176 */ 177 178 while (iterator->arg_index < sizeof(rt_sizes)) { 179 int hit = 0; 180 int pad; 181 182 if (!(iterator->bitmap_shifter & 1)) 183 goto next_entry; /* arg not present */ 184 185 /* 186 * arg is present, account for alignment padding 187 * 8-bit args can be at any alignment 188 * 16-bit args must start on 16-bit boundary 189 * 32-bit args must start on 32-bit boundary 190 * 64-bit args must start on 64-bit boundary 191 * 192 * note that total arg size can differ from alignment of 193 * elements inside arg, so we use upper nybble of length 194 * table to base alignment on 195 * 196 * also note: these alignments are ** relative to the 197 * start of the radiotap header **. There is no guarantee 198 * that the radiotap header itself is aligned on any 199 * kind of boundary. 200 * 201 * the above is why get_unaligned() is used to dereference 202 * multibyte elements from the radiotap area 203 */ 204 205 pad = (((ulong)iterator->arg) - 206 ((ulong)iterator->rtheader)) & 207 ((rt_sizes[iterator->arg_index] >> 4) - 1); 208 209 if (pad) 210 iterator->arg += 211 (rt_sizes[iterator->arg_index] >> 4) - pad; 212 213 /* 214 * this is what we will return to user, but we need to 215 * move on first so next call has something fresh to test 216 */ 217 iterator->this_arg_index = iterator->arg_index; 218 iterator->this_arg = iterator->arg; 219 hit = 1; 220 221 /* internally move on the size of this arg */ 222 iterator->arg += rt_sizes[iterator->arg_index] & 0x0f; 223 224 /* 225 * check for insanity where we are given a bitmap that 226 * claims to have more arg content than the length of the 227 * radiotap section. We will normally end up equalling this 228 * max_length on the last arg, never exceeding it. 229 */ 230 231 if (((ulong)iterator->arg - (ulong)iterator->rtheader) > 232 iterator->max_length) 233 return -EINVAL; 234 235 next_entry: 236 iterator->arg_index++; 237 if (unlikely((iterator->arg_index & 31) == 0)) { 238 /* completed current u32 bitmap */ 239 if (iterator->bitmap_shifter & 1) { 240 /* b31 was set, there is more */ 241 /* move to next u32 bitmap */ 242 iterator->bitmap_shifter = 243 get_unaligned_le32(iterator->next_bitmap); 244 iterator->next_bitmap++; 245 } else 246 /* no more bitmaps: end */ 247 iterator->arg_index = sizeof(rt_sizes); 248 } else /* just try the next bit */ 249 iterator->bitmap_shifter >>= 1; 250 251 /* if we found a valid arg earlier, return it now */ 252 if (hit) 253 return 0; 254 } 255 256 /* we don't know how to handle any more args, we're done */ 257 return -ENOENT; 258 } 259 EXPORT_SYMBOL(ieee80211_radiotap_iterator_next); 260