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 < le16_to_cpu(get_unaligned(&radiotap_header->it_len))) 63 return -EINVAL; 64 65 iterator->rtheader = radiotap_header; 66 iterator->max_length = le16_to_cpu(get_unaligned( 67 &radiotap_header->it_len)); 68 iterator->arg_index = 0; 69 iterator->bitmap_shifter = le32_to_cpu(get_unaligned( 70 &radiotap_header->it_present)); 71 iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header); 72 iterator->this_arg = NULL; 73 74 /* find payload start allowing for extended bitmap(s) */ 75 76 if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) { 77 while (le32_to_cpu(get_unaligned((__le32 *)iterator->arg)) & 78 (1<<IEEE80211_RADIOTAP_EXT)) { 79 iterator->arg += sizeof(u32); 80 81 /* 82 * check for insanity where the present bitmaps 83 * keep claiming to extend up to or even beyond the 84 * stated radiotap header length 85 */ 86 87 if (((ulong)iterator->arg - 88 (ulong)iterator->rtheader) > iterator->max_length) 89 return -EINVAL; 90 } 91 92 iterator->arg += sizeof(u32); 93 94 /* 95 * no need to check again for blowing past stated radiotap 96 * header length, because ieee80211_radiotap_iterator_next 97 * checks it before it is dereferenced 98 */ 99 } 100 101 /* we are all initialized happily */ 102 103 return 0; 104 } 105 EXPORT_SYMBOL(ieee80211_radiotap_iterator_init); 106 107 108 /** 109 * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg 110 * @iterator: radiotap_iterator to move to next arg (if any) 111 * 112 * Returns: 0 if there is an argument to handle, 113 * -ENOENT if there are no more args or -EINVAL 114 * if there is something else wrong. 115 * 116 * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*) 117 * in @this_arg_index and sets @this_arg to point to the 118 * payload for the field. It takes care of alignment handling and extended 119 * present fields. @this_arg can be changed by the caller (eg, 120 * incremented to move inside a compound argument like 121 * IEEE80211_RADIOTAP_CHANNEL). The args pointed to are in 122 * little-endian format whatever the endianess of your CPU. 123 * 124 * Alignment Gotcha: 125 * You must take care when dereferencing iterator.this_arg 126 * for multibyte types... the pointer is not aligned. Use 127 * get_unaligned((type *)iterator.this_arg) to dereference 128 * iterator.this_arg for type "type" safely on all arches. 129 */ 130 131 int ieee80211_radiotap_iterator_next( 132 struct ieee80211_radiotap_iterator *iterator) 133 { 134 135 /* 136 * small length lookup table for all radiotap types we heard of 137 * starting from b0 in the bitmap, so we can walk the payload 138 * area of the radiotap header 139 * 140 * There is a requirement to pad args, so that args 141 * of a given length must begin at a boundary of that length 142 * -- but note that compound args are allowed (eg, 2 x u16 143 * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not 144 * a reliable indicator of alignment requirement. 145 * 146 * upper nybble: content alignment for arg 147 * lower nybble: content length for arg 148 */ 149 150 static const u8 rt_sizes[] = { 151 [IEEE80211_RADIOTAP_TSFT] = 0x88, 152 [IEEE80211_RADIOTAP_FLAGS] = 0x11, 153 [IEEE80211_RADIOTAP_RATE] = 0x11, 154 [IEEE80211_RADIOTAP_CHANNEL] = 0x24, 155 [IEEE80211_RADIOTAP_FHSS] = 0x22, 156 [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11, 157 [IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11, 158 [IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22, 159 [IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22, 160 [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22, 161 [IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11, 162 [IEEE80211_RADIOTAP_ANTENNA] = 0x11, 163 [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11, 164 [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11 165 /* 166 * add more here as they are defined in 167 * include/net/ieee80211_radiotap.h 168 */ 169 }; 170 171 /* 172 * for every radiotap entry we can at 173 * least skip (by knowing the length)... 174 */ 175 176 while (iterator->arg_index < sizeof(rt_sizes)) { 177 int hit = 0; 178 int pad; 179 180 if (!(iterator->bitmap_shifter & 1)) 181 goto next_entry; /* arg not present */ 182 183 /* 184 * arg is present, account for alignment padding 185 * 8-bit args can be at any alignment 186 * 16-bit args must start on 16-bit boundary 187 * 32-bit args must start on 32-bit boundary 188 * 64-bit args must start on 64-bit boundary 189 * 190 * note that total arg size can differ from alignment of 191 * elements inside arg, so we use upper nybble of length 192 * table to base alignment on 193 * 194 * also note: these alignments are ** relative to the 195 * start of the radiotap header **. There is no guarantee 196 * that the radiotap header itself is aligned on any 197 * kind of boundary. 198 * 199 * the above is why get_unaligned() is used to dereference 200 * multibyte elements from the radiotap area 201 */ 202 203 pad = (((ulong)iterator->arg) - 204 ((ulong)iterator->rtheader)) & 205 ((rt_sizes[iterator->arg_index] >> 4) - 1); 206 207 if (pad) 208 iterator->arg += 209 (rt_sizes[iterator->arg_index] >> 4) - pad; 210 211 /* 212 * this is what we will return to user, but we need to 213 * move on first so next call has something fresh to test 214 */ 215 iterator->this_arg_index = iterator->arg_index; 216 iterator->this_arg = iterator->arg; 217 hit = 1; 218 219 /* internally move on the size of this arg */ 220 iterator->arg += rt_sizes[iterator->arg_index] & 0x0f; 221 222 /* 223 * check for insanity where we are given a bitmap that 224 * claims to have more arg content than the length of the 225 * radiotap section. We will normally end up equalling this 226 * max_length on the last arg, never exceeding it. 227 */ 228 229 if (((ulong)iterator->arg - (ulong)iterator->rtheader) > 230 iterator->max_length) 231 return -EINVAL; 232 233 next_entry: 234 iterator->arg_index++; 235 if (unlikely((iterator->arg_index & 31) == 0)) { 236 /* completed current u32 bitmap */ 237 if (iterator->bitmap_shifter & 1) { 238 /* b31 was set, there is more */ 239 /* move to next u32 bitmap */ 240 iterator->bitmap_shifter = le32_to_cpu( 241 get_unaligned(iterator->next_bitmap)); 242 iterator->next_bitmap++; 243 } else 244 /* no more bitmaps: end */ 245 iterator->arg_index = sizeof(rt_sizes); 246 } else /* just try the next bit */ 247 iterator->bitmap_shifter >>= 1; 248 249 /* if we found a valid arg earlier, return it now */ 250 if (hit) 251 return 0; 252 } 253 254 /* we don't know how to handle any more args, we're done */ 255 return -ENOENT; 256 } 257 EXPORT_SYMBOL(ieee80211_radiotap_iterator_next); 258