1 /* 2 * Radiotap parser 3 * 4 * Copyright 2007 Andy Green <[email protected]> 5 */ 6 7 #include "inject_80211.h" 8 #include "radiotap.h" 9 10 /** 11 * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization 12 * @iterator: radiotap_iterator to initialize 13 * @radiotap_header: radiotap header to parse 14 * @max_length: total length we can parse into (eg, whole packet length) 15 * 16 * Returns: 0 or a negative error code if there is a problem. 17 * 18 * This function initializes an opaque iterator struct which can then 19 * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap 20 * argument which is present in the header. It knows about extended 21 * present headers and handles them. 22 * 23 * How to use: 24 * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator 25 * struct ieee80211_radiotap_iterator (no need to init the struct beforehand) 26 * checking for a good 0 return code. Then loop calling 27 * __ieee80211_radiotap_iterator_next()... it returns either 0, 28 * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem. 29 * The iterator's @this_arg member points to the start of the argument 30 * associated with the current argument index that is present, which can be 31 * found in the iterator's @this_arg_index member. This arg index corresponds 32 * to the IEEE80211_RADIOTAP_... defines. 33 * 34 * Radiotap header length: 35 * You can find the CPU-endian total radiotap header length in 36 * iterator->max_length after executing ieee80211_radiotap_iterator_init() 37 * successfully. 38 * 39 * Example code: 40 * See Documentation/networking/radiotap-headers.txt 41 */ 42 43 int ieee80211_radiotap_iterator_init( 44 struct ieee80211_radiotap_iterator *iterator, 45 struct ieee80211_radiotap_header *radiotap_header, 46 int max_length) 47 { 48 /* Linux only supports version 0 radiotap format */ 49 if (radiotap_header->it_version) 50 return -EINVAL; 51 52 /* sanity check for allowed length and radiotap length field */ 53 if (max_length < le16_to_cpu(radiotap_header->it_len)) 54 return -EINVAL; 55 56 iterator->rtheader = radiotap_header; 57 iterator->max_length = le16_to_cpu(radiotap_header->it_len); 58 iterator->arg_index = 0; 59 iterator->bitmap_shifter = le32_to_cpu(radiotap_header->it_present); 60 iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header); 61 iterator->this_arg = 0; 62 63 /* find payload start allowing for extended bitmap(s) */ 64 65 if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) { 66 while (le32_to_cpu(*((u32 *)iterator->arg)) & 67 (1<<IEEE80211_RADIOTAP_EXT)) { 68 iterator->arg += sizeof(u32); 69 70 /* 71 * check for insanity where the present bitmaps 72 * keep claiming to extend up to or even beyond the 73 * stated radiotap header length 74 */ 75 76 if (((ulong)iterator->arg - 77 (ulong)iterator->rtheader) > iterator->max_length) 78 return -EINVAL; 79 } 80 81 iterator->arg += sizeof(u32); 82 83 /* 84 * no need to check again for blowing past stated radiotap 85 * header length, because ieee80211_radiotap_iterator_next 86 * checks it before it is dereferenced 87 */ 88 } 89 90 /* we are all initialized happily */ 91 92 return 0; 93 } 94 95 96 /** 97 * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg 98 * @iterator: radiotap_iterator to move to next arg (if any) 99 * 100 * Returns: 0 if there is an argument to handle, 101 * -ENOENT if there are no more args or -EINVAL 102 * if there is something else wrong. 103 * 104 * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*) 105 * in @this_arg_index and sets @this_arg to point to the 106 * payload for the field. It takes care of alignment handling and extended 107 * present fields. @this_arg can be changed by the caller (eg, 108 * incremented to move inside a compound argument like 109 * IEEE80211_RADIOTAP_CHANNEL). The args pointed to are in 110 * little-endian format whatever the endianness of your CPU. 111 */ 112 113 int ieee80211_radiotap_iterator_next( 114 struct ieee80211_radiotap_iterator *iterator) 115 { 116 117 /* 118 * small length lookup table for all radiotap types we heard of 119 * starting from b0 in the bitmap, so we can walk the payload 120 * area of the radiotap header 121 * 122 * There is a requirement to pad args, so that args 123 * of a given length must begin at a boundary of that length 124 * -- but note that compound args are allowed (eg, 2 x u16 125 * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not 126 * a reliable indicator of alignment requirement. 127 * 128 * upper nybble: content alignment for arg 129 * lower nybble: content length for arg 130 */ 131 132 static const u8 rt_sizes[] = { 133 [IEEE80211_RADIOTAP_TSFT] = 0x88, 134 [IEEE80211_RADIOTAP_FLAGS] = 0x11, 135 [IEEE80211_RADIOTAP_RATE] = 0x11, 136 [IEEE80211_RADIOTAP_CHANNEL] = 0x24, 137 [IEEE80211_RADIOTAP_FHSS] = 0x22, 138 [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11, 139 [IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11, 140 [IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22, 141 [IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22, 142 [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22, 143 [IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11, 144 [IEEE80211_RADIOTAP_ANTENNA] = 0x11, 145 [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11, 146 [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11, 147 [IEEE80211_RADIOTAP_RX_FLAGS] = 0x22, 148 [IEEE80211_RADIOTAP_TX_FLAGS] = 0x22, 149 [IEEE80211_RADIOTAP_RTS_RETRIES] = 0x11, 150 [IEEE80211_RADIOTAP_DATA_RETRIES] = 0x11, 151 [IEEE80211_RADIOTAP_MCS] = 0x13, 152 [IEEE80211_RADIOTAP_AMPDU_STATUS] = 0x48 153 /* 154 * add more here as they are defined in 155 * include/net/ieee80211_radiotap.h 156 */ 157 }; 158 159 /* 160 * for every radiotap entry we can at 161 * least skip (by knowing the length)... 162 */ 163 164 while (iterator->arg_index < sizeof(rt_sizes)) { 165 int hit = 0; 166 int pad; 167 168 if (!(iterator->bitmap_shifter & 1)) 169 goto next_entry; /* arg not present */ 170 171 /* 172 * arg is present, account for alignment padding 173 * 8-bit args can be at any alignment 174 * 16-bit args must start on 16-bit boundary 175 * 32-bit args must start on 32-bit boundary 176 * 64-bit args must start on 64-bit boundary 177 * 178 * note that total arg size can differ from alignment of 179 * elements inside arg, so we use upper nybble of length 180 * table to base alignment on 181 * 182 * also note: these alignments are ** relative to the 183 * start of the radiotap header **. There is no guarantee 184 * that the radiotap header itself is aligned on any 185 * kind of boundary. 186 */ 187 188 pad = (((ulong)iterator->arg) - 189 ((ulong)iterator->rtheader)) & 190 ((rt_sizes[iterator->arg_index] >> 4) - 1); 191 192 if (pad) 193 iterator->arg += 194 (rt_sizes[iterator->arg_index] >> 4) - pad; 195 196 /* 197 * this is what we will return to user, but we need to 198 * move on first so next call has something fresh to test 199 */ 200 iterator->this_arg_index = iterator->arg_index; 201 iterator->this_arg = iterator->arg; 202 hit = 1; 203 204 /* internally move on the size of this arg */ 205 iterator->arg += rt_sizes[iterator->arg_index] & 0x0f; 206 207 /* 208 * check for insanity where we are given a bitmap that 209 * claims to have more arg content than the length of the 210 * radiotap section. We will normally end up equalling this 211 * max_length on the last arg, never exceeding it. 212 */ 213 214 if (((ulong)iterator->arg - (ulong)iterator->rtheader) > 215 iterator->max_length) 216 return -EINVAL; 217 218 next_entry: 219 iterator->arg_index++; 220 if (unlikely((iterator->arg_index & 31) == 0)) { 221 /* completed current u32 bitmap */ 222 if (iterator->bitmap_shifter & 1) { 223 /* b31 was set, there is more */ 224 /* move to next u32 bitmap */ 225 iterator->bitmap_shifter = 226 le32_to_cpu(*iterator->next_bitmap); 227 iterator->next_bitmap++; 228 } else { 229 /* no more bitmaps: end */ 230 iterator->arg_index = sizeof(rt_sizes); 231 } 232 } else { /* just try the next bit */ 233 iterator->bitmap_shifter >>= 1; 234 } 235 236 /* if we found a valid arg earlier, return it now */ 237 if (hit) 238 return 0; 239 } 240 241 /* we don't know how to handle any more args, we're done */ 242 return -ENOENT; 243 } 244 245