Andy Green | 179f831 | 2007-07-10 19:29:38 +0200 | [diff] [blame] | 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, |
Johannes Berg | dde4e47 | 2007-08-13 14:04:30 +0200 | [diff] [blame^] | 164 | [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11, |
| 165 | [IEEE80211_RADIOTAP_RX_FLAGS] = 0x22, |
| 166 | [IEEE80211_RADIOTAP_TX_FLAGS] = 0x22, |
| 167 | [IEEE80211_RADIOTAP_RTS_RETRIES] = 0x11, |
| 168 | [IEEE80211_RADIOTAP_DATA_RETRIES] = 0x11, |
Andy Green | 179f831 | 2007-07-10 19:29:38 +0200 | [diff] [blame] | 169 | /* |
| 170 | * add more here as they are defined in |
| 171 | * include/net/ieee80211_radiotap.h |
| 172 | */ |
| 173 | }; |
| 174 | |
| 175 | /* |
| 176 | * for every radiotap entry we can at |
| 177 | * least skip (by knowing the length)... |
| 178 | */ |
| 179 | |
| 180 | while (iterator->arg_index < sizeof(rt_sizes)) { |
| 181 | int hit = 0; |
| 182 | int pad; |
| 183 | |
| 184 | if (!(iterator->bitmap_shifter & 1)) |
| 185 | goto next_entry; /* arg not present */ |
| 186 | |
| 187 | /* |
| 188 | * arg is present, account for alignment padding |
| 189 | * 8-bit args can be at any alignment |
| 190 | * 16-bit args must start on 16-bit boundary |
| 191 | * 32-bit args must start on 32-bit boundary |
| 192 | * 64-bit args must start on 64-bit boundary |
| 193 | * |
| 194 | * note that total arg size can differ from alignment of |
| 195 | * elements inside arg, so we use upper nybble of length |
| 196 | * table to base alignment on |
| 197 | * |
| 198 | * also note: these alignments are ** relative to the |
| 199 | * start of the radiotap header **. There is no guarantee |
| 200 | * that the radiotap header itself is aligned on any |
| 201 | * kind of boundary. |
| 202 | * |
| 203 | * the above is why get_unaligned() is used to dereference |
| 204 | * multibyte elements from the radiotap area |
| 205 | */ |
| 206 | |
| 207 | pad = (((ulong)iterator->arg) - |
| 208 | ((ulong)iterator->rtheader)) & |
| 209 | ((rt_sizes[iterator->arg_index] >> 4) - 1); |
| 210 | |
| 211 | if (pad) |
| 212 | iterator->arg += |
| 213 | (rt_sizes[iterator->arg_index] >> 4) - pad; |
| 214 | |
| 215 | /* |
| 216 | * this is what we will return to user, but we need to |
| 217 | * move on first so next call has something fresh to test |
| 218 | */ |
| 219 | iterator->this_arg_index = iterator->arg_index; |
| 220 | iterator->this_arg = iterator->arg; |
| 221 | hit = 1; |
| 222 | |
| 223 | /* internally move on the size of this arg */ |
| 224 | iterator->arg += rt_sizes[iterator->arg_index] & 0x0f; |
| 225 | |
| 226 | /* |
| 227 | * check for insanity where we are given a bitmap that |
| 228 | * claims to have more arg content than the length of the |
| 229 | * radiotap section. We will normally end up equalling this |
| 230 | * max_length on the last arg, never exceeding it. |
| 231 | */ |
| 232 | |
| 233 | if (((ulong)iterator->arg - (ulong)iterator->rtheader) > |
| 234 | iterator->max_length) |
| 235 | return -EINVAL; |
| 236 | |
| 237 | next_entry: |
| 238 | iterator->arg_index++; |
| 239 | if (unlikely((iterator->arg_index & 31) == 0)) { |
| 240 | /* completed current u32 bitmap */ |
| 241 | if (iterator->bitmap_shifter & 1) { |
| 242 | /* b31 was set, there is more */ |
| 243 | /* move to next u32 bitmap */ |
| 244 | iterator->bitmap_shifter = le32_to_cpu( |
| 245 | get_unaligned(iterator->next_bitmap)); |
| 246 | iterator->next_bitmap++; |
| 247 | } else |
| 248 | /* no more bitmaps: end */ |
| 249 | iterator->arg_index = sizeof(rt_sizes); |
| 250 | } else /* just try the next bit */ |
| 251 | iterator->bitmap_shifter >>= 1; |
| 252 | |
| 253 | /* if we found a valid arg earlier, return it now */ |
| 254 | if (hit) |
| 255 | return 0; |
| 256 | } |
| 257 | |
| 258 | /* we don't know how to handle any more args, we're done */ |
| 259 | return -ENOENT; |
| 260 | } |
| 261 | EXPORT_SYMBOL(ieee80211_radiotap_iterator_next); |