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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 |
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