aboutsummaryrefslogtreecommitdiffstats
path: root/net/wireless/radiotap.c
blob: 68c11d0999175f2e7a2414f7346d1ad8c5929872 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
/*
 * Radiotap parser
 *
 * Copyright 2007		Andy Green <andy@warmcat.com>
 */

#include <net/cfg80211.h>
#include <net/ieee80211_radiotap.h>
#include <asm/unaligned.h>

/* function prototypes and related defs are in include/net/cfg80211.h */

/**
 * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization
 * @iterator: radiotap_iterator to initialize
 * @radiotap_header: radiotap header to parse
 * @max_length: total length we can parse into (eg, whole packet length)
 *
 * Returns: 0 or a negative error code if there is a problem.
 *
 * This function initializes an opaque iterator struct which can then
 * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap
 * argument which is present in the header.  It knows about extended
 * present headers and handles them.
 *
 * How to use:
 * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator
 * struct ieee80211_radiotap_iterator (no need to init the struct beforehand)
 * checking for a good 0 return code.  Then loop calling
 * __ieee80211_radiotap_iterator_next()... it returns either 0,
 * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem.
 * The iterator's @this_arg member points to the start of the argument
 * associated with the current argument index that is present, which can be
 * found in the iterator's @this_arg_index member.  This arg index corresponds
 * to the IEEE80211_RADIOTAP_... defines.
 *
 * Radiotap header length:
 * You can find the CPU-endian total radiotap header length in
 * iterator->max_length after executing ieee80211_radiotap_iterator_init()
 * successfully.
 *
 * Alignment Gotcha:
 * You must take care when dereferencing iterator.this_arg
 * for multibyte types... the pointer is not aligned.  Use
 * get_unaligned((type *)iterator.this_arg) to dereference
 * iterator.this_arg for type "type" safely on all arches.
 *
 * Example code:
 * See Documentation/networking/radiotap-headers.txt
 */

int ieee80211_radiotap_iterator_init(
    struct ieee80211_radiotap_iterator *iterator,
    struct ieee80211_radiotap_header *radiotap_header,
    int max_length)
{
	/* Linux only supports version 0 radiotap format */
	if (radiotap_header->it_version)
		return -EINVAL;

	/* sanity check for allowed length and radiotap length field */
	if (max_length < le16_to_cpu(get_unaligned(&radiotap_header->it_len)))
		return -EINVAL;

	iterator->rtheader = radiotap_header;
	iterator->max_length = le16_to_cpu(get_unaligned(
						&radiotap_header->it_len));
	iterator->arg_index = 0;
	iterator->bitmap_shifter = le32_to_cpu(get_unaligned(
						&radiotap_header->it_present));
	iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header);
	iterator->this_arg = NULL;

	/* find payload start allowing for extended bitmap(s) */

	if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) {
		while (le32_to_cpu(get_unaligned((__le32 *)iterator->arg)) &
				   (1<<IEEE80211_RADIOTAP_EXT)) {
			iterator->arg += sizeof(u32);

			/*
			 * check for insanity where the present bitmaps
			 * keep claiming to extend up to or even beyond the
			 * stated radiotap header length
			 */

			if (((ulong)iterator->arg -
			     (ulong)iterator->rtheader) > iterator->max_length)
				return -EINVAL;
		}

		iterator->arg += sizeof(u32);

		/*
		 * no need to check again for blowing past stated radiotap
		 * header length, because ieee80211_radiotap_iterator_next
		 * checks it before it is dereferenced
		 */
	}

	/* we are all initialized happily */

	return 0;
}
EXPORT_SYMBOL(ieee80211_radiotap_iterator_init);


/**
 * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg
 * @iterator: radiotap_iterator to move to next arg (if any)
 *
 * Returns: 0 if there is an argument to handle,
 * -ENOENT if there are no more args or -EINVAL
 * if there is something else wrong.
 *
 * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*)
 * in @this_arg_index and sets @this_arg to point to the
 * payload for the field.  It takes care of alignment handling and extended
 * present fields.  @this_arg can be changed by the caller (eg,
 * incremented to move inside a compound argument like
 * IEEE80211_RADIOTAP_CHANNEL).  The args pointed to are in
 * little-endian format whatever the endianess of your CPU.
 *
 * Alignment Gotcha:
 * You must take care when dereferencing iterator.this_arg
 * for multibyte types... the pointer is not aligned.  Use
 * get_unaligned((type *)iterator.this_arg) to dereference
 * iterator.this_arg for type "type" safely on all arches.
 */

int ieee80211_radiotap_iterator_next(
    struct ieee80211_radiotap_iterator *iterator)
{

	/*
	 * small length lookup table for all radiotap types we heard of
	 * starting from b0 in the bitmap, so we can walk the payload
	 * area of the radiotap header
	 *
	 * There is a requirement to pad args, so that args
	 * of a given length must begin at a boundary of that length
	 * -- but note that compound args are allowed (eg, 2 x u16
	 * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not
	 * a reliable indicator of alignment requirement.
	 *
	 * upper nybble: content alignment for arg
	 * lower nybble: content length for arg
	 */

	static const u8 rt_sizes[] = {
		[IEEE80211_RADIOTAP_TSFT] = 0x88,
		[IEEE80211_RADIOTAP_FLAGS] = 0x11,
		[IEEE80211_RADIOTAP_RATE] = 0x11,
		[IEEE80211_RADIOTAP_CHANNEL] = 0x24,
		[IEEE80211_RADIOTAP_FHSS] = 0x22,
		[IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11,
		[IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11,
		[IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22,
		[IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22,
		[IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22,
		[IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11,
		[IEEE80211_RADIOTAP_ANTENNA] = 0x11,
		[IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11,
		[IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11
		/*
		 * add more here as they are defined in
		 * include/net/ieee80211_radiotap.h
		 */
	};

	/*
	 * for every radiotap entry we can at
	 * least skip (by knowing the length)...
	 */

	while (iterator->arg_index < sizeof(rt_sizes)) {
		int hit = 0;
		int pad;

		if (!(iterator->bitmap_shifter & 1))
			goto next_entry; /* arg not present */

		/*
		 * arg is present, account for alignment padding
		 *  8-bit args can be at any alignment
		 * 16-bit args must start on 16-bit boundary
		 * 32-bit args must start on 32-bit boundary
		 * 64-bit args must start on 64-bit boundary
		 *
		 * note that total arg size can differ from alignment of
		 * elements inside arg, so we use upper nybble of length
		 * table to base alignment on
		 *
		 * also note: these alignments are ** relative to the
		 * start of the radiotap header **.  There is no guarantee
		 * that the radiotap header itself is aligned on any
		 * kind of boundary.
		 *
		 * the above is why get_unaligned() is used to dereference
		 * multibyte elements from the radiotap area
		 */

		pad = (((ulong)iterator->arg) -
			((ulong)iterator->rtheader)) &
			((rt_sizes[iterator->arg_index] >> 4) - 1);

		if (pad)
			iterator->arg +=
				(rt_sizes[iterator->arg_index] >> 4) - pad;

		/*
		 * this is what we will return to user, but we need to
		 * move on first so next call has something fresh to test
		 */
		iterator->this_arg_index = iterator->arg_index;
		iterator->this_arg = iterator->arg;
		hit = 1;

		/* internally move on the size of this arg */
		iterator->arg += rt_sizes[iterator->arg_index] & 0x0f;

		/*
		 * check for insanity where we are given a bitmap that
		 * claims to have more arg content than the length of the
		 * radiotap section.  We will normally end up equalling this
		 * max_length on the last arg, never exceeding it.
		 */

		if (((ulong)iterator->arg - (ulong)iterator->rtheader) >
		    iterator->max_length)
			return -EINVAL;

	next_entry:
		iterator->arg_index++;
		if (unlikely((iterator->arg_index & 31) == 0)) {
			/* completed current u32 bitmap */
			if (iterator->bitmap_shifter & 1) {
				/* b31 was set, there is more */
				/* move to next u32 bitmap */
				iterator->bitmap_shifter = le32_to_cpu(
					get_unaligned(iterator->next_bitmap));
				iterator->next_bitmap++;
			} else
				/* no more bitmaps: end */
				iterator->arg_index = sizeof(rt_sizes);
		} else /* just try the next bit */
			iterator->bitmap_shifter >>= 1;

		/* if we found a valid arg earlier, return it now */
		if (hit)
			return 0;
	}

	/* we don't know how to handle any more args, we're done */
	return -ENOENT;
}
EXPORT_SYMBOL(ieee80211_radiotap_iterator_next);