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      1 /*
      2  * Radiotap parser
      3  *
      4  * Copyright 2007		Andy Green <andy (at) warmcat.com>
      5  *
      6  * This program is free software; you can redistribute it and/or modify
      7  * it under the terms of the GNU General Public License version 2 as
      8  * published by the Free Software Foundation.
      9  *
     10  * Alternatively, this software may be distributed under the terms of BSD
     11  * license.
     12  *
     13  * See README and COPYING for more details.
     14  *
     15  *
     16  * Modified for userspace by Johannes Berg <johannes (at) sipsolutions.net>
     17  * I only modified some things on top to ease syncing should bugs be found.
     18  */
     19 
     20 #include "includes.h"
     21 
     22 #include "common.h"
     23 #include "radiotap_iter.h"
     24 
     25 #define le16_to_cpu		le_to_host16
     26 #define le32_to_cpu		le_to_host32
     27 #define __le32			uint32_t
     28 #define ulong			unsigned long
     29 #define unlikely(cond)		(cond)
     30 #define get_unaligned(p)					\
     31 ({								\
     32 	struct packed_dummy_struct {				\
     33 		typeof(*(p)) __val;				\
     34 	} __attribute__((packed)) *__ptr = (void *) (p);	\
     35 								\
     36 	__ptr->__val;						\
     37 })
     38 
     39 /* function prototypes and related defs are in radiotap_iter.h */
     40 
     41 /**
     42  * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization
     43  * @iterator: radiotap_iterator to initialize
     44  * @radiotap_header: radiotap header to parse
     45  * @max_length: total length we can parse into (eg, whole packet length)
     46  *
     47  * Returns: 0 or a negative error code if there is a problem.
     48  *
     49  * This function initializes an opaque iterator struct which can then
     50  * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap
     51  * argument which is present in the header.  It knows about extended
     52  * present headers and handles them.
     53  *
     54  * How to use:
     55  * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator
     56  * struct ieee80211_radiotap_iterator (no need to init the struct beforehand)
     57  * checking for a good 0 return code.  Then loop calling
     58  * __ieee80211_radiotap_iterator_next()... it returns either 0,
     59  * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem.
     60  * The iterator's @this_arg member points to the start of the argument
     61  * associated with the current argument index that is present, which can be
     62  * found in the iterator's @this_arg_index member.  This arg index corresponds
     63  * to the IEEE80211_RADIOTAP_... defines.
     64  *
     65  * Radiotap header length:
     66  * You can find the CPU-endian total radiotap header length in
     67  * iterator->max_length after executing ieee80211_radiotap_iterator_init()
     68  * successfully.
     69  *
     70  * Alignment Gotcha:
     71  * You must take care when dereferencing iterator.this_arg
     72  * for multibyte types... the pointer is not aligned.  Use
     73  * get_unaligned((type *)iterator.this_arg) to dereference
     74  * iterator.this_arg for type "type" safely on all arches.
     75  *
     76  * Example code:
     77  * See Documentation/networking/radiotap-headers.txt
     78  */
     79 
     80 int ieee80211_radiotap_iterator_init(
     81     struct ieee80211_radiotap_iterator *iterator,
     82     struct ieee80211_radiotap_header *radiotap_header,
     83     int max_length)
     84 {
     85 	/* Linux only supports version 0 radiotap format */
     86 	if (radiotap_header->it_version)
     87 		return -EINVAL;
     88 
     89 	/* sanity check for allowed length and radiotap length field */
     90 	if (max_length < le16_to_cpu(get_unaligned(&radiotap_header->it_len)))
     91 		return -EINVAL;
     92 
     93 	iterator->rtheader = radiotap_header;
     94 	iterator->max_length = le16_to_cpu(get_unaligned(
     95 						&radiotap_header->it_len));
     96 	iterator->arg_index = 0;
     97 	iterator->bitmap_shifter = le32_to_cpu(get_unaligned(
     98 						&radiotap_header->it_present));
     99 	iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header);
    100 	iterator->this_arg = NULL;
    101 
    102 	/* find payload start allowing for extended bitmap(s) */
    103 
    104 	if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) {
    105 		while (le32_to_cpu(get_unaligned((__le32 *)iterator->arg)) &
    106 				   (1<<IEEE80211_RADIOTAP_EXT)) {
    107 			iterator->arg += sizeof(u32);
    108 
    109 			/*
    110 			 * check for insanity where the present bitmaps
    111 			 * keep claiming to extend up to or even beyond the
    112 			 * stated radiotap header length
    113 			 */
    114 
    115 			if (((ulong)iterator->arg - (ulong)iterator->rtheader)
    116 			    > (ulong)iterator->max_length)
    117 				return -EINVAL;
    118 		}
    119 
    120 		iterator->arg += sizeof(u32);
    121 
    122 		/*
    123 		 * no need to check again for blowing past stated radiotap
    124 		 * header length, because ieee80211_radiotap_iterator_next
    125 		 * checks it before it is dereferenced
    126 		 */
    127 	}
    128 
    129 	/* we are all initialized happily */
    130 
    131 	return 0;
    132 }
    133 
    134 
    135 /**
    136  * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg
    137  * @iterator: radiotap_iterator to move to next arg (if any)
    138  *
    139  * Returns: 0 if there is an argument to handle,
    140  * -ENOENT if there are no more args or -EINVAL
    141  * if there is something else wrong.
    142  *
    143  * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*)
    144  * in @this_arg_index and sets @this_arg to point to the
    145  * payload for the field.  It takes care of alignment handling and extended
    146  * present fields.  @this_arg can be changed by the caller (eg,
    147  * incremented to move inside a compound argument like
    148  * IEEE80211_RADIOTAP_CHANNEL).  The args pointed to are in
    149  * little-endian format whatever the endianess of your CPU.
    150  *
    151  * Alignment Gotcha:
    152  * You must take care when dereferencing iterator.this_arg
    153  * for multibyte types... the pointer is not aligned.  Use
    154  * get_unaligned((type *)iterator.this_arg) to dereference
    155  * iterator.this_arg for type "type" safely on all arches.
    156  */
    157 
    158 int ieee80211_radiotap_iterator_next(
    159     struct ieee80211_radiotap_iterator *iterator)
    160 {
    161 
    162 	/*
    163 	 * small length lookup table for all radiotap types we heard of
    164 	 * starting from b0 in the bitmap, so we can walk the payload
    165 	 * area of the radiotap header
    166 	 *
    167 	 * There is a requirement to pad args, so that args
    168 	 * of a given length must begin at a boundary of that length
    169 	 * -- but note that compound args are allowed (eg, 2 x u16
    170 	 * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not
    171 	 * a reliable indicator of alignment requirement.
    172 	 *
    173 	 * upper nybble: content alignment for arg
    174 	 * lower nybble: content length for arg
    175 	 */
    176 
    177 	static const u8 rt_sizes[] = {
    178 		[IEEE80211_RADIOTAP_TSFT] = 0x88,
    179 		[IEEE80211_RADIOTAP_FLAGS] = 0x11,
    180 		[IEEE80211_RADIOTAP_RATE] = 0x11,
    181 		[IEEE80211_RADIOTAP_CHANNEL] = 0x24,
    182 		[IEEE80211_RADIOTAP_FHSS] = 0x22,
    183 		[IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11,
    184 		[IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11,
    185 		[IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22,
    186 		[IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22,
    187 		[IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22,
    188 		[IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11,
    189 		[IEEE80211_RADIOTAP_ANTENNA] = 0x11,
    190 		[IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11,
    191 		[IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11,
    192 		[IEEE80211_RADIOTAP_RX_FLAGS] = 0x22,
    193 		[IEEE80211_RADIOTAP_TX_FLAGS] = 0x22,
    194 		[IEEE80211_RADIOTAP_RTS_RETRIES] = 0x11,
    195 		[IEEE80211_RADIOTAP_DATA_RETRIES] = 0x11,
    196 		/*
    197 		 * add more here as they are defined in
    198 		 * include/net/ieee80211_radiotap.h
    199 		 */
    200 	};
    201 
    202 	/*
    203 	 * for every radiotap entry we can at
    204 	 * least skip (by knowing the length)...
    205 	 */
    206 
    207 	while (iterator->arg_index < (int) sizeof(rt_sizes)) {
    208 		int hit = 0;
    209 		int pad;
    210 
    211 		if (!(iterator->bitmap_shifter & 1))
    212 			goto next_entry; /* arg not present */
    213 
    214 		/*
    215 		 * arg is present, account for alignment padding
    216 		 *  8-bit args can be at any alignment
    217 		 * 16-bit args must start on 16-bit boundary
    218 		 * 32-bit args must start on 32-bit boundary
    219 		 * 64-bit args must start on 64-bit boundary
    220 		 *
    221 		 * note that total arg size can differ from alignment of
    222 		 * elements inside arg, so we use upper nybble of length
    223 		 * table to base alignment on
    224 		 *
    225 		 * also note: these alignments are ** relative to the
    226 		 * start of the radiotap header **.  There is no guarantee
    227 		 * that the radiotap header itself is aligned on any
    228 		 * kind of boundary.
    229 		 *
    230 		 * the above is why get_unaligned() is used to dereference
    231 		 * multibyte elements from the radiotap area
    232 		 */
    233 
    234 		pad = (((ulong)iterator->arg) -
    235 			((ulong)iterator->rtheader)) &
    236 			((rt_sizes[iterator->arg_index] >> 4) - 1);
    237 
    238 		if (pad)
    239 			iterator->arg +=
    240 				(rt_sizes[iterator->arg_index] >> 4) - pad;
    241 
    242 		/*
    243 		 * this is what we will return to user, but we need to
    244 		 * move on first so next call has something fresh to test
    245 		 */
    246 		iterator->this_arg_index = iterator->arg_index;
    247 		iterator->this_arg = iterator->arg;
    248 		hit = 1;
    249 
    250 		/* internally move on the size of this arg */
    251 		iterator->arg += rt_sizes[iterator->arg_index] & 0x0f;
    252 
    253 		/*
    254 		 * check for insanity where we are given a bitmap that
    255 		 * claims to have more arg content than the length of the
    256 		 * radiotap section.  We will normally end up equalling this
    257 		 * max_length on the last arg, never exceeding it.
    258 		 */
    259 
    260 		if (((ulong)iterator->arg - (ulong)iterator->rtheader) >
    261 		    (ulong) iterator->max_length)
    262 			return -EINVAL;
    263 
    264 	next_entry:
    265 		iterator->arg_index++;
    266 		if (unlikely((iterator->arg_index & 31) == 0)) {
    267 			/* completed current u32 bitmap */
    268 			if (iterator->bitmap_shifter & 1) {
    269 				/* b31 was set, there is more */
    270 				/* move to next u32 bitmap */
    271 				iterator->bitmap_shifter = le32_to_cpu(
    272 					get_unaligned(iterator->next_bitmap));
    273 				iterator->next_bitmap++;
    274 			} else
    275 				/* no more bitmaps: end */
    276 				iterator->arg_index = sizeof(rt_sizes);
    277 		} else /* just try the next bit */
    278 			iterator->bitmap_shifter >>= 1;
    279 
    280 		/* if we found a valid arg earlier, return it now */
    281 		if (hit)
    282 			return 0;
    283 	}
    284 
    285 	/* we don't know how to handle any more args, we're done */
    286 	return -ENOENT;
    287 }
    288