net/wireless/radiotap.c

/*
 * Radiotap parser
 *
 * Copyright 2007		Andy Green <andy@warmcat.com>
 * Copyright 2009		Johannes Berg <johannes@sipsolutions.net>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See COPYING for more details.
 */

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

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

static const struct radiotap_align_size rtap_namespace_sizes[] = {
	[IEEE80211_RADIOTAP_TSFT] = { .align = 8, .size = 8, },
	[IEEE80211_RADIOTAP_FLAGS] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_RATE] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_CHANNEL] = { .align = 2, .size = 4, },
	[IEEE80211_RADIOTAP_FHSS] = { .align = 2, .size = 2, },
	[IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_DBM_ANTNOISE] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_LOCK_QUALITY] = { .align = 2, .size = 2, },
	[IEEE80211_RADIOTAP_TX_ATTENUATION] = { .align = 2, .size = 2, },
	[IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = { .align = 2, .size = 2, },
	[IEEE80211_RADIOTAP_DBM_TX_POWER] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_ANTENNA] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_DB_ANTSIGNAL] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_DB_ANTNOISE] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_RX_FLAGS] = { .align = 2, .size = 2, },
	[IEEE80211_RADIOTAP_TX_FLAGS] = { .align = 2, .size = 2, },
	[IEEE80211_RADIOTAP_RTS_RETRIES] = { .align = 1, .size = 1, },
	[IEEE80211_RADIOTAP_DATA_RETRIES] = { .align = 1, .size = 1, },
	/*
	 * add more here as they are defined in radiotap.h
	 */
};

static const struct ieee80211_radiotap_namespace radiotap_ns = {
	.n_bits = ARRAY_SIZE(rtap_namespace_sizes),
	.align_size = rtap_namespace_sizes,
};

/**
 * 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, const struct ieee80211_radiotap_vendor_namespaces *vns)
{
	/* 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 < get_unaligned_le16(&radiotap_header->it_len))
		return -EINVAL;

	iterator->_rtheader = radiotap_header;
	iterator->_max_length = get_unaligned_le16(&radiotap_header->it_len);
	iterator->_arg_index = 0;
	iterator->_bitmap_shifter = get_unaligned_le32(&radiotap_header->it_present);
	iterator->_arg = (uint8_t *)radiotap_header + sizeof(*radiotap_header);
	iterator->_reset_on_ext = 0;
	iterator->_next_bitmap = &radiotap_header->it_present;
	iterator->_next_bitmap++;
	iterator->_vns = vns;
	iterator->current_namespace = &radiotap_ns;
	iterator->is_radiotap_ns = 1;

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

	if (iterator->_bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT)) {
		while (get_unaligned_le32(iterator->_arg) &
					(1 << IEEE80211_RADIOTAP_EXT)) {
			iterator->_arg += sizeof(uint32_t);

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

			if ((unsigned long)iterator->_arg -
			    (unsigned long)iterator->_rtheader >
			    (unsigned long)iterator->_max_length)
				return -EINVAL;
		}

		iterator->_arg += sizeof(uint32_t);

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

	iterator->this_arg = iterator->_arg;

	/* we are all initialized happily */

	return 0;
}
EXPORT_SYMBOL(ieee80211_radiotap_iterator_init);

static void find_ns(struct ieee80211_radiotap_iterator *iterator,
		    uint32_t oui, uint8_t subns)
{
	int i;

	iterator->current_namespace = NULL;

	if (!iterator->_vns)
		return;

	for (i = 0; i < iterator->_vns->n_ns; i++) {
		if (iterator->_vns->ns[i].oui != oui)
			continue;
		if (iterator->_vns->ns[i].subns != subns)
			continue;

		iterator->current_namespace = &iterator->_vns->ns[i];
		break;
	}
}



/**
 * 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)
{
	while (1) {
		int hit = 0;
		int pad, align, size, subns, vnslen;
		uint32_t oui;

		/* if no more EXT bits, that's it */
		if ((iterator->_arg_index % 32) == IEEE80211_RADIOTAP_EXT &&
		    !(iterator->_bitmap_shifter & 1))
			return -ENOENT;

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

		/* get alignment/size of data */
		switch (iterator->_arg_index % 32) {
		case IEEE80211_RADIOTAP_RADIOTAP_NAMESPACE:
		case IEEE80211_RADIOTAP_EXT:
			align = 1;
			size = 0;
			break;
		case IEEE80211_RADIOTAP_VENDOR_NAMESPACE:
			align = 2;
			size = 6;
			break;
		default:
			if (!iterator->current_namespace ||
			    iterator->_arg_index >= iterator->current_namespace->n_bits) {
				if (iterator->current_namespace == &radiotap_ns)
					return -ENOENT;
				align = 0;
			} else {
				align = iterator->current_namespace->align_size[iterator->_arg_index].align;
				size = iterator->current_namespace->align_size[iterator->_arg_index].size;
			}
			if (!align) {
				/* skip all subsequent data */
				iterator->_arg = iterator->_next_ns_data;
				/* give up on this namespace */
				iterator->current_namespace = NULL;
				goto next_entry;
			}
			break;
		}

		/*
		 * arg is present, account for alignment padding
		 *
		 * Note that 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 = ((unsigned long)iterator->_arg -
		       (unsigned long)iterator->_rtheader) & (align - 1);

		if (pad)
			iterator->_arg += align - 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;
		iterator->this_arg_size = size;

		/* internally move on the size of this arg */
		iterator->_arg += size;

		/*
		 * 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 ((unsigned long)iterator->_arg -
		    (unsigned long)iterator->_rtheader >
		    (unsigned long)iterator->_max_length)
			return -EINVAL;

		/* these special ones are valid in each bitmap word */
		switch (iterator->_arg_index % 32) {
		case IEEE80211_RADIOTAP_VENDOR_NAMESPACE:
			iterator->_bitmap_shifter >>= 1;
			iterator->_arg_index++;

			iterator->_reset_on_ext = 1;

			vnslen = get_unaligned_le16(iterator->this_arg + 4);
			iterator->_next_ns_data = iterator->_arg + vnslen;
			oui = (*iterator->this_arg << 16) |
				(*(iterator->this_arg + 1) << 8) |
				*(iterator->this_arg + 2);
			subns = *(iterator->this_arg + 3);

			find_ns(iterator, oui, subns);

			iterator->is_radiotap_ns = 0;
			/* allow parsers to show this information */
			iterator->this_arg_index =
				IEEE80211_RADIOTAP_VENDOR_NAMESPACE;
			iterator->this_arg_size += vnslen;
			if ((unsigned long)iterator->this_arg +
			    iterator->this_arg_size -
			    (unsigned long)iterator->_rtheader >
			    (unsigned long)(unsigned long)iterator->_max_length)
				return -EINVAL;
			hit = 1;
			break;
		case IEEE80211_RADIOTAP_RADIOTAP_NAMESPACE:
			iterator->_bitmap_shifter >>= 1;
			iterator->_arg_index++;

			iterator->_reset_on_ext = 1;
			iterator->current_namespace = &radiotap_ns;
			iterator->is_radiotap_ns = 1;
			break;
		case IEEE80211_RADIOTAP_EXT:
			/*
			 * bit 31 was set, there is more
			 * -- move to next u32 bitmap
			 */
			iterator->_bitmap_shifter =
				get_unaligned_le32(iterator->_next_bitmap);
			iterator->_next_bitmap++;
			if (iterator->_reset_on_ext)
				iterator->_arg_index = 0;
			else
				iterator->_arg_index++;
			iterator->_reset_on_ext = 0;
			break;
		default:
			/* we've got a hit! */
			hit = 1;
 next_entry:
			iterator->_bitmap_shifter >>= 1;
			iterator->_arg_index++;
		}

		/* if we found a valid arg earlier, return it now */
		if (hit)
			return 0;
	}
}
EXPORT_SYMBOL(ieee80211_radiotap_iterator_next);