Commit 179f831b authored by Andy Green's avatar Andy Green Committed by John W. Linville

[PATCH] cfg80211: Radiotap parser

Generic code to walk through the fields in a radiotap header, accounting
for nasties like extended "field present" bitfields and alignment rules
Signed-off-by: default avatarAndy Green <andy@warmcat.com>
Signed-off-by: default avatarJiri Benc <jbenc@suse.cz>
Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
parent 08d1f215
......@@ -84,4 +84,69 @@ Example valid radiotap header
0x01 //<-- antenna
Using the Radiotap Parser
-------------------------
If you are having to parse a radiotap struct, you can radically simplify the
job by using the radiotap parser that lives in net/wireless/radiotap.c and has
its prototypes available in include/net/cfg80211.h. You use it like this:
#include <net/cfg80211.h>
/* buf points to the start of the radiotap header part */
int MyFunction(u8 * buf, int buflen)
{
int pkt_rate_100kHz = 0, antenna = 0, pwr = 0;
struct ieee80211_radiotap_iterator iterator;
int ret = ieee80211_radiotap_iterator_init(&iterator, buf, buflen);
while (!ret) {
ret = ieee80211_radiotap_iterator_next(&iterator);
if (ret)
continue;
/* see if this argument is something we can use */
switch (iterator.this_arg_index) {
/*
* 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.
*/
case IEEE80211_RADIOTAP_RATE:
/* radiotap "rate" u8 is in
* 500kbps units, eg, 0x02=1Mbps
*/
pkt_rate_100kHz = (*iterator.this_arg) * 5;
break;
case IEEE80211_RADIOTAP_ANTENNA:
/* radiotap uses 0 for 1st ant */
antenna = *iterator.this_arg);
break;
case IEEE80211_RADIOTAP_DBM_TX_POWER:
pwr = *iterator.this_arg;
break;
default:
break;
}
} /* while more rt headers */
if (ret != -ENOENT)
return TXRX_DROP;
/* discard the radiotap header part */
buf += iterator.max_length;
buflen -= iterator.max_length;
...
}
Andy Green <andy@warmcat.com>
......@@ -11,6 +11,44 @@
* Copyright 2006 Johannes Berg <johannes@sipsolutions.net>
*/
/* Radiotap header iteration
* implemented in net/wireless/radiotap.c
* docs in Documentation/networking/radiotap-headers.txt
*/
/**
* struct ieee80211_radiotap_iterator - tracks walk thru present radiotap args
* @rtheader: pointer to the radiotap header we are walking through
* @max_length: length of radiotap header in cpu byte ordering
* @this_arg_index: IEEE80211_RADIOTAP_... index of current arg
* @this_arg: pointer to current radiotap arg
* @arg_index: internal next argument index
* @arg: internal next argument pointer
* @next_bitmap: internal pointer to next present u32
* @bitmap_shifter: internal shifter for curr u32 bitmap, b0 set == arg present
*/
struct ieee80211_radiotap_iterator {
struct ieee80211_radiotap_header *rtheader;
int max_length;
int this_arg_index;
u8 *this_arg;
int arg_index;
u8 *arg;
__le32 *next_bitmap;
u32 bitmap_shifter;
};
extern int ieee80211_radiotap_iterator_init(
struct ieee80211_radiotap_iterator *iterator,
struct ieee80211_radiotap_header *radiotap_header,
int max_length);
extern int ieee80211_radiotap_iterator_next(
struct ieee80211_radiotap_iterator *iterator);
/* from net/wireless.h */
struct wiphy;
......
obj-$(CONFIG_WIRELESS_EXT) += wext.o
obj-$(CONFIG_CFG80211) += cfg80211.o
cfg80211-y += core.o sysfs.o
cfg80211-y += core.o sysfs.o radiotap.o
/*
* 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);
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