[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: Andy Green <andy@warmcat.com> Signed-off-by: Jiri Benc <jbenc@suse.cz> Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Andy Green
John W. Linville
parent
08d1f2155c
commit
179f831bc3
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@ -84,4 +84,69 @@ Example valid radiotap header
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0x01 //<-- antenna
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Using the Radiotap Parser
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-------------------------
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If you are having to parse a radiotap struct, you can radically simplify the
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job by using the radiotap parser that lives in net/wireless/radiotap.c and has
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its prototypes available in include/net/cfg80211.h. You use it like this:
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#include <net/cfg80211.h>
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/* buf points to the start of the radiotap header part */
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int MyFunction(u8 * buf, int buflen)
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{
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int pkt_rate_100kHz = 0, antenna = 0, pwr = 0;
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struct ieee80211_radiotap_iterator iterator;
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int ret = ieee80211_radiotap_iterator_init(&iterator, buf, buflen);
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while (!ret) {
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ret = ieee80211_radiotap_iterator_next(&iterator);
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if (ret)
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continue;
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/* see if this argument is something we can use */
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switch (iterator.this_arg_index) {
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/*
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* You must take care when dereferencing iterator.this_arg
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* for multibyte types... the pointer is not aligned. Use
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* get_unaligned((type *)iterator.this_arg) to dereference
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* iterator.this_arg for type "type" safely on all arches.
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*/
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case IEEE80211_RADIOTAP_RATE:
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/* radiotap "rate" u8 is in
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* 500kbps units, eg, 0x02=1Mbps
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*/
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pkt_rate_100kHz = (*iterator.this_arg) * 5;
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break;
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case IEEE80211_RADIOTAP_ANTENNA:
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/* radiotap uses 0 for 1st ant */
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antenna = *iterator.this_arg);
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break;
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case IEEE80211_RADIOTAP_DBM_TX_POWER:
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pwr = *iterator.this_arg;
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break;
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default:
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break;
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}
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} /* while more rt headers */
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if (ret != -ENOENT)
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return TXRX_DROP;
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/* discard the radiotap header part */
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buf += iterator.max_length;
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buflen -= iterator.max_length;
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...
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}
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Andy Green <andy@warmcat.com>
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@ -11,6 +11,44 @@
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* Copyright 2006 Johannes Berg <johannes@sipsolutions.net>
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*/
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/* Radiotap header iteration
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* implemented in net/wireless/radiotap.c
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* docs in Documentation/networking/radiotap-headers.txt
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*/
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/**
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* struct ieee80211_radiotap_iterator - tracks walk thru present radiotap args
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* @rtheader: pointer to the radiotap header we are walking through
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* @max_length: length of radiotap header in cpu byte ordering
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* @this_arg_index: IEEE80211_RADIOTAP_... index of current arg
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* @this_arg: pointer to current radiotap arg
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* @arg_index: internal next argument index
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* @arg: internal next argument pointer
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* @next_bitmap: internal pointer to next present u32
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* @bitmap_shifter: internal shifter for curr u32 bitmap, b0 set == arg present
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*/
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struct ieee80211_radiotap_iterator {
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struct ieee80211_radiotap_header *rtheader;
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int max_length;
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int this_arg_index;
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u8 *this_arg;
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int arg_index;
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u8 *arg;
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__le32 *next_bitmap;
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u32 bitmap_shifter;
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};
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extern int ieee80211_radiotap_iterator_init(
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struct ieee80211_radiotap_iterator *iterator,
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struct ieee80211_radiotap_header *radiotap_header,
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int max_length);
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extern int ieee80211_radiotap_iterator_next(
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struct ieee80211_radiotap_iterator *iterator);
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/* from net/wireless.h */
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struct wiphy;
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@ -1,4 +1,4 @@
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obj-$(CONFIG_WIRELESS_EXT) += wext.o
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obj-$(CONFIG_CFG80211) += cfg80211.o
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cfg80211-y += core.o sysfs.o
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cfg80211-y += core.o sysfs.o radiotap.o
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@ -0,0 +1,257 @@
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/*
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* Radiotap parser
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*
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* Copyright 2007 Andy Green <andy@warmcat.com>
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*/
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#include <net/cfg80211.h>
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#include <net/ieee80211_radiotap.h>
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#include <asm/unaligned.h>
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/* function prototypes and related defs are in include/net/cfg80211.h */
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/**
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* ieee80211_radiotap_iterator_init - radiotap parser iterator initialization
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* @iterator: radiotap_iterator to initialize
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* @radiotap_header: radiotap header to parse
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* @max_length: total length we can parse into (eg, whole packet length)
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*
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* Returns: 0 or a negative error code if there is a problem.
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*
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* This function initializes an opaque iterator struct which can then
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* be passed to ieee80211_radiotap_iterator_next() to visit every radiotap
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* argument which is present in the header. It knows about extended
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* present headers and handles them.
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*
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* How to use:
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* call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator
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* struct ieee80211_radiotap_iterator (no need to init the struct beforehand)
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* checking for a good 0 return code. Then loop calling
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* __ieee80211_radiotap_iterator_next()... it returns either 0,
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* -ENOENT if there are no more args to parse, or -EINVAL if there is a problem.
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* The iterator's @this_arg member points to the start of the argument
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* associated with the current argument index that is present, which can be
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* found in the iterator's @this_arg_index member. This arg index corresponds
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* to the IEEE80211_RADIOTAP_... defines.
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*
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* Radiotap header length:
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* You can find the CPU-endian total radiotap header length in
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* iterator->max_length after executing ieee80211_radiotap_iterator_init()
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* successfully.
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*
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* Alignment Gotcha:
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* You must take care when dereferencing iterator.this_arg
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* for multibyte types... the pointer is not aligned. Use
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* get_unaligned((type *)iterator.this_arg) to dereference
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* iterator.this_arg for type "type" safely on all arches.
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*
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* Example code:
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* See Documentation/networking/radiotap-headers.txt
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*/
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int ieee80211_radiotap_iterator_init(
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struct ieee80211_radiotap_iterator *iterator,
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struct ieee80211_radiotap_header *radiotap_header,
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int max_length)
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{
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/* Linux only supports version 0 radiotap format */
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if (radiotap_header->it_version)
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return -EINVAL;
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/* sanity check for allowed length and radiotap length field */
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if (max_length < le16_to_cpu(get_unaligned(&radiotap_header->it_len)))
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return -EINVAL;
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iterator->rtheader = radiotap_header;
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iterator->max_length = le16_to_cpu(get_unaligned(
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&radiotap_header->it_len));
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iterator->arg_index = 0;
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iterator->bitmap_shifter = le32_to_cpu(get_unaligned(
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&radiotap_header->it_present));
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iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header);
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iterator->this_arg = NULL;
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/* find payload start allowing for extended bitmap(s) */
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if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) {
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while (le32_to_cpu(get_unaligned((__le32 *)iterator->arg)) &
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(1<<IEEE80211_RADIOTAP_EXT)) {
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iterator->arg += sizeof(u32);
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/*
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* check for insanity where the present bitmaps
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* keep claiming to extend up to or even beyond the
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* stated radiotap header length
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*/
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if (((ulong)iterator->arg -
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(ulong)iterator->rtheader) > iterator->max_length)
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return -EINVAL;
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}
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iterator->arg += sizeof(u32);
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/*
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* no need to check again for blowing past stated radiotap
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* header length, because ieee80211_radiotap_iterator_next
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* checks it before it is dereferenced
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*/
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}
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/* we are all initialized happily */
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return 0;
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}
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EXPORT_SYMBOL(ieee80211_radiotap_iterator_init);
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/**
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* ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg
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* @iterator: radiotap_iterator to move to next arg (if any)
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*
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* Returns: 0 if there is an argument to handle,
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* -ENOENT if there are no more args or -EINVAL
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* if there is something else wrong.
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*
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* This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*)
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* in @this_arg_index and sets @this_arg to point to the
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* payload for the field. It takes care of alignment handling and extended
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* present fields. @this_arg can be changed by the caller (eg,
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* incremented to move inside a compound argument like
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* IEEE80211_RADIOTAP_CHANNEL). The args pointed to are in
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* little-endian format whatever the endianess of your CPU.
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*
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* Alignment Gotcha:
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* You must take care when dereferencing iterator.this_arg
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* for multibyte types... the pointer is not aligned. Use
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* get_unaligned((type *)iterator.this_arg) to dereference
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* iterator.this_arg for type "type" safely on all arches.
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*/
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int ieee80211_radiotap_iterator_next(
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struct ieee80211_radiotap_iterator *iterator)
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{
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/*
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* small length lookup table for all radiotap types we heard of
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* starting from b0 in the bitmap, so we can walk the payload
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* area of the radiotap header
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*
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* There is a requirement to pad args, so that args
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* of a given length must begin at a boundary of that length
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* -- but note that compound args are allowed (eg, 2 x u16
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* for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not
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* a reliable indicator of alignment requirement.
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*
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* upper nybble: content alignment for arg
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* lower nybble: content length for arg
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*/
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static const u8 rt_sizes[] = {
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[IEEE80211_RADIOTAP_TSFT] = 0x88,
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[IEEE80211_RADIOTAP_FLAGS] = 0x11,
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[IEEE80211_RADIOTAP_RATE] = 0x11,
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[IEEE80211_RADIOTAP_CHANNEL] = 0x24,
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[IEEE80211_RADIOTAP_FHSS] = 0x22,
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[IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11,
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[IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11,
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[IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22,
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[IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22,
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[IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22,
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[IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11,
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[IEEE80211_RADIOTAP_ANTENNA] = 0x11,
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[IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11,
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[IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11
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/*
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* add more here as they are defined in
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* include/net/ieee80211_radiotap.h
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*/
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};
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/*
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* for every radiotap entry we can at
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* least skip (by knowing the length)...
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*/
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while (iterator->arg_index < sizeof(rt_sizes)) {
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int hit = 0;
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int pad;
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if (!(iterator->bitmap_shifter & 1))
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goto next_entry; /* arg not present */
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/*
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* arg is present, account for alignment padding
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* 8-bit args can be at any alignment
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* 16-bit args must start on 16-bit boundary
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* 32-bit args must start on 32-bit boundary
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* 64-bit args must start on 64-bit boundary
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*
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* note that total arg size can differ from alignment of
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* elements inside arg, so we use upper nybble of length
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* table to base alignment on
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*
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* also note: these alignments are ** relative to the
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* start of the radiotap header **. There is no guarantee
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* that the radiotap header itself is aligned on any
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* kind of boundary.
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*
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* the above is why get_unaligned() is used to dereference
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* multibyte elements from the radiotap area
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*/
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pad = (((ulong)iterator->arg) -
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((ulong)iterator->rtheader)) &
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((rt_sizes[iterator->arg_index] >> 4) - 1);
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if (pad)
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iterator->arg +=
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(rt_sizes[iterator->arg_index] >> 4) - pad;
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/*
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* this is what we will return to user, but we need to
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* move on first so next call has something fresh to test
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*/
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iterator->this_arg_index = iterator->arg_index;
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iterator->this_arg = iterator->arg;
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hit = 1;
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/* internally move on the size of this arg */
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iterator->arg += rt_sizes[iterator->arg_index] & 0x0f;
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/*
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* check for insanity where we are given a bitmap that
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* claims to have more arg content than the length of the
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* radiotap section. We will normally end up equalling this
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* max_length on the last arg, never exceeding it.
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*/
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if (((ulong)iterator->arg - (ulong)iterator->rtheader) >
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iterator->max_length)
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return -EINVAL;
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next_entry:
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iterator->arg_index++;
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if (unlikely((iterator->arg_index & 31) == 0)) {
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/* completed current u32 bitmap */
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if (iterator->bitmap_shifter & 1) {
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/* b31 was set, there is more */
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/* move to next u32 bitmap */
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iterator->bitmap_shifter = le32_to_cpu(
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get_unaligned(iterator->next_bitmap));
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iterator->next_bitmap++;
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} else
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/* no more bitmaps: end */
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iterator->arg_index = sizeof(rt_sizes);
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} else /* just try the next bit */
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iterator->bitmap_shifter >>= 1;
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/* if we found a valid arg earlier, return it now */
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if (hit)
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return 0;
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}
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/* we don't know how to handle any more args, we're done */
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return -ENOENT;
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}
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EXPORT_SYMBOL(ieee80211_radiotap_iterator_next);
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