From: Andy Green <andy@xxxxxxxxxxx>
Try #1
- Based on Johannes Berg's comments, broke out the radiotap parsing into
its own file as part of cfg80211
- From same comments, added mask constant for b31 of arg presence bitfield
to ieee80211_radiotap.h
- Fixed subtle but nasty bug with alignment: args in the radiotap area are
aligned *relative to the start of the header* now. The header is not
guaranteed to align to anything (it is randomly in an skb data area).
===================================================
diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 47e4544..098d4b6 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -74,6 +74,41 @@ struct key_params {
u32 cipher;
};
+
+/* Radiotap header iteration
+ * implemented in net/wireless/radiotap.c
+ *
+ * call __ieee80211_radiotap_iterator_init() to init the opaque iterator
+ * (no need to init anything in there beforehand)
+ * then loop calling __ieee80211_radiotap_iterator_next()... it returns -1
+ * if there are no more args in the header, or the next argument type index
+ * that is present. The iterator's this_arg member points to the start of the
+ * argument associated with the current argument type that is present,
+ * which can be found in the iterator's this_arg_index member.
+ */
+
+struct ieee80211_radiotap_iterator {
+ struct ieee80211_radiotap_header *rtheader;
+ int max_length; /* copy of max length we can scan over */
+ int this_arg_index; /* IEEE80211_RADIOTAP_* index for caller */
+ u8 * this_arg; /* current arg start position, caller can change */
+
+ int arg_index; /* internal: arg index b0 of bitmap_shifter represents */
+ u8 * arg; /* internal: points to the next arg start position */
+ __le32 *next_bitmap; /* internal */
+ u32 bitmap_shifter; /* internal */
+};
+
+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;
diff --git a/include/net/ieee80211_radiotap.h b/include/net/ieee80211_radiotap.h
index 7dbf9fb..b73c665 100644
--- a/include/net/ieee80211_radiotap.h
+++ b/include/net/ieee80211_radiotap.h
@@ -59,6 +59,9 @@
* use sufficiently weaselly language ("is a monotonically nondecreasing
* function of...") that I cannot set false expectations for lawyerly
* readers.
+ *
+ * All arguments and fields in the struct at the start are
+ * Little-endian
*/
/* XXX tcpdump/libpcap do not tolerate variable-length headers,
@@ -90,6 +93,8 @@ struct ieee80211_radiotap_header {
*/
};
+#define IEEE80211_RADIOTAP_PRESENT_EXTEND_MASK 0x80000000
+
/* Name Data type Units
* ---- --------- -----
*
@@ -230,4 +235,7 @@ enum ieee80211_radiotap_type {
(((x) == 14) ? 2484 : ((x) * 5) + 2407) : \
((x) + 1000) * 5)
-#endif /* IEEE80211_RADIOTAP_H */
+#endif
+
+
+/* IEEE80211_RADIOTAP_H */
diff --git a/net/wireless/Makefile b/net/wireless/Makefile
index 507a028..26f815a 100644
--- a/net/wireless/Makefile
+++ b/net/wireless/Makefile
@@ -1,6 +1,6 @@
obj-$(CONFIG_CFG80211) += cfg80211.o
-cfg80211-y += core.o sysfs.o
+cfg80211-y += core.o sysfs.o radiotap.o
cfg80211-$(CONFIG_NL80211) += nl80211.o
cfg80211-$(CONFIG_CFG80211_WEXT_COMPAT) += wext-compat.o
diff --git a/net/wireless/radiotap.c b/net/wireless/radiotap.c
new file mode 100644
index 0000000..2275e8e
--- /dev/null
+++ b/net/wireless/radiotap.c
@@ -0,0 +1,213 @@
+/*
+ * Radiotap parser
+ *
+ * Copyright 2007 Andy Green <andy@xxxxxxxxxxx>
+ */
+
+#include <linux/if.h>
+#include <linux/err.h>
+#include <linux/mutex.h>
+#include <linux/device.h>
+#include <net/genetlink.h>
+#include <net/cfg80211.h>
+#include <net/wireless.h>
+#include "nl80211.h"
+#include "core.h"
+#include <net/ieee80211_radiotap.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 on success or negative if sanity check fails
+ *
+ * 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.
+ */
+
+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(radiotap_header->it_len)))
+ return -EINVAL;
+
+ iterator->rtheader = radiotap_header;
+ iterator->max_length = le16_to_cpu(radiotap_header->it_len);
+ iterator->arg_index = 0;
+ iterator->bitmap_shifter = le32_to_cpu(radiotap_header->it_present);
+ iterator->arg = ((u8 *)radiotap_header) +
+ sizeof(struct ieee80211_radiotap_header);
+ iterator->this_arg = 0;
+
+ /* find payload start allowing for extended bitmap(s) */
+
+ if (iterator->bitmap_shifter & IEEE80211_RADIOTAP_PRESENT_EXTEND_MASK) {
+ while (le32_to_cpu(*((u32 *)iterator->arg)) &
+ IEEE80211_RADIOTAP_PRESENT_EXTEND_MASK)
+ iterator->arg += sizeof(u32);
+ iterator->arg += sizeof(u32);
+ }
+
+ /* 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: next present arg index on success or negative if no more or error
+ *
+ * This function returns the next radiotap arg index (IEEE80211_RADIOTAP_*)
+ * and sets iterator->this_arg to point to the payload for the arg. It takes
+ * care of alignment handling and extended present fields. interator->this_arg
+ * can be changed by the caller. The args pointed to are in little-endian
+ * format.
+ */
+
+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;
+
+ 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.
+ */
+
+ if ((((int)iterator->arg)-((int)iterator->rtheader)) &
+ ((rt_sizes[iterator->arg_index] >> 4) - 1))
+ iterator->arg_index +=
+ (rt_sizes[iterator->arg_index] >> 4) -
+ ((((int)iterator->arg) -
+ ((int)iterator->rtheader)) &
+ ((rt_sizes[iterator->arg_index] >> 4) - 1));
+
+ /* 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((((int)iterator->arg) - ((int)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(
+ *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 iterator->this_arg_index;
+
+ }
+
+ /* we don't know how to handle any more args, we're done */
+
+ return -1;
+}
+
+EXPORT_SYMBOL(ieee80211_radiotap_iterator_next);
+
--
-
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