[PATCH Try#12 0/3] Radiotap injection for Monitor Mode

[PATCH Try#12 0/3] Radiotap injection for Monitor Mode

[andy]

These patches add the ability to inject packets down a monitor mode interface for 
transmission according to a prepended radiotap header.

For injecting packets, the you issue a packet using libpcap or a SOCK_PACKET
socket down an interface to the wireless device that is in Monitor Mode.  The packet
has a normal radiotap header prepended to the IEEE80211 header.  The radiotap header
is variable length depending on what the user wants to specify, currently the
transmit rate, power and antenna can be specified using normal radiotap semantics.
Any other entries are skipped.

The radiotap parser is broken out into its own file under cfg80211.

A usermode app packetspammer is available from here

http://penumbra.warmcat.com/_twk/tiki-index.php?page=packetspammer

which allows easy injection of these packets from the commandline.  At the moment it
loops issuing packets at a variety of rates which can be seen from another
machine's monitor mode interface on the same channel.  There are instructions for
build and using it on the page above along with Fedora 7 binary and source RPMS.
There is now also a -f switch to allow testing of the FCS flag on injected packets.

Currently it has been tested for both rx and tx using zd1211rw-mac80211.

The patches are based against current wireless-dev.

I also added some documentation files which explains how to use the injection
functionality and radiotap header notes.
--  

[PATCH Try#12 1/3] mac80211: Monitor mode radiotap injection docs

[andy]

CC: John Linville <linville@tuxdriver.com>
CC: Johannes Berg <johannes@sipsolutions.net>
CC: Jiri Benc <jbenc@suse.cz>
Signed-off-by: Andy Green <andy@warmcat.com>


---
 Documentation/networking/mac80211-injection.txt |   59 +++++++++++++++++
 Documentation/networking/radiotap-headers.txt   |   79 ++++++++++++++++++++++++
 2 files changed, 138 insertions(+)

Index: wireless-dev/Documentation/networking/mac80211-injection.txt
===================================================================
--- /dev/null
+++ wireless-dev/Documentation/networking/mac80211-injection.txt
@@ -0,0 +1,59 @@
+How to use packet injection with mac80211
+=========================================
+
+mac80211 now allows arbitrary packets to be injected down any Monitor Mode
+interface from userland.  The packet you inject needs to be composed in the
+following format:
+
+ [ radiotap header  ]
+ [ ieee80211 header ]
+ [ payload ]
+
+The radiotap format is discussed in
+./Documentation/networking/radiotap-headers.txt.
+
+Despite 13 radiotap argument types are currently defined, most only make sense
+to appear on received packets.  Currently three kinds of argument are used by
+the injection code, although it knows to skip any other arguments that are
+present (facilitating replay of captured radiotap headers directly):
+
+ - IEEE80211_RADIOTAP_RATE - u8 arg in 500kbps units (0x02 --> 1Mbps)
+
+ - IEEE80211_RADIOTAP_ANTENNA - u8 arg, 0x00 = ant1, 0x01 = ant2
+
+ - IEEE80211_RADIOTAP_DBM_TX_POWER - u8 arg, dBm
+
+Here is an example valid radiotap header defining these three parameters
+
+	0x00, 0x00, // <-- radiotap version
+	0x0b, 0x00, // <- radiotap header length
+	0x04, 0x0c, 0x00, 0x00, // <-- bitmap
+	0x6c, // <-- rate
+	0x0c, //<-- tx power
+	0x01 //<-- antenna
+
+The ieee80211 header follows immediately afterwards, looking for example like
+this:
+
+	0x08, 0x01, 0x00, 0x00,
+	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+	0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
+	0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
+	0x10, 0x86
+
+Then lastly there is the payload.
+
+After composing the packet contents, it is sent by send()-ing it to a logical
+mac80211 interface that is in Monitor mode.  Libpcap can also be used,
+(which is easier than doing the work to bind the socket to the right
+interface), along the following lines:
+
+	ppcap = pcap_open_live(szInterfaceName, 800, 1, 20, szErrbuf);
+...
+	r = pcap_inject(ppcap, u8aSendBuffer, nLength);
+
+You can also find sources for a complete inject test applet here:
+
+http://penumbra.warmcat.com/_twk/tiki-index.php?page=packetspammer
+
+Andy Green <andy@warmcat.com>
Index: wireless-dev/Documentation/networking/radiotap-headers.txt
===================================================================
--- /dev/null
+++ wireless-dev/Documentation/networking/radiotap-headers.txt
@@ -0,0 +1,79 @@
+How to use radiotap headers
+===========================
+
+Pointer to the radiotap include file
+------------------------------------
+
+Radiotap headers are variable-length and extensible, you can get most of the
+information you need to know on them from:
+
+./include/net/ieee80211_radiotap.h
+
+This document gives an overview and warns on some corner cases.
+
+
+Structure of the header
+-----------------------
+
+There is a fixed portion at the start which contains a u32 bitmap that defines
+if the possible argument associated with that bit is present or not.  So if b0
+of the it_present member of ieee80211_radiotap_header is set, it means that
+the header for argument index 0 (IEEE80211_RADIOTAP_TSFT) is present in the
+argument area.
+
+   < 8-byte ieee80211_radiotap_header >
+   [ <possible argument bitmap extensions ... > ]
+   [ <argument> ... ]
+
+At the moment there are only 13 possible argument indexes defined, but in case
+we run out of space in the u32 it_present member, it is defined that b31 set
+indicates that there is another u32 bitmap following (shown as "possible
+argument bitmap extensions..." above), and the start of the arguments is moved
+forward 4 bytes each time.
+
+Note also that the it_len member __le16 is set to the total number of bytes
+covered by the ieee80211_radiotap_header and any arguments following.
+
+
+Requirements for arguments
+--------------------------
+
+After the fixed part of the header, the arguments follow for each argument
+index whose matching bit is set in the it_present member of
+ieee80211_radiotap_header.
+
+ - the arguments are all stored little-endian!
+
+ - the argument payload for a given argument index has a fixed size.  So
+   IEEE80211_RADIOTAP_TSFT being present always indicates an 8-byte argument is
+   present.  See the comments in ./include/net/ieee80211_radiotap.h for a nice
+   breakdown of all the argument sizes
+
+ - the arguments must be aligned to a boundary of the argument size using
+   padding.  So a u16 argument must start on the next u16 boundary if it isn't
+   already on one, a u32 must start on the next u32 boundary and so on.
+
+ - "alignment" is relative to the start of the ieee80211_radiotap_header, ie,
+   the first byte of the radiotap header.  The absolute alignment of that first
+   byte isn't defined.  So even if the whole radiotap header is starting at, eg,
+   address 0x00000003, still the first byte of the radiotap header is treated as
+   0 for alignment purposes.
+
+ - The arguments for a given argument index can be a compound of multiple types
+   together.  For example IEEE80211_RADIOTAP_CHANNEL has an argument payload
+   consisting of two u16s of total length 4.  When this happens, the padding
+   rule is applied dealing with a u16, NOT dealing with a 4-byte single entity.
+
+
+Example valid radiotap header
+-----------------------------
+
+	0x00, 0x00, // <-- radiotap version + pad byte
+	0x0b, 0x00, // <- radiotap header length
+	0x04, 0x0c, 0x00, 0x00, // <-- bitmap
+	0x6c, // <-- rate (in 500kHz units)
+	0x0c, //<-- tx power
+	0x01 //<-- antenna
+
+
+Andy Green <andy@warmcat.com>

-- 

[PATCH Try#12 2/3] cfg80211: Radiotap parser

[andy]

Generic code to walk through the fields in a radiotap header, accounting
for nasties like extended "field present" bitfields and alignment rules

Try #12  comments from Michael Wu
 - Use 1<<IEEE80211_RADIOTAP_EXT then no need to add mask to radiotap hdr
 - Revert Johannes' enum method
 - break down padding action with temp var

Try #11
 - parser returns enum retcode - Johannes Berg

Try #10  comments from Michael Wu
 - kill some spaces between * and var/arg
 - weed out cut-n-pasted #includes that aren't actually used
 - kill vertical justification
 - kill unneccessary parenthesis in some expressions
 - sizeof() on dereferenced vars not types
 - ulong pointer arithmetic!  Good catch!

Try #9 (of the radiotap patchset) thanks to Johannes Berg's feedback
 - Add docs to nano kernel docs
 - Add docs to Documentation/networking/radiotap-headers.txt
 - Fix typos

Try #2
 - added sanity check to extended present bitmap u32 walking code - disallow
   possibility to walk past the end of the radiotap header length

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).

CC: John Linville <linville@tuxdriver.com>
CC: Johannes Berg <johannes@sipsolutions.net>
CC: Jiri Benc <jbenc@suse.cz>
Signed-off-by: Andy Green <andy@warmcat.com>

===================================================

---
 Documentation/networking/radiotap-headers.txt |   59 ++++++
 include/net/cfg80211.h                        |   38 ++++
 net/wireless/Makefile                         |    2 
 net/wireless/radiotap.c                       |  243 ++++++++++++++++++++++++++
 4 files changed, 341 insertions(+), 1 deletion(-)

Index: wireless-dev/include/net/cfg80211.h
===================================================================
--- wireless-dev.orig/include/net/cfg80211.h
+++ wireless-dev/include/net/cfg80211.h
@@ -74,6 +74,44 @@ struct key_params {
 	u32 cipher;
 };
 
+
+/* 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;
 
Index: wireless-dev/net/wireless/Makefile
===================================================================
--- wireless-dev.orig/net/wireless/Makefile
+++ wireless-dev/net/wireless/Makefile
@@ -1,5 +1,5 @@
 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
 cfg80211-$(CONFIG_NL80211) += nl80211.o
Index: wireless-dev/net/wireless/radiotap.c
===================================================================
--- /dev/null
+++ wireless-dev/net/wireless/radiotap.c
@@ -0,0 +1,243 @@
+/*
+ * Radiotap parser
+ *
+ * Copyright 2007		Andy Green <andy@warmcat.com>
+ */
+
+#include <net/cfg80211.h>
+#include <net/ieee80211_radiotap.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.
+ *
+ * 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(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(*radiotap_header);
+	iterator->this_arg = 0;
+
+	/* find payload start allowing for extended bitmap(s) */
+
+	if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) {
+		while (le32_to_cpu(*(u32 *)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.
+ */
+
+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.
+		 */
+
+		pad = (((ulong)iterator->arg) -
+			((ulong)iterator->rtheader)) &
+			((rt_sizes[iterator->arg_index] >> 4) - 1);
+
+		if (pad)
+			iterator->arg_index +=
+				(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(*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);
Index: wireless-dev/Documentation/networking/radiotap-headers.txt
===================================================================
--- wireless-dev.orig/Documentation/networking/radiotap-headers.txt
+++ wireless-dev/Documentation/networking/radiotap-headers.txt
@@ -76,4 +76,63 @@ 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) {
+		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>

-- 

[PATCH Try#12 3/3] mac80211: Monitor mode radiotap-based packet injection

[andy]

Try #12 Comments from Michael Wu
 - Revert enum retcode stuff
 - Handle flags, checking if FCS marked as present and snipping it
 - kill a blank line

Try #11
 - Change parser loop code around to deal with enum retcodes

Try #10  Comments from Michael Wu
 - __ieee80211_convert_radiotap_to_control_and_remove ->
   __ieee80211_parse_tx_radiotap
 - death to vertical justification
 - -ve to negative
 - struct ieee80211_hw_mode should be called "mode" by convention

Try #9
 - Normalize multiline comment style

Try #6
 - Accounted for various comments from Johannes Berg
 - Radiotap parsing is moved to cfg80211 as requested in a separate patch

Try #5
 - De-indent last few indented comments

Try #4
 - All from Michael Wu's feedback: further style heresies removed
 - took account of radiotap arg alignment requirement.  n-byte arg must be
   placed on n-byte boundary using padding where necessary

Try #3
 - moved to Michael Wu's method of tracking if we came in on a
   monitor interface by using ifindex
 - removed older proposed monitor interface tracking method and flags
 - style fixes
 - removed duped #include that is present in Michael Wu's patch already

Try #2
 - took Michael Wu's advice about better tools and basing on wireless-dev
 - took Luis Rodriguez's advice about coding style makeover
 - took Pavel Roskin's advice about little-endian radiotap

CC: John Linville <linville@tuxdriver.com>
CC: Johannes Berg <johannes@sipsolutions.net>
CC: Jiri Benc <jbenc@suse.cz>
Signed-off-by: Andy Green <andy@warmcat.com>


---
 net/mac80211/ieee80211.c |  225 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 215 insertions(+), 10 deletions(-)

Index: wireless-dev/net/mac80211/ieee80211.c
===================================================================
--- wireless-dev.orig/net/mac80211/ieee80211.c
+++ wireless-dev/net/mac80211/ieee80211.c
@@ -1118,7 +1118,132 @@ ieee80211_tx_h_ps_buf(struct ieee80211_t
 }
 
 
-static void inline
+/*
+ * deal with packet injection down monitor interface
+ * with Radiotap Header -- only called for monitor mode interface
+ */
+
+static ieee80211_txrx_result
+__ieee80211_parse_tx_radiotap(
+	struct ieee80211_txrx_data *tx,
+	struct sk_buff *skb, struct ieee80211_tx_control *control)
+{
+	/*
+	 * this is the moment to interpret and discard the radiotap header that
+	 * must be at the start of the packet injected in Monitor mode
+	 *
+	 * Need to take some care with endian-ness since radiotap
+	 * args are little-endian
+	 */
+
+	struct ieee80211_radiotap_iterator iterator;
+	struct ieee80211_radiotap_header *rthdr =
+		(struct ieee80211_radiotap_header *) skb->data;
+	struct ieee80211_hw_mode *mode = tx->local->hw.conf.mode;
+	int ret = ieee80211_radiotap_iterator_init(&iterator, rthdr, skb->len);
+
+	/*
+	 * default control situation for all injected packets
+	 * FIXME: this does not suit all usage cases, expand to allow control
+	 */
+
+	control->retry_limit = 1; /* no retry */
+	control->key_idx = -1; /* no encryption key */
+	control->flags &= ~(IEEE80211_TXCTL_USE_RTS_CTS |
+			    IEEE80211_TXCTL_USE_CTS_PROTECT);
+	control->flags |= IEEE80211_TXCTL_DO_NOT_ENCRYPT |
+			  IEEE80211_TXCTL_NO_ACK;
+	control->antenna_sel_tx = 0; /* default to default antenna */
+
+	/*
+	 * for every radiotap entry that is present
+	 * (ieee80211_radiotap_iterator_next returns -ENOENT when no more
+	 * entries present, or -EINVAL on error)
+	 */
+
+	while (!ret) {
+		int i, target_rate;
+
+	 	ret = ieee80211_radiotap_iterator_next(&iterator);
+
+		if (ret)
+			continue;
+
+		/* see if this argument is something we can use */
+		switch (iterator.this_arg_index) {
+		case IEEE80211_RADIOTAP_RATE:
+			/*
+			 * radiotap rate u8 is in 500kbps units eg, 0x02=1Mbps
+			 * ieee80211 rate int is in 100kbps units eg, 0x0a=1Mbps
+			 */
+			target_rate = (*iterator.this_arg) * 5;
+			for (i = 0; i < mode->num_rates; i++) {
+				struct ieee80211_rate *r = &mode->rates[i];
+
+				if (r->rate > target_rate)
+					continue;
+
+				control->rate = r;
+
+				if (r->flags & IEEE80211_RATE_PREAMBLE2)
+					control->tx_rate = r->val2;
+				else
+					control->tx_rate = r->val;
+
+				/* end on exact match */
+				if (r->rate == target_rate)
+					i = mode->num_rates;
+			}
+			break;
+
+		case IEEE80211_RADIOTAP_ANTENNA:
+			/*
+			 * radiotap uses 0 for 1st ant, mac80211 is 1 for
+			 * 1st ant
+			 */
+			control->antenna_sel_tx = (*iterator.this_arg) + 1;
+			break;
+
+		case IEEE80211_RADIOTAP_DBM_TX_POWER:
+			control->power_level = *iterator.this_arg;
+			break;
+
+		case IEEE80211_RADIOTAP_FLAGS:
+			if (*iterator.this_arg & IEEE80211_RADIOTAP_F_FCS) {
+				/*
+				 * this indicates that the skb we have been
+				 * handed has the 32-bit FCS CRC at the end...
+				 * we should react to that by snipping it off
+				 * because it will be recomputed and added
+				 * on transmission
+				 */
+				if (skb->len < (iterator.max_length + FCS_LEN))
+					return TXRX_DROP;
+
+				skb_trim(skb, skb->len - FCS_LEN);
+			}
+			break;
+
+		default:
+			break;
+		}
+	}
+
+	if (ret != -ENOENT) /* ie, if we didn't simply run out of fields */
+		return TXRX_DROP;
+
+	/*
+	 * remove the radiotap header
+	 * iterator->max_length was sanity-checked against
+	 * skb->len by iterator init
+	 */
+	skb_pull(skb, iterator.max_length);
+
+	return TXRX_CONTINUE;
+}
+
+
+static ieee80211_txrx_result inline
 __ieee80211_tx_prepare(struct ieee80211_txrx_data *tx,
 		       struct sk_buff *skb,
 		       struct net_device *dev,
@@ -1126,6 +1251,9 @@ __ieee80211_tx_prepare(struct ieee80211_
 {
 	struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
+	struct ieee80211_sub_if_data *sdata;
+	ieee80211_txrx_result res = TXRX_CONTINUE;
+
 	int hdrlen;
 
 	memset(tx, 0, sizeof(*tx));
@@ -1135,7 +1263,32 @@ __ieee80211_tx_prepare(struct ieee80211_
 	tx->sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 	tx->sta = sta_info_get(local, hdr->addr1);
 	tx->fc = le16_to_cpu(hdr->frame_control);
+
+	/*
+	 * set defaults for things that can be set by
+	 * injected radiotap headers
+	 */
 	control->power_level = local->hw.conf.power_level;
+	control->antenna_sel_tx = local->hw.conf.antenna_sel_tx;
+	if (local->sta_antenna_sel != STA_ANTENNA_SEL_AUTO && tx->sta)
+		control->antenna_sel_tx = tx->sta->antenna_sel_tx;
+
+	/* process and remove the injection radiotap header */
+	sdata = IEEE80211_DEV_TO_SUB_IF(dev);
+	if (unlikely(sdata->type == IEEE80211_IF_TYPE_MNTR)) {
+		if (__ieee80211_parse_tx_radiotap(tx, skb, control) ==
+								TXRX_DROP) {
+			return TXRX_DROP;
+		}
+		/*
+		 * we removed the radiotap header after this point,
+		 * we filled control with what we could use
+		 * set to the actual ieee header now
+		 */
+		hdr = (struct ieee80211_hdr *) skb->data;
+		res = TXRX_QUEUED; /* indication it was monitor packet */
+	}
+
 	tx->u.tx.control = control;
 	tx->u.tx.unicast = !is_multicast_ether_addr(hdr->addr1);
 	if (is_multicast_ether_addr(hdr->addr1))
@@ -1152,9 +1305,6 @@ __ieee80211_tx_prepare(struct ieee80211_
 		control->flags |= IEEE80211_TXCTL_CLEAR_DST_MASK;
 		tx->sta->clear_dst_mask = 0;
 	}
-	control->antenna_sel_tx = local->hw.conf.antenna_sel_tx;
-	if (local->sta_antenna_sel != STA_ANTENNA_SEL_AUTO && tx->sta)
-		control->antenna_sel_tx = tx->sta->antenna_sel_tx;
 	hdrlen = ieee80211_get_hdrlen(tx->fc);
 	if (skb->len > hdrlen + sizeof(rfc1042_header) + 2) {
 		u8 *pos = &skb->data[hdrlen + sizeof(rfc1042_header)];
@@ -1162,6 +1312,7 @@ __ieee80211_tx_prepare(struct ieee80211_
 	}
 	control->flags |= IEEE80211_TXCTL_FIRST_FRAGMENT;
 
+	return res;
 }
 
 static int inline is_ieee80211_device(struct net_device *dev,
@@ -1274,7 +1425,7 @@ static int ieee80211_tx(struct net_devic
 	struct sta_info *sta;
 	ieee80211_tx_handler *handler;
 	struct ieee80211_txrx_data tx;
-	ieee80211_txrx_result res = TXRX_DROP;
+	ieee80211_txrx_result res = TXRX_DROP, res_prepare;
 	int ret, i;
 
 	WARN_ON(__ieee80211_queue_pending(local, control->queue));
@@ -1284,15 +1435,26 @@ static int ieee80211_tx(struct net_devic
 		return 0;
 	}
 
-	__ieee80211_tx_prepare(&tx, skb, dev, control);
+	res_prepare = __ieee80211_tx_prepare(&tx, skb, dev, control);
+
+	if (res_prepare == TXRX_DROP) {
+		dev_kfree_skb(skb);
+		return 0;
+	}
+
 	sta = tx.sta;
 	tx.u.tx.mgmt_interface = mgmt;
 	tx.u.tx.mode = local->hw.conf.mode;
 
-	for (handler = local->tx_handlers; *handler != NULL; handler++) {
-		res = (*handler)(&tx);
-		if (res != TXRX_CONTINUE)
-			break;
+	if (res_prepare == TXRX_QUEUED) { /* if it was an injected packet */
+		res = TXRX_CONTINUE;
+	} else {
+		for (handler = local->tx_handlers; *handler != NULL;
+		     handler++) {
+			res = (*handler)(&tx);
+			if (res != TXRX_CONTINUE)
+				break;
+		}
 	}
 
 	skb = tx.skb; /* handlers are allowed to change skb */
@@ -1531,6 +1693,49 @@ static int ieee80211_subif_start_xmit(st
 		goto fail;
 	}
 
+	if (unlikely(sdata->type == IEEE80211_IF_TYPE_MNTR)) {
+		struct ieee80211_radiotap_header * prthdr =
+			(struct ieee80211_radiotap_header *)skb->data;
+
+		/*
+		 * there must be a radiotap header at the
+		 * start in this case
+		 */
+		if (unlikely(prthdr->it_version)) {
+			/* only version 0 is supported  */
+			ret = 0;
+			goto fail;
+		}
+
+		skb->dev = local->mdev;
+
+		pkt_data = (struct ieee80211_tx_packet_data *)skb->cb;
+		memset(pkt_data, 0, sizeof(*pkt_data));
+		pkt_data->ifindex = sdata->dev->ifindex;
+		pkt_data->mgmt_iface = 0;
+		pkt_data->do_not_encrypt = 1;
+
+		/* above needed because we set skb device to master */
+
+		/*
+		 * fix up the pointers accounting for the radiotap
+		 * header still being in there.  We are being given
+		 * a precooked IEEE80211 header so no need for
+		 * normal processing
+		 */
+		skb_set_mac_header(skb, prthdr->it_len);
+		skb_set_network_header(skb, prthdr->it_len + sizeof(hdr));
+		skb_set_transport_header(skb, prthdr->it_len + sizeof(hdr));
+
+		/*
+		 * pass the radiotap header up to
+		 * the next stage intact
+		 */
+		dev_queue_xmit(skb);
+
+		return 0;
+	}
+
 	nh_pos = skb_network_header(skb) - skb->data;
 	h_pos = skb_transport_header(skb) - skb->data;
 

-- 

Re: [PATCH Try#12 2/3] cfg80211: Radiotap parser

[Johannes Berg]

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Hi Andy,

Sorry, I really hate doing this, but I found yet another problem :/

Hi Andy,

Sorry, I really hate having comments again and again but never really
thought about this earlier, the FCS removal thing you added made me
think...


> + * @max_length: total length we can parse into (eg, whole packet length)

> +	/* sanity check for allowed length and radiotap length field */
> +	if (max_length < le16_to_cpu(radiotap_header->it_len))
> +		return -EINVAL;

> +	iterator->max_length = le16_to_cpu(radiotap_header->it_len);

This is fine, at first sight, but if you let the caller modify the skb
like mac80211 now does with stripping the FCS, the max length really
needs to be passed to each invocation of
ieee80211_radiotap_iterator_next in order to catch invalid skbs. Mind
you, we wouldn't Oops since trimming just moves the skb tail pointer,
but something that indicated a longer length and then just have a packet
like

0x00, 0x00, // <-- radiotap version
0x08, 0x00, // <- radiotap header length
0x10, 0x00, 0x00, 0x00, // <-- bitmap, FCS bit set

which might not do the right thing and it'd be better IMHO to catch it
explicitly.

Also related to FCS, if you respin I think I'd like to have an explicit
"0x00" entry in rt_sizes for it so it's obvious that it's intentionally
0, otherwise I'll post a patch after the code goes in.

Another question: since there's no alignment requirement for the skb
that contains the radiotap header, I think you need something like

iterator->bitmap_shifter = 
	le32_to_cpu(get_unaligned(iterator->next_bitmap))

instead of

> +                               iterator->bitmap_shifter =
> +                                   le32_to_cpu(*iterator->next_bitmap);

in many places.

johannes

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Re: [PATCH Try#12 3/3] mac80211: Monitor mode radiotap-based packet injection

[Johannes Berg]

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On Wed, 2007-06-13 at 10:37 +0100, andy@warmcat.com wrote:

> +	control->flags &= ~(IEEE80211_TXCTL_USE_RTS_CTS |
> +			    IEEE80211_TXCTL_USE_CTS_PROTECT);

> +		case IEEE80211_RADIOTAP_FLAGS:

I suppose that IEEE80211_RADIOTAP_TX_FLAGS and
IEEE80211_RADIOTAP_F_TX_CTS and IEEE80211_RADIOTAP_F_TX_RTS could be
supported as well...

Also IEEE80211_RADIOTAP_F_SHORTPRE and IEEE80211_RADIOTAP_F_DATAPAD
(though we never generate frames with that afaik) ought to be
possible...

However: *please don't do it now*. This mail is mainly meant as a note
to myself to do it (unless somebody else wants to do it...), adding it
now would probably open discussion on the patches again and we'll never
finish...

johannes

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Re: [PATCH Try#12 0/3] Radiotap injection for Monitor Mode

[Michael Wu]

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On Wednesday 13 June 2007 02:37, andy@warmcat.com wrote:
> These patches add the ability to inject packets down a monitor mode
> interface for transmission according to a prepended radiotap header.
>
I've attached a patch to address remaining issues found by git, sparse, and 
checkpatch.pl. With that, ACK.

Thanks,
-Michael Wu

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mac80211: radiotap injection code sparse/style fixes

From: Michael Wu <flamingice@sourmilk.net>

This fixes the remaining issues in the radiotap code found by git, sparse,
and checkpatch.pl. (and one last space between * and variable name found
by myself.)

Signed-off-by: Michael Wu <flamingice@sourmilk.net>
---

 Documentation/networking/radiotap-headers.txt |    2 +-
 net/mac80211/ieee80211.c                      |   12 +++++++-----
 net/wireless/radiotap.c                       |    6 ++----
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/Documentation/networking/radiotap-headers.txt b/Documentation/networking/radiotap-headers.txt
index 5148075..bd846de 100644
--- a/Documentation/networking/radiotap-headers.txt
+++ b/Documentation/networking/radiotap-headers.txt
@@ -95,7 +95,7 @@ int MyFunction(u8 * buf, int buflen)
 
 	while (!ret) {
 
-	 	ret = ieee80211_radiotap_iterator_next(&iterator);
+		ret = ieee80211_radiotap_iterator_next(&iterator);
 
 		if (ret)
 			continue;
diff --git a/net/mac80211/ieee80211.c b/net/mac80211/ieee80211.c
index 5f2bf3e..023aa18 100644
--- a/net/mac80211/ieee80211.c
+++ b/net/mac80211/ieee80211.c
@@ -1164,7 +1164,7 @@ __ieee80211_parse_tx_radiotap(
 	while (!ret) {
 		int i, target_rate;
 
-	 	ret = ieee80211_radiotap_iterator_next(&iterator);
+		ret = ieee80211_radiotap_iterator_next(&iterator);
 
 		if (ret)
 			continue;
@@ -1694,8 +1694,9 @@ static int ieee80211_subif_start_xmit(struct sk_buff *skb,
 	}
 
 	if (unlikely(sdata->type == IEEE80211_IF_TYPE_MNTR)) {
-		struct ieee80211_radiotap_header * prthdr =
+		struct ieee80211_radiotap_header *prthdr =
 			(struct ieee80211_radiotap_header *)skb->data;
+		u16 len;
 
 		/*
 		 * there must be a radiotap header at the
@@ -1723,9 +1724,10 @@ static int ieee80211_subif_start_xmit(struct sk_buff *skb,
 		 * a precooked IEEE80211 header so no need for
 		 * normal processing
 		 */
-		skb_set_mac_header(skb, prthdr->it_len);
-		skb_set_network_header(skb, prthdr->it_len + sizeof(hdr));
-		skb_set_transport_header(skb, prthdr->it_len + sizeof(hdr));
+		len = le16_to_cpu(prthdr->it_len);
+		skb_set_mac_header(skb, len);
+		skb_set_network_header(skb, len + sizeof(hdr));
+		skb_set_transport_header(skb, len + sizeof(hdr));
 
 		/*
 		 * pass the radiotap header up to
diff --git a/net/wireless/radiotap.c b/net/wireless/radiotap.c
index 1b4a7be..091f234 100644
--- a/net/wireless/radiotap.c
+++ b/net/wireless/radiotap.c
@@ -60,12 +60,12 @@ int ieee80211_radiotap_iterator_init(
 	iterator->arg_index = 0;
 	iterator->bitmap_shifter = le32_to_cpu(radiotap_header->it_present);
 	iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header);
-	iterator->this_arg = 0;
+	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(*(u32 *)iterator->arg) &
+		while (le32_to_cpu(*(__le32 *)iterator->arg) &
 				   (1<<IEEE80211_RADIOTAP_EXT)) {
 			iterator->arg += sizeof(u32);
 
@@ -93,7 +93,6 @@ int ieee80211_radiotap_iterator_init(
 
 	return 0;
 }
-
 EXPORT_SYMBOL(ieee80211_radiotap_iterator_init);
 
 
@@ -239,5 +238,4 @@ int ieee80211_radiotap_iterator_next(
 	/* 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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Re: [PATCH Try#12 0/3] Radiotap injection for Monitor Mode

[Andy Green]

Michael Wu wrote:
> On Wednesday 13 June 2007 02:37, andy@warmcat.com wrote:
>> These patches add the ability to inject packets down a monitor mode
>> interface for transmission according to a prepended radiotap header.
>>
> I've attached a patch to address remaining issues found by git, sparse, and 
> checkpatch.pl. With that, ACK.

Thanks for all the work you and Johannes put in with review and bug finding.

-Andy

Re: [PATCH Try#12 2/3] cfg80211: Radiotap parser

[Johannes Berg]

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On Wed, 2007-06-13 at 20:47 +0200, Johannes Berg wrote:
> Hi Andy,
> 
> Sorry, I really hate doing this, but I found yet another problem :/
> 
> Hi Andy,
> 
> Sorry, I really hate having comments again and again but never really
> thought about this earlier, the FCS removal thing you added made me
> think...

/me is confused. when did I write *that* mail? Heh.

johannes

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Re: [PATCH Try#12 2/3] cfg80211: Radiotap parser

[Andy Green]

Johannes Berg wrote:
> Hi Andy,
> 
> Sorry, I really hate doing this, but I found yet another problem :/
> 
> Hi Andy,
> 
> Sorry, I really hate having comments again and again but never really
> thought about this earlier, the FCS removal thing you added made me
> think...
> 
> 
>> + * @max_length: total length we can parse into (eg, whole packet length)
> 
>> +	/* sanity check for allowed length and radiotap length field */
>> +	if (max_length < le16_to_cpu(radiotap_header->it_len))
>> +		return -EINVAL;
> 
>> +	iterator->max_length = le16_to_cpu(radiotap_header->it_len);
> 
> This is fine, at first sight, but if you let the caller modify the skb
> like mac80211 now does with stripping the FCS, the max length really
> needs to be passed to each invocation of
> ieee80211_radiotap_iterator_next in order to catch invalid skbs. Mind
> you, we wouldn't Oops since trimming just moves the skb tail pointer,
> but something that indicated a longer length and then just have a packet
> like

Hi Johannes -

No it sounds a real issue, don't feel bad!  I will look at it
thismorning and fold the changes from Michael into another try.

-Andy

Re: [PATCH Try#12 2/3] cfg80211: Radiotap parser

[Andy Green]

Johannes Berg wrote:

>> + * @max_length: total length we can parse into (eg, whole packet length)
> 
>> +	/* sanity check for allowed length and radiotap length field */
>> +	if (max_length < le16_to_cpu(radiotap_header->it_len))
>> +		return -EINVAL;
> 
>> +	iterator->max_length = le16_to_cpu(radiotap_header->it_len);
> 
> This is fine, at first sight, but if you let the caller modify the skb
> like mac80211 now does with stripping the FCS, the max length really
> needs to be passed to each invocation of
> ieee80211_radiotap_iterator_next in order to catch invalid skbs. Mind
> you, we wouldn't Oops since trimming just moves the skb tail pointer,

Looking at the code, I think this can be okay unless I didn't understand
your point.  At the time that the skb length is modified, I have this:

				if (skb->len < (iterator.max_length + FCS_LEN))
					return TXRX_DROP;

				skb_trim(skb, skb->len - FCS_LEN);

iterator.max_length is the claimed radiotap header total length, which
was verified to be within the original skb length already.  So at skb
length modification time, we take care beforehand that we have skb data
after the radiotap area to trim, otherwise we bail.  Trimming into the
radiotap header region would be a bug in the code calling the parser, so
we trust that if the radiotap header length fitted in the skb at the
start it does so during the parsing.

> but something that indicated a longer length and then just have a packet
> like
> 
> 0x00, 0x00, // <-- radiotap version
> 0x08, 0x00, // <- radiotap header length
> 0x10, 0x00, 0x00, 0x00, // <-- bitmap, FCS bit set
> 
> which might not do the right thing and it'd be better IMHO to catch it
> explicitly.

This case is explicitly captured here if we accept that any skb length
modification ensures that the original radiotap header length is left alone:

		/*
		 * 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;

> Also related to FCS, if you respin I think I'd like to have an explicit
> "0x00" entry in rt_sizes for it so it's obvious that it's intentionally
> 0, otherwise I'll post a patch after the code goes in.

I'm sorry I wasn't able to understand this.  FCS presence is a feature
of the IEEE80211_RADIOTAP_FLAGS radiotap entry which does have an entry
in rt_sizes?

> Another question: since there's no alignment requirement for the skb
> that contains the radiotap header, I think you need something like
> 
> iterator->bitmap_shifter = 
> 	le32_to_cpu(get_unaligned(iterator->next_bitmap))
> 
> instead of
> 
>> +                               iterator->bitmap_shifter =
>> +                                   le32_to_cpu(*iterator->next_bitmap);
> 
> in many places.

However this is a real objection I can understand :-/  Happens I
recently had experience of these alignment issues on mISDN for ARM,
although that has an (expensive) magic fixup exception handler some
arches, I was told Blackfin, don't.

I will have a go at fixing these and am interested in your take on the
other points.

-Andy

Re: [PATCH Try#12 2/3] cfg80211: Radiotap parser

[Johannes Berg]

[-- Attachment #1: Type: text/plain, Size: 1181 bytes --]

On Thu, 2007-06-14 at 11:02 +0100, Andy Green wrote:

> Looking at the code, I think this can be okay unless I didn't understand
> your point.  At the time that the skb length is modified, I have this:
> 
> 				if (skb->len < (iterator.max_length + FCS_LEN))
> 					return TXRX_DROP;
> 
> 				skb_trim(skb, skb->len - FCS_LEN);
> 
> iterator.max_length is the claimed radiotap header total length, which
> was verified to be within the original skb length already.  So at skb
> length modification time, we take care beforehand that we have skb data
> after the radiotap area to trim, otherwise we bail.  Trimming into the
> radiotap header region would be a bug in the code calling the parser, so
> we trust that if the radiotap header length fitted in the skb at the
> start it does so during the parsing.

Ah, I missed that, I was under the impression that the iterator_next
call was responsible for this error handling, but yeah, this is just
fine.

> I'm sorry I wasn't able to understand this.  FCS presence is a feature
> of the IEEE80211_RADIOTAP_FLAGS radiotap entry which does have an entry
> in rt_sizes?

Yeah, my mistake, sorry.

johannes

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