From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mog.warmcat.com ([62.193.232.24]:49705 "EHLO mailserver.mog.warmcat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753585AbXCTKlH (ORCPT ); Tue, 20 Mar 2007 06:41:07 -0400 Received: from armbox7.home.warmcat.com (cpc1-nthc5-0-0-cust289.nrth.cable.ntl.com [82.29.29.34]) by mailserver.mog.warmcat.com (Postfix) with ESMTP id 17F148D125 for ; Tue, 20 Mar 2007 11:41:06 +0100 (CET) Received: from meerkat.home.warmcat.com (flatcat [192.168.0.77]) by armbox7.home.warmcat.com (Postfix) with ESMTP id 779CE10090 for ; Tue, 20 Mar 2007 10:41:08 +0000 (UTC) Message-Id: <20070320104104.575903961@warmcat.com> References: <20070320103955.600509703@warmcat.com> Date: Tue, 20 Mar 2007 10:39:58 +0000 From: andy@warmcat.com To: linux-wireless@vger.kernel.org Subject: [PATCH 3/4] mac80211: Monitor mode radiotap injection docs Sender: linux-wireless-owner@vger.kernel.org List-ID: From: Andy Green diff --git a/Documentation/networking/mac80211-injection.txt b/Documentation/networking/mac80211-injection.txt new file mode 100644 index 0000000..bee8931 --- /dev/null +++ b/Documentation/networking/mac80211-injection.txt @@ -0,0 +1,77 @@ +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 ] + +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 + +But note: all fields in the radiotap header are *little endian*. + +There is a fixed portion at the start which contains a u32 bitmap that defines +if the possible argument is present or not. At the moment there are only 13 +possible arguments defined, but in case we run out of space in the u32 it is +defined that b31 set indicates that there is another u32 bitmap following, and +the start of the arguments is moved forward 4 bytes each time. + +After the fixed part of the header, the arguments follow. + + - the arguments are all little-endian! + + - 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. + +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 --