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| -rw-r--r-- | Documentation/networking/mac80211-injection.txt | 59 | ||||
| -rw-r--r-- | Documentation/networking/radiotap-headers.txt | 87 |
2 files changed, 146 insertions, 0 deletions
diff --git a/Documentation/networking/mac80211-injection.txt b/Documentation/networking/mac80211-injection.txt new file mode 100644 index 0000000..53ef7a0 --- /dev/null +++ b/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> diff --git a/Documentation/networking/radiotap-headers.txt b/Documentation/networking/radiotap-headers.txt new file mode 100644 index 0000000..e29e027 --- /dev/null +++ b/Documentation/networking/radiotap-headers.txt @@ -0,0 +1,87 @@ +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 above point that there may be no absolute alignment for multibyte + entities in the fixed radiotap header or the argument region means that you + have to take special evasive action when trying to access these multibyte + entities. Some arches like Blackfin cannot deal with an attempt to + dereference, eg, a u16 pointer that is pointing to an odd address. Instead + you have to use a kernel API get_unaligned() to dereference the pointer, + which will do it bytewise on the arches that require that. + + - 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> |
