1How to use packet injection with mac80211
2=========================================
3
4mac80211 now allows arbitrary packets to be injected down any Monitor Mode
5interface from userland.  The packet you inject needs to be composed in the
6following format:
7
8 [ radiotap header  ]
9 [ ieee80211 header ]
10 [ payload ]
11
12The radiotap format is discussed in
13./Documentation/networking/radiotap-headers.txt.
14
15Despite many radiotap parameters being currently defined, most only make sense
16to appear on received packets.  The following information is parsed from the
17radiotap headers and used to control injection:
18
19 * IEEE80211_RADIOTAP_FLAGS
20
21   IEEE80211_RADIOTAP_F_FCS: FCS will be removed and recalculated
22   IEEE80211_RADIOTAP_F_WEP: frame will be encrypted if key available
23   IEEE80211_RADIOTAP_F_FRAG: frame will be fragmented if longer than the
24			      current fragmentation threshold.
25
26 * IEEE80211_RADIOTAP_TX_FLAGS
27
28   IEEE80211_RADIOTAP_F_TX_NOACK: frame should be sent without waiting for
29				  an ACK even if it is a unicast frame
30
31The injection code can also skip all other currently defined radiotap fields
32facilitating replay of captured radiotap headers directly.
33
34Here is an example valid radiotap header defining some parameters
35
36	0x00, 0x00, // <-- radiotap version
37	0x0b, 0x00, // <- radiotap header length
38	0x04, 0x0c, 0x00, 0x00, // <-- bitmap
39	0x6c, // <-- rate
40	0x0c, //<-- tx power
41	0x01 //<-- antenna
42
43The ieee80211 header follows immediately afterwards, looking for example like
44this:
45
46	0x08, 0x01, 0x00, 0x00,
47	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
48	0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
49	0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
50	0x10, 0x86
51
52Then lastly there is the payload.
53
54After composing the packet contents, it is sent by send()-ing it to a logical
55mac80211 interface that is in Monitor mode.  Libpcap can also be used,
56(which is easier than doing the work to bind the socket to the right
57interface), along the following lines:
58
59	ppcap = pcap_open_live(szInterfaceName, 800, 1, 20, szErrbuf);
60...
61	r = pcap_inject(ppcap, u8aSendBuffer, nLength);
62
63You can also find a link to a complete inject application here:
64
65http://wireless.kernel.org/en/users/Documentation/packetspammer
66
67Andy Green <andy@warmcat.com>
68