1.. SPDX-License-Identifier: GPL-2.0
2
3=========================================
4How to use packet injection with mac80211
5=========================================
6
7mac80211 now allows arbitrary packets to be injected down any Monitor Mode
8interface from userland.  The packet you inject needs to be composed in the
9following format::
10
11 [ radiotap header  ]
12 [ ieee80211 header ]
13 [ payload ]
14
15The radiotap format is discussed in
16./Documentation/networking/radiotap-headers.rst.
17
18Despite many radiotap parameters being currently defined, most only make sense
19to appear on received packets.  The following information is parsed from the
20radiotap headers and used to control injection:
21
22 * IEEE80211_RADIOTAP_FLAGS
23
24   =========================  ===========================================
25   IEEE80211_RADIOTAP_F_FCS   FCS will be removed and recalculated
26   IEEE80211_RADIOTAP_F_WEP   frame will be encrypted if key available
27   IEEE80211_RADIOTAP_F_FRAG  frame will be fragmented if longer than the
28			      current fragmentation threshold.
29   =========================  ===========================================
30
31 * IEEE80211_RADIOTAP_TX_FLAGS
32
33   =============================  ========================================
34   IEEE80211_RADIOTAP_F_TX_NOACK  frame should be sent without waiting for
35				  an ACK even if it is a unicast frame
36   =============================  ========================================
37
38 * IEEE80211_RADIOTAP_RATE
39
40   legacy rate for the transmission (only for devices without own rate control)
41
42 * IEEE80211_RADIOTAP_MCS
43
44   HT rate for the transmission (only for devices without own rate control).
45   Also some flags are parsed
46
47   ============================  ========================
48   IEEE80211_RADIOTAP_MCS_SGI    use short guard interval
49   IEEE80211_RADIOTAP_MCS_BW_40  send in HT40 mode
50   ============================  ========================
51
52 * IEEE80211_RADIOTAP_DATA_RETRIES
53
54   number of retries when either IEEE80211_RADIOTAP_RATE or
55   IEEE80211_RADIOTAP_MCS was used
56
57 * IEEE80211_RADIOTAP_VHT
58
59   VHT mcs and number of streams used in the transmission (only for devices
60   without own rate control). Also other fields are parsed
61
62   flags field
63	IEEE80211_RADIOTAP_VHT_FLAG_SGI: use short guard interval
64
65   bandwidth field
66	* 1: send using 40MHz channel width
67	* 4: send using 80MHz channel width
68	* 11: send using 160MHz channel width
69
70The injection code can also skip all other currently defined radiotap fields
71facilitating replay of captured radiotap headers directly.
72
73Here is an example valid radiotap header defining some parameters::
74
75	0x00, 0x00, // <-- radiotap version
76	0x0b, 0x00, // <- radiotap header length
77	0x04, 0x0c, 0x00, 0x00, // <-- bitmap
78	0x6c, // <-- rate
79	0x0c, //<-- tx power
80	0x01 //<-- antenna
81
82The ieee80211 header follows immediately afterwards, looking for example like
83this::
84
85	0x08, 0x01, 0x00, 0x00,
86	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
87	0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
88	0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
89	0x10, 0x86
90
91Then lastly there is the payload.
92
93After composing the packet contents, it is sent by send()-ing it to a logical
94mac80211 interface that is in Monitor mode.  Libpcap can also be used,
95(which is easier than doing the work to bind the socket to the right
96interface), along the following lines:::
97
98	ppcap = pcap_open_live(szInterfaceName, 800, 1, 20, szErrbuf);
99	...
100	r = pcap_inject(ppcap, u8aSendBuffer, nLength);
101
102You can also find a link to a complete inject application here:
103
104https://wireless.wiki.kernel.org/en/users/Documentation/packetspammer
105
106Andy Green <andy@warmcat.com>
107