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1 | How to use packet injection with mac80211 |
2 | ========================================= |
3 | |
4 | mac80211 now allows arbitrary packets to be injected down any Monitor Mode |
5 | interface from userland. The packet you inject needs to be composed in the |
6 | following format: |
7 | |
8 | [ radiotap header ] |
9 | [ ieee80211 header ] |
10 | [ payload ] |
11 | |
12 | The radiotap format is discussed in |
13 | ./Documentation/networking/radiotap-headers.txt. |
14 | |
15 | Despite many radiotap parameters being currently defined, most only make sense |
16 | to appear on received packets. The following information is parsed from the |
17 | radiotap 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 | |
27 | The injection code can also skip all other currently defined radiotap fields |
28 | facilitating replay of captured radiotap headers directly. |
29 | |
30 | Here is an example valid radiotap header defining some parameters |
31 | |
32 | 0x00, 0x00, // <-- radiotap version |
33 | 0x0b, 0x00, // <- radiotap header length |
34 | 0x04, 0x0c, 0x00, 0x00, // <-- bitmap |
35 | 0x6c, // <-- rate |
36 | 0x0c, //<-- tx power |
37 | 0x01 //<-- antenna |
38 | |
39 | The ieee80211 header follows immediately afterwards, looking for example like |
40 | this: |
41 | |
42 | 0x08, 0x01, 0x00, 0x00, |
43 | 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, |
44 | 0x13, 0x22, 0x33, 0x44, 0x55, 0x66, |
45 | 0x13, 0x22, 0x33, 0x44, 0x55, 0x66, |
46 | 0x10, 0x86 |
47 | |
48 | Then lastly there is the payload. |
49 | |
50 | After composing the packet contents, it is sent by send()-ing it to a logical |
51 | mac80211 interface that is in Monitor mode. Libpcap can also be used, |
52 | (which is easier than doing the work to bind the socket to the right |
53 | interface), along the following lines: |
54 | |
55 | ppcap = pcap_open_live(szInterfaceName, 800, 1, 20, szErrbuf); |
56 | ... |
57 | r = pcap_inject(ppcap, u8aSendBuffer, nLength); |
58 | |
59 | You can also find a link to a complete inject application here: |
60 | |
61 | http://wireless.kernel.org/en/users/Documentation/packetspammer |
62 | |
63 | Andy Green <andy@warmcat.com> |
64 |
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