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1.. SPDX-License-Identifier: GPL-2.02 3=========================================4How to use packet injection with mac802115=========================================6 7mac80211 now allows arbitrary packets to be injected down any Monitor Mode8interface from userland. The packet you inject needs to be composed in the9following format::10 11 [ radiotap header ]12 [ ieee80211 header ]13 [ payload ]14 15The radiotap format is discussed in16./Documentation/networking/radiotap-headers.rst.17 18Despite many radiotap parameters being currently defined, most only make sense19to appear on received packets. The following information is parsed from the20radiotap headers and used to control injection:21 22 * IEEE80211_RADIOTAP_FLAGS23 24 ========================= ===========================================25 IEEE80211_RADIOTAP_F_FCS FCS will be removed and recalculated26 IEEE80211_RADIOTAP_F_WEP frame will be encrypted if key available27 IEEE80211_RADIOTAP_F_FRAG frame will be fragmented if longer than the28 current fragmentation threshold.29 ========================= ===========================================30 31 * IEEE80211_RADIOTAP_TX_FLAGS32 33 ============================= ========================================34 IEEE80211_RADIOTAP_F_TX_NOACK frame should be sent without waiting for35 an ACK even if it is a unicast frame36 ============================= ========================================37 38 * IEEE80211_RADIOTAP_RATE39 40 legacy rate for the transmission (only for devices without own rate control)41 42 * IEEE80211_RADIOTAP_MCS43 44 HT rate for the transmission (only for devices without own rate control).45 Also some flags are parsed46 47 ============================ ========================48 IEEE80211_RADIOTAP_MCS_SGI use short guard interval49 IEEE80211_RADIOTAP_MCS_BW_40 send in HT40 mode50 ============================ ========================51 52 * IEEE80211_RADIOTAP_DATA_RETRIES53 54 number of retries when either IEEE80211_RADIOTAP_RATE or55 IEEE80211_RADIOTAP_MCS was used56 57 * IEEE80211_RADIOTAP_VHT58 59 VHT mcs and number of streams used in the transmission (only for devices60 without own rate control). Also other fields are parsed61 62 flags field63 IEEE80211_RADIOTAP_VHT_FLAG_SGI: use short guard interval64 65 bandwidth field66 * 1: send using 40MHz channel width67 * 4: send using 80MHz channel width68 * 11: send using 160MHz channel width69 70The injection code can also skip all other currently defined radiotap fields71facilitating replay of captured radiotap headers directly.72 73Here is an example valid radiotap header defining some parameters::74 75 0x00, 0x00, // <-- radiotap version76 0x0b, 0x00, // <- radiotap header length77 0x04, 0x0c, 0x00, 0x00, // <-- bitmap78 0x6c, // <-- rate79 0x0c, //<-- tx power80 0x01 //<-- antenna81 82The ieee80211 header follows immediately afterwards, looking for example like83this::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, 0x8690 91Then lastly there is the payload.92 93After composing the packet contents, it is sent by send()-ing it to a logical94mac80211 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 right96interface), 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/packetspammer105 106Andy Green <andy@warmcat.com>107