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. The following information is parsed from the radiotap headers and used to control injection: * IEEE80211_RADIOTAP_RATE rate in 500kbps units, automatic if invalid or not present * IEEE80211_RADIOTAP_ANTENNA antenna to use, automatic if not present * IEEE80211_RADIOTAP_DBM_TX_POWER transmit power in dBm, automatic if not present * IEEE80211_RADIOTAP_FLAGS IEEE80211_RADIOTAP_F_FCS: FCS will be removed and recalculated IEEE80211_RADIOTAP_F_WEP: frame will be encrypted if key available IEEE80211_RADIOTAP_F_FRAG: frame will be fragmented if longer than the current fragmentation threshold. Note that this flag is only reliable when software fragmentation is enabled) The injection code can also skip all other currently defined radiotap fields facilitating replay of captured radiotap headers directly. 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>