2007-07-11 01:29:37 +08:00
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How to use packet injection with mac80211
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=========================================
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mac80211 now allows arbitrary packets to be injected down any Monitor Mode
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interface from userland. The packet you inject needs to be composed in the
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following format:
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[ radiotap header ]
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[ ieee80211 header ]
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[ payload ]
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The radiotap format is discussed in
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./Documentation/networking/radiotap-headers.txt.
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Despite 13 radiotap argument types are currently defined, most only make sense
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2007-09-26 23:53:18 +08:00
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to appear on received packets. The following information is parsed from the
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radiotap headers and used to control injection:
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2007-07-11 01:29:37 +08:00
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2007-09-26 23:53:18 +08:00
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* IEEE80211_RADIOTAP_RATE
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2007-07-11 01:29:37 +08:00
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2007-09-26 23:53:18 +08:00
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rate in 500kbps units, automatic if invalid or not present
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2007-07-11 01:29:37 +08:00
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2007-09-26 23:53:18 +08:00
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* IEEE80211_RADIOTAP_ANTENNA
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antenna to use, automatic if not present
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* IEEE80211_RADIOTAP_DBM_TX_POWER
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transmit power in dBm, automatic if not present
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* IEEE80211_RADIOTAP_FLAGS
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IEEE80211_RADIOTAP_F_FCS: FCS will be removed and recalculated
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IEEE80211_RADIOTAP_F_WEP: frame will be encrypted if key available
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IEEE80211_RADIOTAP_F_FRAG: frame will be fragmented if longer than the
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current fragmentation threshold. Note that
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this flag is only reliable when software
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fragmentation is enabled)
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The injection code can also skip all other currently defined radiotap fields
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facilitating replay of captured radiotap headers directly.
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2007-07-11 01:29:37 +08:00
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Here is an example valid radiotap header defining these three parameters
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0x00, 0x00, // <-- radiotap version
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0x0b, 0x00, // <- radiotap header length
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0x04, 0x0c, 0x00, 0x00, // <-- bitmap
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0x6c, // <-- rate
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0x0c, //<-- tx power
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0x01 //<-- antenna
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The ieee80211 header follows immediately afterwards, looking for example like
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this:
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0x08, 0x01, 0x00, 0x00,
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
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0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
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0x10, 0x86
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Then lastly there is the payload.
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After composing the packet contents, it is sent by send()-ing it to a logical
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mac80211 interface that is in Monitor mode. Libpcap can also be used,
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(which is easier than doing the work to bind the socket to the right
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interface), along the following lines:
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ppcap = pcap_open_live(szInterfaceName, 800, 1, 20, szErrbuf);
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...
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r = pcap_inject(ppcap, u8aSendBuffer, nLength);
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You can also find sources for a complete inject test applet here:
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http://penumbra.warmcat.com/_twk/tiki-index.php?page=packetspammer
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Andy Green <andy@warmcat.com>
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