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- 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 many radiotap parameters being 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_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.
- * IEEE80211_RADIOTAP_TX_FLAGS
- IEEE80211_RADIOTAP_F_TX_NOACK: frame should be sent without waiting for
- an ACK even if it is a unicast frame
- * IEEE80211_RADIOTAP_RATE
- legacy rate for the transmission (only for devices without own rate control)
- * IEEE80211_RADIOTAP_MCS
- HT rate for the transmission (only for devices without own rate control).
- Also some flags are parsed
- IEEE80211_RADIOTAP_MCS_SGI: use short guard interval
- IEEE80211_RADIOTAP_MCS_BW_40: send in HT40 mode
- * IEEE80211_RADIOTAP_DATA_RETRIES
- number of retries when either IEEE80211_RADIOTAP_RATE or
- IEEE80211_RADIOTAP_MCS was used
- * IEEE80211_RADIOTAP_VHT
- VHT mcs and number of streams used in the transmission (only for devices
- without own rate control). Also other fields are parsed
- flags field
- IEEE80211_RADIOTAP_VHT_FLAG_SGI: use short guard interval
- bandwidth field
- 1: send using 40MHz channel width
- 4: send using 80MHz channel width
- 11: send using 160MHz channel width
- 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 some 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 a link to a complete inject application here:
- http://wireless.kernel.org/en/users/Documentation/packetspammer
- Andy Green <andy@warmcat.com>
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