| 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 <[email protected]> |
