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diff --git a/Documentation/networking/mac80211-injection.rst b/Documentation/networking/mac80211-injection.rst new file mode 100644 index 000000000..63ba6611f --- /dev/null +++ b/Documentation/networking/mac80211-injection.rst @@ -0,0 +1,106 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================================= +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.rst. + +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: + +https://wireless.wiki.kernel.org/en/users/Documentation/packetspammer + +Andy Green <andy@warmcat.com> |