Packetspammer

Overview

A throughput-measurement tool using unencrypted broadcast packets. Adapted from Andy Green’s Packetspammer. Original git repository unavailable.

Note: the compiled binary only works on the AR9331 board, with OpenWRT 14

Note: latest code in ucsma-rate-control

Main functionalities

Construct a packet with a radiotap header and pass it to OS kernel by calling pcap_inject() in libpcap.
Set the delay between passing two packets to the OS kernel.
- Setting the delay to 0 tells the hardware to transmit as fast as possible.
Calculate the actual rate that it feeds packets to the OS kernel. This is done by using libpthread.

Getting started

Prerequisites

An AR9331 board running OpenWRT 14
The libpcap-dev package from apt
A mips-openwrt-linux-gcc binary, from compiling OpenWRT 14.
- Run build.sh from ucsma
Copying the packetspammer binary to the AR9331 (run make install; make send, or use scp)
A char device at /dev/ebbchar

Compiling

# Change PROJECT_ROOT if needed
PROJECT_ROOT="~/ucsma"
STAGING_DIR="$PROJECT_ROOT/staging_dir"
# Ensure STAGING_DIR exists
mkdir -p $STAGING_DIR
BUILD_DIR="$PROJECT_ROOT/build_dir"

# Prepare to compile packetspammer for the AR9331
cd "$PROJECT_ROOT"
cp -r "packetspammer" "build_dir"
CC="$BUILD_DIR/toolchain/OpenWrt-Toolchain-ar71xx-for-mips_34kc-gcc-4.8-linaro_uClibc-0.9.33.2/toolchain-mips_34kc_gcc-4.8-linaro_uClibc-0.9.33.2/bin/mips-openwrt-linux-gcc"

# Compile packetspammer
LPCAP="$PROJECT_ROOT/OpenWRT-14.07-JS9331/build_dir/target-mips_34kc_uClibc-0.9.33.2/libpcap-1.5.3/"
LPTHREAD="$PROJECT_ROOT/OpenWRT-14.07-JS9331/build_dir/toolchain-mips_34kc_gcc-4.8-linaro_uClibc-0.9.33.2/uClibc-0.9.33.2/lib/libpthread.so"
LIBS="-L$LPCAP -L$LPTHREAD"
cd "$BUILD_DIR/packetspammer"
$CC -Wall radiotap.c packetspammer.c -o packetspammer $LIBS -I/usr/include -lpcap -ldl -lpthread -std=gnu99

NOTE: STAGING_DIR is only defined to avoid this error:

mips-openwrt-linux-uclibc-gcc.bin: warning: environment variable 'STAGING_DIR' not defined

NOTE: -I/usr/include is used to fix gcc not finding pcap headers

Usage

./packetspammer -d <delay> <monitor_id>

delay: in μs, between packets to send
monitor_id: a string to specify the network device

About the code

ieee80211_radiotap.h: header for 80211 packet manipulation
radiotap.*: Unused
- NOTE: packetspammer should be using ieee80211_radiotap.h instead
packetspammer.h:
- NOTE: Typdefs for u8, u16 and u32 are made, but they could be using uint*_t
- NOTE: unlikely macro only used in radiotap.c, could be removed
- radiotap_hdr_t unused
  - NOTE: Flags are 1-bit wide, but are defined as uint8_t, a bitmap should just be defined
packetspammer.c:
- NOTE: PENUMBRA_RADIOTAP_DATA is unused
- Defines a template radiotap and 802.11 headers: u8aRadiotapHeader, u8aIeeeHeader
  - Note: for the radiotap header, a radiotap struct could have been used for intialization
- print_speed: thread routine that calculates and prints the sending rate every RATE_STAT_INTERVAL seconds
- Waits a variable amount of time between packet injections
  - Gets the free buffer space from /dev/ebbchar (in # packets? # bytes?)
  - Waits for as many μs as there is free buffer space
- Makes use of multiple pcap functions:
  - pcap_open_live for a handle to capture packets on a network device
  - pcap_datalink to determine the datalink-layer header type
    - Used to determine if the packet is Ethernet of Prism
  - pcap_compile to compile a string to a filter program
    - Used to capture either packets with an Ethernet header, or a Prism header
      - NOTE: this is probably outdated, Ethernet should be sufficient
  - pcap_setfilter to set the filter program compiled with pcap_compile, for a given device handle
  - pcap_freecode to free the pointer of the filter program compilted with pcap_compile
  - pcap_inject to inject a packet on a given network device
    - Sends the template Radiotap + Wifi header

Issues

gcc complains about flags from gcc < 4.4
make packetspammer cannot run on its own. (eg. it needs a location for the mips gcc)
make send depends on a hardcoded IP address, and relies on make install being run before (For documentation: no idea where /dev/ebbchar is being written into)

TODOs

Clean up radiotap.*
Clean up packetspammer.*: n80211HeaderLength, nCaptureHeaderLength, unlikely, u*, radiotap_hdr_t, …
Update / simplify build.sh
Fix Makefile
- Simplify install and send
- Parametrize packetspammer recipe