[ath9k-devel] Packet Injection in Monitor Mode Sending Packets Twice

[Mark Gannon <mark@truenorth.nu>]

I'm currently troubleshooting a problem using the ath9k driver where by 
packets injected via libpcap are sent twice with slightly different radiotap 
headers.  The issue happens with different software injecting the packets.

The system is an up to date Gentoo box where uname -a shows:
Linux scooby 3.18.5-gentoo #1 SMP PREEMPT Wed Feb 4 16:54:06 EST 2015 x86_64 
AMD A6-3650 APU with Radeon(tm) HD Graphics AuthenticAMD GNU/Linux

lspci shows the card as:
02:00.0 Network controller: Qualcomm Atheros AR93xx Wireless Network Adapter 
(rev 01)

In order to create the problem: 

1.  Load the driver:  modprobe ath9k debug=0x00000282
Note: The problem happens with or without the debug parameters 
2.  Create the monitor interface using: 
iw dev wlan0 interface add fish0 type monitor flags none
iw reg set US 
ifconfig fish0 up

3.  Download and build the packetspammer application from: 
https://wireless.wiki.kernel.org/en/users/Documentation/packetspammer
Note:  I edited Makefile to remove the -werror that was causing the make to 
fail.
4.  Start Wireshark listening to the fish0 interface.  
5.  Run packetspammer: ./packetspammer -d 1000000000000000000000000000 fish0
Note:  The long delay is to make the issue easier to see in the trace.

Result:
Wireshark shows two packets with slightly different lengths due to differences 
in the radiotap header.  The second packet has a much smaller radiotap header 
only setting the speed.  

In examining the driver code in the kernel tree, there appears to be a 
difference between main.c and htc_drv_main.c with regard to packet injection.  
The latter includes a section with the comment: "Associate a station with the 
interface for packet injection."  After the comment, is code to associate a 
station with the interface.  As near as I can tell, this process doesn't occur 
in main.c, which is the code being executed for my NIC.  Could this be the 
reason for the duplicate packets?

Any help addressing this issue is greatly appreciated.

Regards,

Mark Gannon

-- 
You have to accept whatever comes, and the only important thing is that you 
meet it with the best you have to give. 

	? Eleanor Roosevelt
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