Mesh on Insignificant Bits

Encrypted mesh PSA

Mon, 31 Oct 2016 13:32:19 +0000

I’m a bit late writing this up, as lately wifi stuff has taken a back seat to the day job. But, I’ve now seen the following issue reported more than once, so hopefully this post will save the other two mesh users some grief.

If you are running an encrypted mesh on wpa_supplicant or (ye gods) authsae, take note:

Encrypted mesh on kernel 4.8 will not interoperate with kernel < 4.8
wpa_supplicant 2.6 will not interoperate with 2.5
authsae as of commit 706a2cf will not interoperate with that of commit 813ec0e [1]
wpa_supplicant 2.6 and authsae commit 706a2cf require additional configuration to work with kernel < 4.8 (see below).

memory Âµ-optimizing

Tue, 15 Mar 2016 12:27:35 +0000

While looking at some kmalloc statistics for my little corner of wireless, I found a new tool for the toolbox: perf kmem. To test it out, I ran a simulated connected 25-node mesh in mac80211_hwsim.

Here’s what perf kmem stat --caller had to say:

---------------------------------------------------------------------
 Callsite            | Total_alloc/Per | Total_req/Per  | Hit   | ...
---------------------------------------------------------------------
 mesh_table_alloc+3e |      1600/32    |       400/8    |    50 |
 mesh_rmc_init+23    |    204800/8192  |    102600/4104 |    25 |
 mesh_path_new.const |    315904/512   |    241864/392  |   617 |
[...]

The number of mesh nodes shows up in the ‘Hit’ column in various ways: we can pretty easily see that mesh_table_alloc is called twice per mesh device, mesh_rmc_init is called once, and mesh_path_new is called at least once for every peer (617 ~= 25 * 24). We might scan the hit column to see if there are any cases in our code that perform unexpectedly high numbers of allocations, signifying a bug or poor design.

sae.py

Thu, 31 Dec 2015 23:57:47 +0000

For a while now, I’ve wanted an easy way to decrypt a mesh packet capture when I know the SAE passphrase. This would be quite handy for debugging.

I reasoned that, if I knew the shared secret, and had captured the over-the-air exchange, it should be possible to make such a tool, right? We know everything each station knows in that case, don’t we?

So I spent a bit of time last week reimplementing SAE in python to come to grips with its various steps. And I found my reasoning was flawed.

VHT mesh

Tue, 14 Jul 2015 04:43:30 +0000

…is a thing now.

# iw dev
phy#0
    Interface wlan0
		ifindex 4
		wdev 0x1
		addr 30:b5:c2:fb:34:d8
		type mesh point
		channel 149 (5745 MHz), width: 80 MHz, center1: 5775 MHz

# iperf -c 192.168.1.20
------------------------------------------------------------
Client connecting to 192.168.1.20, TCP port 5001
TCP window size: 43.8 KByte (default)
------------------------------------------------------------
[  3] local 192.168.1.21 port 34175 connected with 192.168.1.20 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   148 MBytes   124 Mbits/sec

mesh on ath10k

Tue, 28 Apr 2015 18:25:16 +0000

I’ve had my ath10k AP (TP-Link Archer C7 v2) since last October or so, with the goal of having a VHT-capable device with which to test (currently non-existent) VHT mesh. Unfortunately, for nearly all of that time, I’ve been stuck on a firmware crash shortly after bringing up the device. Not that I’ve spent a whole lot of time on it, but there’s only so much one can do when getting to the point of “firmware crashes and it has something to do with peers but that’s all I know and I don’t have the time, tools, or code to dig deeper.”