linux-kernel - Re: [rt2x00-users] [PATCH RFC] rt2500usb: disable broken HW encryption by default

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Message-ID: <a32f33a41003230815v1870a371oef9392806b5b2248@mail.gmail.com>
Date:	Tue, 23 Mar 2010 16:15:12 +0100
From:	Ivo Van Doorn <ivdoorn@...il.com>
To:	Ondrej Zary <linux@...nbow-software.org>
Cc:	rt2x00 Users List <users@...x00.serialmonkey.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [rt2x00-users] [PATCH RFC] rt2500usb: disable broken HW 
	encryption by default

On Tue, Mar 23, 2010 at 4:09 PM, Ondrej Zary <linux@...nbow-software.org> wrote:
> On Tuesday 23 March 2010, Ivo Van Doorn wrote:
>> On Tue, Mar 23, 2010 at 10:27 AM, Ondrej Zary
>>
>> <linux@...nbow-software.org> wrote:
>> > On Monday 22 March 2010, Ivo Van Doorn wrote:
>> >> >> But I though it was mentioned that disabling HW crypto didn't solve
>> >> >> the issue due to a second bug in a later kernel?
>> >> >
>> >> > That was a false positive. Probably because the device was not
>> >> > unplugged between the tests (and looks like the driver does not
>> >> > initialize the chip completely). It's not reliable, it sometimes stops
>> >> > working after reboot.
>> >>
>> >> Ah well that at least simplifies the problem. I'll have to retest
>> >> rt2500usb soon to see why the HW crypto failed. I am sure I had it
>> >> working for WEP, WPA and WPA2
>> >> before I submitted the patch.
>> >
>> > So let's try to fix it instead of disabling.
>> >
>> > First, the unrealiability (keeping HW encryption disabled). With the
>> > driver loaded but not doing anything more, the register dumps are same
>> > for both working and non-working case (dump-init.txt).
>> >
>> > dump-good-connected.txt is a dump after successful association and DHCP
>> > dump-bad-attempt.txt is a dump after successful association during
>> > non-working DHCP attempt
>> > dump-bad-after.txt is a dump after DHCP timed out
>>
>> With association working, but DHCP failing it most likely means that
>> somehow the frame was malformatted.
>> The code for HW crypto alters the frame (alters IV/EIV/ICV data etc).
>> And that is commonly the source of
>> problems, because what has to be done depends heavily on the encryption
>> type.
>>
>> So could you verify which of the encryption types (WEP,WPA,WPA2) is
>> failing or working? That would give a starting
>> position on which bytes might be corrupted.
>
> I was testing only with WPA2 before. I did some more testing today. The results:
>
> No encryption - works always
> WEP - sometimes works, sometimes not - same with and without HW encryption
> WPA - sometimes works, sometimes not - same with and without HW encryption
> WPA2 - never works with HW encryption
>     - sometimes works, sometimes not without HW encryptionn
>
> So it seems that there are two problems:
>  1. random problems with any encryption
>  2. WPA2 is broken with HW encryption
>
> When the "random" problem appears, this appears in dmesg:
> wlan1: authenticate with 00:13:d4:0f:f3:17 (try 1)
> wlan1: authenticated
> wlan1: associate with 00:13:d4:0f:f3:17 (try 1)
> wlan1: RX AssocResp from 00:13:d4:0f:f3:17 (capab=0x411 status=0 aid=2)
> wlan1: associated
> phy0 -> rt2500usb_set_device_state: Error - Device failed to enter state 3 (-16).
> phy0 -> rt2500usb_set_device_state: Error - Device failed to enter state 3 (-16).
> No probe response from AP 00:13:d4:0f:f3:17 after 500ms, disconnecting.
>
> Disabling call to rt2500usb_set_state() in rt2500usb_set_device_state() seems
> to fix problem 1. After this change, WEP and WPA work always regardless of
> HW encryption (and WPA2 works always without it).

Ok, lets focus on the HW crypto for now.

If WPA2 fails, then the WPA2 specific code for IV/EIV/ICV isn't
working. Most likely
the device either doesn't send all data back to the driver (while the
driver does expect it)
or it adds additional data which the driver doesn't expect. (See
rt2x00crypto.c for the frame
manipulation during HW crypto).

Could you check the full packet data of a DHCP request with and
without HW crypto?
That might give a clue about what the hardware is sending for extra data.

Ivo
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