linux-kernel - rf69_set_deviation in rf69.c (pi433 driver)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180605031120.GB1981@hle-laptop.local>
Date:   Mon, 4 Jun 2018 23:11:20 -0400
From:   Hugo Lefeuvre <hle@....eu.com>
To:     Marcus Wolf <linux@...f-entwicklungen.de>
Cc:     Valentin Vidic <Valentin.Vidic@...Net.hr>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>, hle@....eu.com
Subject: rf69_set_deviation in rf69.c (pi433 driver)

Hi Marcus,

I have been taking a look at the pi433 driver these last days, and started
working on the remaining TODOs. I just stumbled across the following
one (drivers/staging/pi433/rf69.c):

245         // TODO: Dependency to bitrate
246         if (deviation < 600 || deviation > 500000) {
247                 dev_dbg(&spi->dev, "set_deviation: illegal input param");
248                 return -EINVAL;
249         }

According to the datasheet[0], the deviation should always be smaller
than 300kHz, and the following equation should be respected:

  (1) FDA + BRF/2 =< 500 kHz

Why did you choose 500kHz as max for FDA, instead of 300kHz ? It looks like
a bug to me.

Concerning the TODO, I can see two solutions currently:

1. Introduce a new rf69_get_bit_rate function which reads REG_BITRATE_MSB
   and REG_BITRATE_LSB and returns reconstructed BRF.
   We could use this function in rf69_set_deviation to retrieve the BRF.

+ clean
+ intuitive
- heavy / slow

2. Store BRF somewhere in rf69.c, initialize it with the default value
   (4.8 kb/s) and update it when rf69_set_bit_rate is called.

+ easy
- dirty, doesn't fit well with the design of rf69.c (do not store
  anything, simply expose API)

I'd really prefer going for the first one, but I wanted to have your opinion
on this.

Thanks for your work !

Best regards,
 Hugo

[0] http://www.hoperf.com/upload/rf/RFM69CW-V1.1.pdf

[CC-ing Valentin Vidic, he was quite active on the pi433 driver these
last months]

-- 
             Hugo Lefeuvre (hle)    |    www.owl.eu.com
4096/ 9C4F C8BF A4B0 8FC5 48EB 56B8 1962 765B B9A8 BACA

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)