linux-kernel - Re: [PATCH 2/3] i2c: xlr: fix extra read/write at end of rx transfer

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-prev] [day] [month] [year] [list]

Date:	Tue, 15 Dec 2015 12:48:06 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] i2c: xlr: fix extra read/write at end of rx transfer

Wolfram Sang <wsa@...-dreams.de> writes:

> On Mon, Nov 02, 2015 at 02:03:37AM +0000, Mans Rullgard wrote:
>> The BYTECNT register holds the transfer size minus one.  Setting it
>> to the correct value requires a dummy read/write only for zero-length
>> transfers as it is impossible to request one from the hardware.  If a
>> zero-length transfer is requested, changing the length to 1 and setting
>> "buf" to a dummy location allows making the main loops less convoluted.
>> 
>> In other words, this patch makes the driver transfer the number of bytes
>> requested unless this is zero, which is not supported by the hardware,
>> in which case one byte is transferred instead.
>
> Uh, this is wrong, zero byte should really not transfer anything. We
> need to fix that and bail out, so probably something like
>
> 	if (!len)
> 		return -EOPNOTSUPP;

So the existing driver is wrong to allow it.  Makes sense to drop that.

> Also, the xlr_func() should mask out I2C_FUNC_SMBUS_QUICK.

OK.

> Other than that, the patch looks good to me.
>
> Out of curiosity, your first driver had the registers 32bit apart. Now
> you can deal with 8bit. Is this configurable on this SoC?

It's all 32 bits.  The XLR driver uses a u32 * to access the registers.

-- 
Måns Rullgård
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/