linux-kernel - Re: hwmon: Error handling in w83793.c, w83791d.c, w83792d.c

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Date:   Wed, 11 Aug 2021 11:19:52 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Nadezda Lutovinova <lutovinova@...ras.ru>
Cc:     Marc Hulsman <m.hulsman@...elft.nl>,
        Jean Delvare <jdelvare@...e.com>,
        Rudolf Marek <r.marek@...embler.cz>,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org
Subject: Re: hwmon: Error handling in w83793.c, w83791d.c, w83792d.c

On Wed, Aug 11, 2021 at 10:52:03AM -0700, Guenter Roeck wrote:
> On Wed, Aug 11, 2021 at 07:15:14PM +0300, Nadezda Lutovinova wrote:
> > In w83793_detect_subclients(): if driver read tmp value sufficient for 
> > (tmp & 0x08) && (!(tmp & 0x80)) && ((tmp & 0x7) == ((tmp >> 4) & 0x7))
> > from device then Null pointer dereference occurs.
> > (It is possible if tmp = 0b0xyz1xyz, where same chars mean same numbers).
> > 
> > It can be fixed just by adding a checking for null pointer, patch for 
> > this is in the next letter. But a question arised:
> > The array w83793_data->lm75 is used once in this function after switching 
> > to devm_i2c_new_dummy_device() instead of i2c_new_dummy(). And this 
> > function is called once (from w83793_probe()). Maybe this array should be 
> > deleted from struct w83793_data?
> > 
> 
> That is part of it. However, the entire code is wrong. There is no need
> to check for I2C address overlap in the first place, and the i2c address
> for the second 'virtual' chip should start with 0x4c, not with 0x48.
> See w83793g/w83793ag datasheet, section 8.3.2.2.

Wait, that is wrong. Those are just the initial register values.
Forget the noise above; sorry for the confusion.

Guenter

> I assume the code was copied from w83791d and w83792d, where the addresses
> can indeed overlap.
> 
> Guenter
> 
> > The same situation in w83791d.c and in w83792d.
> > 
> > Found by Linux Driver Verification project (linuxtesting.org).
> > 
> > Signed-off-by: Nadezda Lutovinova <lutovinova@...ras.ru>