linux-kernel - Re: [PATCH v4 06/21] hwmon: (mr75203) fix multi-channel voltage reading

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Date:   Tue, 6 Sep 2022 17:10:50 +0300
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Eliav Farber <farbere@...zon.com>
Cc:     jdelvare@...e.com, linux@...ck-us.net, robh+dt@...nel.org,
        p.zabel@...gutronix.de, rtanwar@...linear.com,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, hhhawa@...zon.com, jonnyc@...zon.com
Subject: Re: [PATCH v4 06/21] hwmon: (mr75203) fix multi-channel voltage
 reading

On Tue, Sep 06, 2022 at 08:33:41AM +0000, Eliav Farber wrote:
> Fix voltage allocation and reading to support all channels in all VMs.
> Prior to this change allocation and reading were done only for the first
> channel in each VM.
> This change counts the total number of channels for allocation, and takes
> into account the channel offset when reading the sample data register.

...

> +		total_ch = ch_num * vm_num;
> +		in_config = devm_kcalloc(dev, total_ch + 1,
>  					 sizeof(*in_config), GFP_KERNEL);

Strictly speaking this should be `size_add(size_mul(...) ...)` construction
from overflow.h.

		total_ch = size_mul(ch_num, vm_num);
		in_config = devm_kcalloc(dev, size_add(total_ch, 1),
					 sizeof(*in_config), GFP_KERNEL);

Alternatively before doing all these, add a check

		if (array3_size(ch_num, vm_num, sizeof(*in_config)) < SIZE_MAX - sizeof(*in_config))
			return -EOVERFLOW;

But this is a bit monstrous. Seems like the above looks and feels better.

Also for backporting purposes perhaps it's fine to do without using those macro
helpers.

>  		if (!in_config)
>  			return -ENOMEM;


-- 
With Best Regards,
Andy Shevchenko