linux-kernel - Re: [PATCH v4] hwmon: (acpi_power_meter) replace open-coded kmemdup

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Message-ID: <202309251101.1544F5F@keescook>
Date:   Mon, 25 Sep 2023 11:02:05 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4] hwmon: (acpi_power_meter) replace open-coded
 kmemdup_nul

On Mon, Sep 25, 2023 at 03:43:23AM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> Let's refactor this kcalloc() + strncpy() into a kmemdup_nul() which has
> more obvious behavior and is less error prone.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Changes in v4:
> - drop +1 from length arg (thanks Kees)
> - reword subject line (thanks Kees)
> - rebase onto 6465e260f4879080
> - Link to v3: https://lore.kernel.org/r/20230921-strncpy-drivers-hwmon-acpi_power_meter-c-v3-1-307552c6ec3f@google.com
> 
> Changes in v3:
> - refactor to use kmemdup_nul() (thanks Thomas and Kees)
> - change commit msg to reflect ^
> - rebase onto 2cf0f71562387282
> - Link to v2: https://lore.kernel.org/r/20230919-strncpy-drivers-hwmon-acpi_power_meter-c-v2-1-8348432d6442@google.com
> 
> Changes in v2:
> - use memcpy over strscpy (thanks Kees)
> - Link to v1: https://lore.kernel.org/r/20230914-strncpy-drivers-hwmon-acpi_power_meter-c-v1-1-905297479fe8@google.com
> ---
>  drivers/hwmon/acpi_power_meter.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwmon/acpi_power_meter.c b/drivers/hwmon/acpi_power_meter.c
> index fa28d447f0df..c13b5c8a0433 100644
> --- a/drivers/hwmon/acpi_power_meter.c
> +++ b/drivers/hwmon/acpi_power_meter.c
> @@ -796,14 +796,13 @@ static int read_capabilities(struct acpi_power_meter_resource *resource)
>  			goto error;
>  		}
>  
> -		*str = kcalloc(element->string.length + 1, sizeof(u8),
> -			       GFP_KERNEL);
> +		*str = kmemdup_nul(element->string.pointer, element->string.length,
> +						 GFP_KERNEL);

This whitespace looks weird -- I'd expect this to line up with
"element", like this:

> +		*str = kmemdup_nul(element->string.pointer, element->string.length,
> +				   GFP_KERNEL);

Otherwise, yes, looks correct.

-- 
Kees Cook