linux-hardening - Re: [PATCH] cpufreq: powernow: Prefer kcalloc over open coded arithmetic

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Date:   Mon, 6 Sep 2021 19:05:06 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Len Baker <len.baker@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        linux-hardening@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: powernow: Prefer kcalloc over open coded arithmetic

On Sat, Sep 4, 2021 at 5:16 PM Len Baker <len.baker@....com> wrote:
>
> As noted in the "Deprecated Interfaces, Language Features, Attributes,
> and Conventions" documentation [1], size calculations (especially
> multiplication) should not be performed in memory allocator (or similar)
> function arguments due to the risk of them overflowing. This could lead
> to values wrapping around and a smaller allocation being made than the
> caller was expecting. Using those allocations could lead to linear
> overflows of heap memory and other misbehaviors.
>
> So, use the purpose specific kcalloc() function instead of the argument
> size * count in the kzalloc() function.
>
> [1] https://www.kernel.org/doc/html/v5.14/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
>
> Signed-off-by: Len Baker <len.baker@....com>

I'm assuming that this patch will be picked up by the powerpc arch maintainers.

> ---
>  drivers/cpufreq/powernow-k7.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/powernow-k7.c b/drivers/cpufreq/powernow-k7.c
> index 5d515fc34836..a9d2c7bae235 100644
> --- a/drivers/cpufreq/powernow-k7.c
> +++ b/drivers/cpufreq/powernow-k7.c
> @@ -174,8 +174,8 @@ static int get_ranges(unsigned char *pst)
>         unsigned int speed;
>         u8 fid, vid;
>
> -       powernow_table = kzalloc((sizeof(*powernow_table) *
> -                               (number_scales + 1)), GFP_KERNEL);
> +       powernow_table = kcalloc(number_scales + 1, sizeof(*powernow_table),
> +                                GFP_KERNEL);
>         if (!powernow_table)
>                 return -ENOMEM;
>
> --
> 2.25.1
>