linux-kernel - Re: [PATCH] clk: npcm7xx: fix memory allocation

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Message-ID: <CAGXu5jK7VQSo=xsYVp5DPmUgULNt+wopyAXnK20z+LxZtyPfZA@mail.gmail.com>
Date:   Thu, 23 Aug 2018 16:17:59 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Avi Fishman <avifishman70@...il.com>,
        Tomer Maimon <tmaimon77@...il.com>,
        Patrick Venture <venture@...gle.com>,
        Nancy Yuen <yuenn@...gle.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, openbmc@...ts.ozlabs.org,
        linux-clk@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: npcm7xx: fix memory allocation

On Thu, Aug 23, 2018 at 4:06 PM, Gustavo A. R. Silva
<gustavo@...eddedor.com> wrote:
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
>
> struct foo {
>         int stuff;
>         void *entry[];
> };
>
> instance = kzalloc(sizeof(struct foo) + sizeof(void *) * count,
> GFP_KERNEL);
>
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
>
> instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);
>
> Notice that, currently, there is a bug during the allocation:
>
> sizeof(npcm7xx_clk_data) should be sizeof(*npcm7xx_clk_data)
>
> Fix this bug by using struct_size() in kzalloc()
>
> This issue was detected with the help of Coccinelle.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  drivers/clk/clk-npcm7xx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/clk-npcm7xx.c b/drivers/clk/clk-npcm7xx.c
> index 740af90..c5edf8f 100644
> --- a/drivers/clk/clk-npcm7xx.c
> +++ b/drivers/clk/clk-npcm7xx.c
> @@ -558,8 +558,8 @@ static void __init npcm7xx_clk_init(struct device_node *clk_np)
>         if (!clk_base)
>                 goto npcm7xx_init_error;
>
> -       npcm7xx_clk_data = kzalloc(sizeof(*npcm7xx_clk_data->hws) *
> -               NPCM7XX_NUM_CLOCKS + sizeof(npcm7xx_clk_data), GFP_KERNEL);
> +       npcm7xx_clk_data = kzalloc(struct_size(npcm7xx_clk_data, hws,
> +                                  NPCM7XX_NUM_CLOCKS), GFP_KERNEL);
>         if (!npcm7xx_clk_data)
>                 goto npcm7xx_init_np_err;
>
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security