linux-kernel - Re: [PATCH] memstick: jmb38x_ms: Prefer struct

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Date:   Tue, 14 Sep 2021 13:23:55 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Len Baker <len.baker@....com>
Cc:     Maxim Levitsky <maximlevitsky@...il.com>,
        Alex Dubov <oakad@...oo.com>,
        Kees Cook <keescook@...omium.org>, Tom Rix <trix@...hat.com>,
        linux-hardening@...r.kernel.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memstick: jmb38x_ms: Prefer struct_size over open coded arithmetic

On Sat, 11 Sept 2021 at 15:22, 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 struct_size() helper to do the arithmetic instead of the
> argument "size + count * size" 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>

Applied for next, thanks!

Kind regards
Uffe


> ---
>  drivers/memstick/host/jmb38x_ms.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/memstick/host/jmb38x_ms.c b/drivers/memstick/host/jmb38x_ms.c
> index f9a93b0565e1..a7a0f0caea15 100644
> --- a/drivers/memstick/host/jmb38x_ms.c
> +++ b/drivers/memstick/host/jmb38x_ms.c
> @@ -927,8 +927,7 @@ static int jmb38x_ms_probe(struct pci_dev *pdev,
>                 goto err_out_int;
>         }
>
> -       jm = kzalloc(sizeof(struct jmb38x_ms)
> -                    + cnt * sizeof(struct memstick_host *), GFP_KERNEL);
> +       jm = kzalloc(struct_size(jm, hosts, cnt), GFP_KERNEL);
>         if (!jm) {
>                 rc = -ENOMEM;
>                 goto err_out_int;
> --
> 2.25.1
>