linux-kernel - Re: [PATCH v4] lkdtm/bugs: Check for the NULL pointer after calling kmalloc

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Date:   Thu, 20 Jan 2022 10:14:08 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     gregkh@...uxfoundation.org, dan.carpenter@...cle.com,
        arnd@...db.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] lkdtm/bugs: Check for the NULL pointer after calling
 kmalloc

On Thu, Jan 20, 2022 at 05:29:36PM +0800, Jiasheng Jiang wrote:
> As the possible failure of the kmalloc(), the not_checked and checked
> could be NULL pointer.
> Therefore, it should be better to check it in order to avoid the
> dereference of the NULL pointer.
> Also, we need to kfree the 'not_checked' and 'checked' to avoid
> the memory leak if fails.
> And since it is just a test, it may directly return without error
> number.
> 
> Fixes: ae2e1aad3e48 ("drivers/misc/lkdtm/bugs.c: add arithmetic overflow and array bounds checks")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
> Changelog
> 
> v1 -> v2
> 
> * Change 1. Add the kfree if fails.
> 
> v2 -> v3
> 
> * Change 1. Add pr_err if fails.
> 
> v3 -> v4
> 
> * Change 1. Revert to v2 that remove the pr_err.
> ---
>  drivers/misc/lkdtm/bugs.c | 5 +++++
>  1 file changed, 5 insertions(+)

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

> 
> diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
> index 4282b625200f..072e3b742edf 100644
> --- a/drivers/misc/lkdtm/bugs.c
> +++ b/drivers/misc/lkdtm/bugs.c
> @@ -248,6 +248,11 @@ void lkdtm_ARRAY_BOUNDS(void)
>  
>  	not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL);
>  	checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL);
> +	if (!not_checked || !checked) {
> +		kfree(not_checked);
> +		kfree(checked);
> +		return;
> +	}
>  
>  	pr_info("Array access within bounds ...\n");
>  	/* For both, touch all bytes in the actual member size. */
> -- 
> 2.25.1
> 

-- 
Kees Cook