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Date:   Wed, 19 Jan 2022 10:45:33 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Jiasheng Jiang <jiasheng@iscas.ac.cn>
Cc:     dan.carpenter@oracle.com, arnd@arndb.de,
        gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] lkdtm/bugs: Check for the NULL pointer after calling
 kmalloc
Message-ID: <202201191044.69872866B@keescook>
References: <20220119122055.1826561-1-jiasheng@iscas.ac.cn>
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On Wed, Jan 19, 2022 at 08:20:55PM +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@iscas.ac.cn>
> ---
> Changelog
> 
> v1 -> v2
> 
> * Change 1. Add the kfree if fails.
> ---
>  drivers/misc/lkdtm/bugs.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
> index f4cb94a9aa9c..c35ea54824ac 100644
> --- a/drivers/misc/lkdtm/bugs.c
> +++ b/drivers/misc/lkdtm/bugs.c
> @@ -325,6 +325,11 @@ 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;
> +	}

This should explicitly yell about the memory failure. See the other
error cases for examples. I'd expect something like this before the
return:

		pr_err("FAIL: could not allocate required buffers\n");

-Kees

>  
>  	pr_info("Array access within bounds ...\n");
>  	/* For both, touch all bytes in the actual member size. */
> -- 
> 2.25.1
> 

-- 
Kees Cook