linux-kernel - Re: [PATCH] nullb: Adjust device size calculation in null_alloc

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Message-ID: <c50f7ca2-8f3d-4b7e-bd50-1957e4a09b7b@kernel.org>
Date: Tue, 17 Sep 2024 09:21:05 +0200
From: Damien Le Moal <dlemoal@...nel.org>
To: Aleksandr Mishin <amishin@...rgos.ru>, Shaohua Li <shli@...com>
Cc: Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>,
 Johannes Thumshirn <johannes.thumshirn@....com>,
 Chaitanya Kulkarni <kch@...dia.com>, Zhu Yanjun <yanjun.zhu@...ux.dev>,
 Chengming Zhou <zhouchengming@...edance.com>,
 John Garry <john.g.garry@...cle.com>, Yu Kuai <yukuai3@...wei.com>,
 Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 lvc-project@...uxtesting.org
Subject: Re: [PATCH] nullb: Adjust device size calculation in null_alloc_dev()

On 2024/09/17 16:07, Aleksandr Mishin wrote:
> In null_alloc_dev() device size is a subject to overflow because 'g_gb'
> (which is module parameter, may have any value and is not validated
> anywhere) is not cast to a larger data type before performing arithmetic.
> 
> Cast 'g_gb' to unsigned long to prevent overflow.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 2984c8684f96 ("nullb: factor disk parameters")
> Signed-off-by: Aleksandr Mishin <amishin@...rgos.ru>
> ---
>  drivers/block/null_blk/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index 2f0431e42c49..5edbf9c0aceb 100644
> --- a/drivers/block/null_blk/main.c
> +++ b/drivers/block/null_blk/main.c
> @@ -762,7 +762,7 @@ static struct nullb_device *null_alloc_dev(void)
>  		return NULL;
>  	}
>  
> -	dev->size = g_gb * 1024;
> +	dev->size = (unsigned long)g_gb * 1024;

This still does not prevent overflows... So what about doing a proper check ?

>  	dev->completion_nsec = g_completion_nsec;
>  	dev->submit_queues = g_submit_queues;
>  	dev->prev_submit_queues = g_submit_queues;

-- 
Damien Le Moal
Western Digital Research