linux-hardening - Re: [PATCH][next] block: scsi_ioctl: Avoid the use of one-element arrays

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Message-ID: <c06da705-3151-0902-066a-92d2e7c558bd@kernel.dk>
Date:   Fri, 2 Oct 2020 17:58:33 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH][next] block: scsi_ioctl: Avoid the use of one-element
 arrays

On 10/2/20 6:03 PM, Gustavo A. R. Silva wrote:
> On Fri, Oct 02, 2020 at 05:53:05PM -0600, Jens Axboe wrote:
>> On 10/2/20 5:10 PM, Gustavo A. R. Silva wrote:
>>> diff --git a/include/uapi/linux/cdrom.h b/include/uapi/linux/cdrom.h
>>> index 2817230148fd..6c34f6e2f1f7 100644
>>> --- a/include/uapi/linux/cdrom.h
>>> +++ b/include/uapi/linux/cdrom.h
>>> @@ -289,7 +289,10 @@ struct cdrom_generic_command
>>>  	unsigned char		data_direction;
>>>  	int			quiet;
>>>  	int			timeout;
>>> -	void			__user *reserved[1];	/* unused, actually */
>>> +	union {
>>> +		void		__user *reserved[1];	/* unused, actually */
>>> +		void            __user *unused;
>>> +	};
>>
>> What's the point of this union, why not just turn it into
>>
>> 	void *			__user *unused;
>>
>> ?
> 
> I just don't want to take any chances of breaking any user-space
> application that, for some reason, may be considering that field.

I guess that's a valid concern, who knows what applications are doing
to an ignored field.

I'll apply it, thanks.

-- 
Jens Axboe