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

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Message-ID: <20201003000338.GA13557@embeddedor>
Date:   Fri, 2 Oct 2020 19:03:38 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
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 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.

--
Gustavo