linux-kernel - Re: [PATCH] media: v4l2-core: only zero-out ioctl-read buffers

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Message-ID: <20200108101004.GC4383@kekkonen.localdomain>
Date:   Wed, 8 Jan 2020 12:10:04 +0200
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        syzbot+54fd8cca4b7226c94b8e@...kaller.appspotmail.com,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Vandana BN <bnvandana@...il.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: v4l2-core: only zero-out ioctl-read buffers

On Wed, Jan 08, 2020 at 11:00:00AM +0100, Arnd Bergmann wrote:
> The memset() got moved out of the check for _IOC_NONE, so passing a
> made-up command number with a size but no direction would allow clearing
> data on user-provided pointers.
> 
> Move video_get_user() back into the _IOC_NONE check where it belongs.
> 
> Reported-by: syzbot+54fd8cca4b7226c94b8e@...kaller.appspotmail.com
> Fixes: 6c625c01c7a6 ("media: v4l2-core: split out data copy from video_usercopy")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for the fix, Arnd!

Reviewed-by: Sakari Ailus <sakari.ailus@...ux.intel.com>

> ---
>  drivers/media/v4l2-core/v4l2-ioctl.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index b0d670715c27..0f11fc6b5447 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -3208,12 +3208,12 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
>  			parg = mbuf;
>  		}
>  
> +		err = video_get_user((void __user *)arg, parg, orig_cmd,
> +				     &always_copy);
> +		if (err)
> +			goto out;
>  	}
>  
> -	err = video_get_user((void __user *)arg, parg, orig_cmd, &always_copy);
> -	if (err)
> -		goto out;
> -
>  	err = check_array_args(cmd, parg, &array_size, &user_ptr, &kernel_ptr);
>  	if (err < 0)
>  		goto out;

-- 
Sakari Ailus
sakari.ailus@...ux.intel.com