linux-kernel - Re: [PATCH 2/4] cdc-acm: fix possible invalid access when processing notification

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Date:   Wed, 15 Mar 2017 10:26:49 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Tobias Herzog <t-herzog@....de>
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH 2/4] cdc-acm: fix possible invalid access when
 processing notification

Am Dienstag, den 14.03.2017, 21:14 +0100 schrieb Tobias Herzog:
> Notifications may only be 8 bytes so long. Accessing the 9th and
> 10th byte of unimplemented/unknown notifications may be insecure.
> Also check the length of known notifications before accessing anything
> behind the 8th byte.
> 
> Signed-off-by: Tobias Herzog <t-herzog@....de>
> ---
>  drivers/usb/class/cdc-acm.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> index 40714fe..b99127e 100644
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -296,6 +296,12 @@ static void acm_process_notification(struct acm *acm, unsigned char *buf)
>  		break;
>  
>  	case USB_CDC_NOTIFY_SERIAL_STATE:
> +		if (dr->wLength != 2) {

Endianness

> +			dev_dbg(&acm->control->dev,
> +				"%s - malformed serial state\n", __func__);
> +			break;
> +		}
> +
>  		newctrl = get_unaligned_le16(data);
>  
>  		if (!acm->clocal && (acm->ctrlin & ~newctrl & ACM_CTRL_DCD)) {
> @@ -332,11 +338,10 @@ static void acm_process_notification(struct acm *acm, unsigned char *buf)
>  
>  	default:
>  		dev_dbg(&acm->control->dev,
> -			"%s - unknown notification %d received: index %d "
> -			"len %d data0 %d data1 %d\n",
> +			"%s - unknown notification %d received: index %d len %d\n",
>  			__func__,
>  			dr->bNotificationType, dr->wIndex,
> -			dr->wLength, data[0], data[1]);
> +			dr->wLength);
>  	}
>  }
>