ACK/Cmnt: [PATCH] Input: ims-psu - check if CDC union descriptor is sane

[Stefan Bader]

On 20.07.2018 17:38, Colin King wrote:
> From: Dmitry Torokhov <dmitry.torokhov at gmail.com>
> 
> CVE-2017-16645
> 
> Before trying to use CDC union descriptor, try to validate whether that it
> is sane by checking that intf->altsetting->extra is big enough and that
> descriptor bLength is not too big and not too small.
> 
> Reported-by: Andrey Konovalov <andreyknvl at google.com>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov at gmail.com>
> (clean cherry pick from upstream commit ea04efee7635c9120d015dcdeeeb6988130cb67a)
> Signed-off-by: Colin Ian King <colin.king at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---

-> (cherry picked from commit ea04efee7635c9120d015dcdeeeb6988130cb67a)

>  drivers/input/misc/ims-pcu.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/misc/ims-pcu.c b/drivers/input/misc/ims-pcu.c
> index 6bf82ea..ae47312 100644
> --- a/drivers/input/misc/ims-pcu.c
> +++ b/drivers/input/misc/ims-pcu.c
> @@ -1635,13 +1635,25 @@ static void ims_pcu_buffers_free(struct ims_pcu *pcu)
>  		return NULL;
>  	}
>  
> -	while (buflen > 0) {
> +	while (buflen >= sizeof(*union_desc)) {
>  		union_desc = (struct usb_cdc_union_desc *)buf;
>  
> +		if (union_desc->bLength > buflen) {
> +			dev_err(&intf->dev, "Too large descriptor\n");
> +			return NULL;
> +		}
> +
>  		if (union_desc->bDescriptorType == USB_DT_CS_INTERFACE &&
>  		    union_desc->bDescriptorSubType == USB_CDC_UNION_TYPE) {
>  			dev_dbg(&intf->dev, "Found union header\n");
> -			return union_desc;
> +
> +			if (union_desc->bLength >= sizeof(*union_desc))
> +				return union_desc;
> +
> +			dev_err(&intf->dev,
> +				"Union descriptor to short (%d vs %zd\n)",
> +				union_desc->bLength, sizeof(*union_desc));
> +			return NULL;
>  		}
>  
>  		buflen -= union_desc->bLength;
> 


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