linux-kernel - Re: [PATCH 1/2] HID: logitech-hidpp: do not return the name length

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Date:	Wed, 10 Dec 2014 23:53:27 +0100
From:	Peter Wu <peter@...ensteyn.nl>
To:	Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Nestor Lopez Casado <nlopezcasad@...itech.com>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] HID: logitech-hidpp: do not return the name length

On Wednesday 10 December 2014 17:21:09 Benjamin Tissoires wrote:
> We do not make any use of the actual name length get through
> hidpp_get_device_name().
> 
> We can drop the extra code and simplify the API a bit.
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
>
> ---
>  drivers/hid/hid-logitech-hidpp.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
> index 1a6395d..3846305 100644
> --- a/drivers/hid/hid-logitech-hidpp.c
> +++ b/drivers/hid/hid-logitech-hidpp.c
> @@ -461,7 +461,7 @@ static int hidpp_devicenametype_get_device_name(struct hidpp_device *hidpp,
>  	return count;
>  }
>  
> -static char *hidpp_get_device_name(struct hidpp_device *hidpp, u8 *name_length)
> +static char *hidpp_get_device_name(struct hidpp_device *hidpp)
>  {
>  	u8 feature_type;
>  	u8 feature_index;
> @@ -484,7 +484,6 @@ static char *hidpp_get_device_name(struct hidpp_device *hidpp, u8 *name_length)
>  	if (!name)
>  		goto out_err;
>  
> -	*name_length = __name_length + 1;
>  	while (index < __name_length)
>  		index += hidpp_devicenametype_get_device_name(hidpp,
>  			feature_index, index, name + index,

hidpp_devicenametype_get_device_name can return a non-positive value if
the USB device is unplugged at the wrong time, or if a malicious device
is attached (and 0 is returned). An infinite loop is the result.

Can you apply this change in the patch or should I send you a separate
one?

	while (index < __name_length) {
		ret = hidpp_devicenametype_get_device_name(hidpp,
			feature_index, index, name + index,
			__name_length - index);
		if (ret <= 0) {
			kfree(name);
			return NULL;
		}
		index += ret;
	}

> @@ -493,7 +492,6 @@ static char *hidpp_get_device_name(struct hidpp_device *hidpp, u8 *name_length)
>  	return name;
>  
>  out_err:
> -	*name_length = 0;
>  	return NULL;

What about dropping the label out_err here and returning NULL in the
previous places?

>  }
>  
> @@ -989,7 +987,6 @@ static void hidpp_overwrite_name(struct hid_device *hdev, bool use_unifying)
>  {
>  	struct hidpp_device *hidpp = hid_get_drvdata(hdev);
>  	char *name;
> -	u8 name_length;
>  
>  	if (use_unifying)
>  		/*
> @@ -999,7 +996,7 @@ static void hidpp_overwrite_name(struct hid_device *hdev, bool use_unifying)
>  		 */
>  		name = hidpp_get_unifying_name(hidpp);
>  	else
> -		name = hidpp_get_device_name(hidpp, &name_length);
> +		name = hidpp_get_device_name(hidpp);
>  
>  	if (!name)
>  		hid_err(hdev, "unable to retrieve the name of the device");
> @@ -1053,7 +1050,6 @@ static void hidpp_connect_event(struct hidpp_device *hidpp)
>  	bool connected = atomic_read(&hidpp->connected);
>  	struct input_dev *input;
>  	char *name, *devm_name;
> -	u8 name_length;
>  
>  	if (hidpp->quirks & HIDPP_QUIRK_CLASS_WTP)
>  		wtp_connect(hdev, connected);
> @@ -1080,7 +1076,7 @@ static void hidpp_connect_event(struct hidpp_device *hidpp)
>  		return;
>  	}
>  
> -	name = hidpp_get_device_name(hidpp, &name_length);
> +	name = hidpp_get_device_name(hidpp);
>  	if (!name) {
>  		hid_err(hdev, "unable to retrieve the name of the device");
>  	} else {
> 

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