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

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Date:	Thu, 11 Dec 2014 01:06:17 +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 18:01:52 Benjamin Tissoires wrote:
> On Dec 10 2014 or thereabouts, Peter Wu wrote:
> > 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.
> 
> Oh, yes, you are definitively right.
> 
> > 
> > Can you apply this change in the patch or should I send you a separate
> > one?
> 
> Feel free to send your patch directly to the list.
> 
> > 
> > 	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?
> 
> Yep, good idea. You can either send a patch for that if you want to take
> credits, or I can send a v2. It's up to you.
> 
> Cheers,
> Benjamin

I found another place where a boundary check is missing, but will treat
that in a separate patch. If you send a v2 with the return NULL fixed
up, I'll base my patch (to add a retval check) on yours.

Kind regards,
Peter

> > 
> > >  }
> > >  
> > > @@ -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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