linux-kernel - Re: [PATCH v3] HID: keep dev_rdesc unmodified and use it for comparisons

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Message-ID: <20120920204825.GA2455@polaris.bitmath.org>
Date:	Thu, 20 Sep 2012 22:48:25 +0200
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Kevin Daughtridge <kevin@...u.com>
Cc:	linux-input@...r.kernel.org, jkosina@...e.cz,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v3] HID: keep dev_rdesc unmodified and use it for
 comparisons

> The dev_rdesc member of the hid_device structure is meant to store the original
> report descriptor received from the device, but it is currently passed to any
> report_fixup method before it is copied to the rdesc member. This patch uses a
> temporary buffer to shield dev_rdesc from the side effects of many HID drivers'
> report_fixup implementations.
> 
> usbhid's hid_post_reset checks the report descriptor currently returned by the
> device against a descriptor that may have been modified by a driver's
> report_fixup method. That leaves some devices nonfunctional after a resume, with
> a "reset_resume error 1" reported. This patch checks the new descriptor against
> the unmodified dev_rdesc instead and uses the original, instead of modified,
> report size.
> 
> BugLink: http://bugs.launchpad.net/bugs/1049623
> Signed-off-by: Kevin Daughtridge <kevin@...u.com>
> ---

Looks like it will work, thank you Kevin. The comments below are just
suggestions, I am fine with the patch as is.


>  drivers/hid/hid-core.c        |   16 +++++++++++++---
>  drivers/hid/usbhid/hid-core.c |    6 +++---
>  2 files changed, 16 insertions(+), 6 deletions(-)
> 
> Changed in this version: added a temporary buffer to work around report_fixup
> inconsistencies; using dev_rsize instead of rsize to allocate and read new
> descriptor.
> 
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index 8bcd168..5de3bb3 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -757,6 +757,7 @@ int hid_open_report(struct hid_device *device)
>  	struct hid_item item;
>  	unsigned int size;
>  	__u8 *start;
> +	__u8 *buf;

It is sad to have to add a temporary here.

>  	__u8 *end;
>  	int ret;
>  	static int (*dispatch_type[])(struct hid_parser *parser,
> @@ -775,12 +776,21 @@ int hid_open_report(struct hid_device *device)
>  		return -ENODEV;
>  	size = device->dev_rsize;
>  
> +	buf = kmemdup(start, size, GFP_KERNEL);
> +	if (buf == NULL)
> +		return -ENOMEM;
> +
>  	if (device->driver->report_fixup)
> -		start = device->driver->report_fixup(device, start, &size);
> +		start = device->driver->report_fixup(device, buf, &size);
> +	else
> +		start = buf;
>  
> -	device->rdesc = kmemdup(start, size, GFP_KERNEL);
> -	if (device->rdesc == NULL)
> +	start = kmemdup(start, size, GFP_KERNEL);
> +	kfree(buf);

Changing the semantics of the callback did not seem appealing, but it
does not prevent us from using our own version internally. So, how
about something like this:

   static __u8 *hid_alloc_rdesc(struct hid_device *devicew,
   			     const __u8 *start, unsigned int *size)
   {
   	__u8 *rdesc = kmemdup(start, *size, GFP_KERNEL);
   
   	if (rdesc && device->driver->report_fixup) {
   		__u8 *tmp = device->driver->report_fixup(device, rdesc, size);
   
   		if (tmp != rdesc) {
   			tmp = kmemdup(tmp, *size, GFP_KERNEL);
   			kfree(rdesc);
   			rdesc = tmp;
   		}
   	}
   
   	return rdesc;
   }


> +	if (start == NULL)
>  		return -ENOMEM;
> +
> +	device->rdesc = start;
>  	device->rsize = size;
>  
>  	parser = vzalloc(sizeof(struct hid_parser));
> diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
> index dedd8e4..8e0c4bf94 100644
> --- a/drivers/hid/usbhid/hid-core.c
> +++ b/drivers/hid/usbhid/hid-core.c
> @@ -1415,20 +1415,20 @@ static int hid_post_reset(struct usb_interface *intf)
>  	 * configuration descriptors passed, we already know that
>  	 * the size of the HID report descriptor has not changed.
>  	 */
> -	rdesc = kmalloc(hid->rsize, GFP_KERNEL);
> +	rdesc = kmalloc(hid->dev_rsize, GFP_KERNEL);
>  	if (!rdesc) {
>  		dbg_hid("couldn't allocate rdesc memory (post_reset)\n");
>  		return 1;
>  	}
>  	status = hid_get_class_descriptor(dev,
>  				interface->desc.bInterfaceNumber,
> -				HID_DT_REPORT, rdesc, hid->rsize);
> +				HID_DT_REPORT, rdesc, hid->dev_rsize);
>  	if (status < 0) {
>  		dbg_hid("reading report descriptor failed (post_reset)\n");
>  		kfree(rdesc);
>  		return 1;
>  	}
> -	status = memcmp(rdesc, hid->rdesc, hid->rsize);
> +	status = memcmp(rdesc, hid->dev_rdesc, hid->dev_rsize);
>  	kfree(rdesc);
>  	if (status != 0) {
>  		dbg_hid("report descriptor changed\n");

Thanks,
Henrik
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