linux-kernel - Re: [PATCH] usb: gadget: f_hid: fix endianness issue with descriptors

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Date:   Mon, 21 Jun 2021 11:22:36 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Ruslan Bilovol <ruslan.bilovol@...il.com>,
        Felipe Balbi <balbi@...nel.org>,
        Fabien Chouteau <fabien.chouteau@...co.com>,
        Segiy Stetsyuk <serg_stetsuk@....net>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...nel.org
Subject: Re: [PATCH] usb: gadget: f_hid: fix endianness issue with descriptors

On Thu, Jun 17, 2021 at 07:44:21PM -0400, Alan Stern wrote:
> On Thu, Jun 17, 2021 at 06:52:54PM +0200, Greg Kroah-Hartman wrote:
> > On Thu, Jun 17, 2021 at 07:27:55PM +0300, Ruslan Bilovol wrote:
> > > Running sparse checker it shows warning message about
> > > incorrect endianness used for descriptor initialization:
> > > 
> > > | f_hid.c:91:43: warning: incorrect type in initializer (different base types)
> > > | f_hid.c:91:43:    expected restricted __le16 [usertype] bcdHID
> > > | f_hid.c:91:43:    got int
> > > 
> > > Fixing issue with cpu_to_le16() macro
> > > 
> > > Fixes: 71adf1189469 ("USB: gadget: add HID gadget driver")
> > > Cc: Fabien Chouteau <fabien.chouteau@...co.com>
> > > Cc: Segiy Stetsyuk <serg_stetsuk@....net>
> > > Cc: stable@...nel.org
> > > Signed-off-by: Ruslan Bilovol <ruslan.bilovol@...il.com>
> > > ---
> > >  drivers/usb/gadget/function/f_hid.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
> > > index 70774d8cb14e..02683ac0719d 100644
> > > --- a/drivers/usb/gadget/function/f_hid.c
> > > +++ b/drivers/usb/gadget/function/f_hid.c
> > > @@ -88,7 +88,7 @@ static struct usb_interface_descriptor hidg_interface_desc = {
> > >  static struct hid_descriptor hidg_desc = {
> > >  	.bLength			= sizeof hidg_desc,
> > >  	.bDescriptorType		= HID_DT_HID,
> > > -	.bcdHID				= 0x0101,
> > > +	.bcdHID				= cpu_to_le16(0x0101),
> > 
> > This is a BCD value, not a little-endian value, are you sure this
> > conversion is correct?
> 
> It's a BCD value, but the storage format is little endian.  So yes, the 
> conversion is correct.
> 
> But even more, the conversion is correct because 0x0101 yields exactly 
> the same sequence of bytes in little-endian and big-endian orders!  
> Either way, it is two bytes each containing 0x01.

Ah, which is why no one has noticed this yet :)

I'll go apply this just to be "correct".

thanks,

greg k-h