Re: [PATCH] USB: Always select config with the highest supported UAC version

[Alexander Tsoy <alexander@tsoy.me>]

В Вт, 13/02/2024 в 12:05 +0100, Greg Kroah-Hartman пишет:
> On Mon, Feb 12, 2024 at 06:28:48PM +0300, Alexander Tsoy wrote:
> > Config with the highest supported UAC version is always preferable
> > because
> > it usually provides more features.
> > 
> > Main motivation for this change is to improve support for several
> > UAC2
> > devices which have UAC1 config as the first one for compatibility
> > reasons.
> > UAC2 mode provides a wider range of supported sampling rates on
> > these
> > devices. Also when UAC4 support is implemented, it will need just
> > one
> > additional case line without changing the logic.
> > 
> > Signed-off-by: Alexander Tsoy <alexander@tsoy.me>
> > ---
> >  drivers/usb/core/generic.c | 39 +++++++++++++++++++++++++---------
> > ----
> >  1 file changed, 26 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/usb/core/generic.c
> > b/drivers/usb/core/generic.c
> > index b134bff5c3fe..8aeb180e1cf9 100644
> > --- a/drivers/usb/core/generic.c
> > +++ b/drivers/usb/core/generic.c
> > @@ -48,9 +48,16 @@ static bool is_audio(struct
> > usb_interface_descriptor *desc)
> >  	return desc->bInterfaceClass == USB_CLASS_AUDIO;
> >  }
> >  
> > -static bool is_uac3_config(struct usb_interface_descriptor *desc)
> > +static bool is_supported_uac(struct usb_interface_descriptor
> > *desc)
> >  {
> > -	return desc->bInterfaceProtocol == UAC_VERSION_3;
> > +	switch(desc->bInterfaceProtocol) {
> > +	case UAC_VERSION_1:
> > +	case UAC_VERSION_2:
> > +	case UAC_VERSION_3:
> > +		return true;
> > +	default:
> > +		return false;
> > +	}
> >  }
> >  
> >  int usb_choose_configuration(struct usb_device *udev)
> > @@ -135,22 +142,28 @@ int usb_choose_configuration(struct
> > usb_device *udev)
> >  		}
> >  
> >  		/*
> > -		 * Select first configuration as default for audio
> > so that
> > -		 * devices that don't comply with UAC3 protocol
> > are supported.
> > -		 * But, still iterate through other configurations
> > and
> > -		 * select UAC3 compliant config if present.
> > +		 * Iterate through audio configurations and select
> > the first of
> > +		 * the highest supported UAC versions. Select the
> > first config
> > +		 * if no supported UAC configs are found.
> >  		 */
> >  		if (desc && is_audio(desc)) {
> > -			/* Always prefer the first found UAC3
> > config */
> > -			if (is_uac3_config(desc)) {
> > -				best = c;
> > -				break;
> > -			}
> > +			struct
> > usb_interface_descriptor	*best_desc = NULL;
> > +
> > +			if (best)
> > +				best_desc = &best->intf_cache[0]-
> > >altsetting->desc;
> 
> Are you sure you always have a intf_cache[0] pointer?  What about
> altsetting?  Remember, invalid descriptors happen all the time, and
> are
> a known "attack vector" against the USB stack.
> 
> 

Well, similar code exists at the beginning of the loop. But I just
discovered that according to the Backwards Compatibility sections of
UAC 3.0 and UAC 4.0 specs, we need to look at the bFunctionProtocol
field of the Interface Association descriptor. So the current code that
selects UAC3 configuration is also not entirely correct AFAIS.