Re: [PATCH v2] ALSA: usb-audio: validate full match when resolving quirk aliases

[Takashi Iwai <tiwai@suse.de>]

On Tue, 17 Mar 2026 18:35:16 +0100,
Cássio Gabriel wrote:
> 
> On Tue, Mar 17, 2026 at 10:03:10AM +0100, Takashi Iwai wrote:
> > On Tue, 17 Mar 2026 05:22:04 +0100,
> > Cássio Gabriel wrote:
> > > 
> > > get_alias_quirk() resolves a quirk for an aliased USB ID by scanning
> > > usb_audio_ids[], but it currently checks only the vendor/product pair.
> > > 
> > > This is weak for quirk table entries that also depend on additional
> > > USB_DEVICE_ID match fields, such as device or interface class,
> > > subclass, protocol, interface number, or bcdDevice range.
> > > 
> > > Rework the alias lookup so that it still uses the aliased vid:pid as
> > > the initial lookup key, but validates the remaining match_flags
> > > constraints of each candidate entry against the real device and
> > > interface descriptors before returning the quirk.
> > > 
> > > Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
> > > ---
> > > Changes in v2:
> > > - drop the temporary usb_device_id reconstruction approach
> > > - validate only the remaining match_flags explicitly
> > > - pass struct usb_interface * to get_alias_quirk()
> > > - Link to v1: https://lore.kernel.org/r/20260314-alsa-usb-fix-quirk-alias-v1-1-3269998f7ada@gmail.com
> > > ---
> > >  sound/usb/card.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++-------
> > >  1 file changed, 64 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/sound/usb/card.c b/sound/usb/card.c
> > > index fd81f32a66fb..153085a77d43 100644
> > > --- a/sound/usb/card.c
> > > +++ b/sound/usb/card.c
> > > @@ -864,21 +864,77 @@ static void find_last_interface(struct snd_usb_audio *chip)
> > >  	usb_audio_dbg(chip, "Found last interface = %d\n", chip->last_iface);
> > >  }
> > >  
> > > +/*
> > > + * Match aliased vid:pid first, then validate remaining fields against
> > > + * the real device and interface descriptors.
> > > + */
> > > +static bool snd_usb_match_alias_entry(struct usb_interface *intf,
> > > +				      const struct usb_device_id *id,
> > > +				      u32 alias_id)
> > > +{
> > > +	struct usb_device *dev = interface_to_usbdev(intf);
> > > +	const struct usb_host_interface *alt = intf->cur_altsetting;
> > > +	const struct usb_interface_descriptor *intfd = &alt->desc;
> > > +	const struct usb_device_descriptor *devd = &dev->descriptor;
> > > +	u16 bcd = le16_to_cpu(devd->bcdDevice);
> > > +
> > > +	/* Match aliased vendor/product */
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_VENDOR) &&
> > > +	    id->idVendor != USB_ID_VENDOR(alias_id))
> > > +		return false;
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_PRODUCT) &&
> > > +	    id->idProduct != USB_ID_PRODUCT(alias_id))
> > > +		return false;
> > > +	/* Match real device descriptor constraints */
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_LO) &&
> > > +	    bcd < id->bcdDevice_lo)
> > > +		return false;
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_HI) &&
> > > +	    bcd > id->bcdDevice_hi)
> > > +		return false;
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_CLASS) &&
> > > +	    devd->bDeviceClass != id->bDeviceClass)
> > > +		return false;
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_SUBCLASS) &&
> > > +	    devd->bDeviceSubClass != id->bDeviceSubClass)
> > > +		return false;
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_PROTOCOL) &&
> > > +	    devd->bDeviceProtocol != id->bDeviceProtocol)
> > > +		return false;
> > > +	/* Match real interface descriptor constraints */
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_CLASS) &&
> > > +	    intfd->bInterfaceClass != id->bInterfaceClass)
> > > +		return false;
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_SUBCLASS) &&
> > > +	    intfd->bInterfaceSubClass != id->bInterfaceSubClass)
> > > +		return false;
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_PROTOCOL) &&
> > > +	    intfd->bInterfaceProtocol != id->bInterfaceProtocol)
> > > +		return false;
> > > +	if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_NUMBER) &&
> > > +	    intfd->bInterfaceNumber != id->bInterfaceNumber)
> > > +		return false;
> > > +
> > > +	return true;
> > > +}
> > 
> > Hrm, it became larger than I wished.
> > You compared with another implementation and decided to choose this
> > version?
> > 
> 
> Hi,
> 
> I went with the explicit matching path in v2 because I wanted to keep
> the alias lookup based on the aliased vid:pid while validating the
> remaining match_flags against the real descriptors.
> 
> > An alternative would be to have a copy of usb_device_id like your
> > previous version, and clear match_flags bits with
> > ~USB_DEVICE_ID_MATCH_DEVICE.  If match_flags becomes 0, it passes.
> > Otherwise call usb_match_one_id().
> 
> thanks, that makes sense.
> 
> What do you think about this approach?
> ```
> static const struct snd_usb_audio_quirk *
> get_alias_quirk(struct usb_interface *intf, unsigned int id)
> {
>         const struct usb_device_id *p;
>         struct usb_device_id match_id;
> 
>         for (p = usb_audio_ids; p->match_flags; p++) {
>                 if ((p->match_flags & USB_DEVICE_ID_MATCH_DEVICE) !=
>                     USB_DEVICE_ID_MATCH_DEVICE)
>                         continue;
> 
>                 if (p->idVendor != USB_ID_VENDOR(id) ||
>                     p->idProduct != USB_ID_PRODUCT(id))
>                         continue;
> 
>                 match_id = *p;
>                 match_id.match_flags &= ~USB_DEVICE_ID_MATCH_DEVICE;
>                 if (!match_id.match_flags || usb_match_one_id(intf, &match_id))
>                         return (const struct snd_usb_audio_quirk *)
>                                 p->driver_info;
>         }
> 
>         return NULL;
> }
> ```

Yes, that's what I had in mind.


thanks,

Takashi