ALSA: usb-audio: Don't create a mixer element with bogus volume range

Some USB-audio descriptors provide a bogus volume range (e.g. volume
min and max are identical), which confuses user-space.
This patch makes the driver skipping such a control element.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206221
Link: https://lore.kernel.org/r/20200214144928.23628-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index d659fdb475e2bc373941df884b0404364cfb534b..96e20488804d1c5202d9883fd05b1cad0e0def2d 100644 (file)
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1666,6 +1666,16 @@ static void __build_feature_ctl(struct usb_mixer_interface *mixer,
        /* get min/max values */
        get_min_max_with_quirks(cval, 0, kctl);
 
+       /* skip a bogus volume range */
+       if (cval->max <= cval->min) {
+               usb_audio_dbg(mixer->chip,
+                             "[%d] FU [%s] skipped due to invalid volume\n",
+                             cval->head.id, kctl->id.name);
+               snd_ctl_free_one(kctl);
+               return;
+       }
+
+
        if (control == UAC_FU_VOLUME) {
                check_mapped_dB(map, cval);
                if (cval->dBmin < cval->dBmax || !cval->initialized) {