ALSA: usb-mixer: us16x08: validate meter packet indices

ALSA: usb-mixer: us16x08: validate meter packet indices

get_meter_levels_from_urb() parses the 64-byte meter packets sent by
the device and fills the per-channel arrays meter_level[],
comp_level[] and master_level[] in struct snd_us16x08_meter_store.

Currently the function derives the channel index directly from the
meter packet (MUB2(meter_urb, s) - 1) and uses it to index those
arrays without validating the range. If the packet contains a
negative or out-of-range channel number, the driver may write past
the end of these arrays.

Introduce a local channel variable and validate it before updating the
arrays. We reject negative indices, limit meter_level[] and
comp_level[] to SND_US16X08_MAX_CHANNELS, and guard master_level[]
updates with ARRAY_SIZE(master_level).

Fixes: d2bb390a2081 ("ALSA: usb-audio: Tascam US-16x08 DSP mixer quirk")
Reported-by: DARKNAVY (@DarkNavyOrg) <vr@darknavy.com>
Closes: https://lore.kernel.org/tencent_21C112743C44C1A2517FF219@qq.com
Signed-off-by: Shipei Qu <qu@darknavy.com>
Link: https://patch.msgid.link/20251217024630.59576-1-qu@darknavy.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>