ALSA: caiaq: fix stack out-of-bounds read in init_card

The loop creates a whitespace-stripped copy of the card shortname
where `len < sizeof(card->id)` is used for the bounds check. Since
sizeof(card->id) is 16 and the local id buffer is also 16 bytes,
writing 16 non-space characters fills the entire buffer,
overwriting the terminating nullbyte.

When this non-null-terminated string is later passed to
snd_card_set_id() -> copy_valid_id_string(), the function scans
forward with `while (*nid && ...)` and reads past the end of the
stack buffer, reading the contents of the stack.

A USB device with a product name containing many non-ASCII, non-space
characters (e.g. multibyte UTF-8) will reliably trigger this as follows:

  BUG: KASAN: stack-out-of-bounds in copy_valid_id_string
       sound/core/init.c:696 [inline]
  BUG: KASAN: stack-out-of-bounds in snd_card_set_id_no_lock+0x698/0x74c
       sound/core/init.c:718

The off-by-one has been present since commit bafeee5 ("ALSA:
snd_usb_caiaq: give better shortname") from June 2009 (v2.6.31-rc1),
which first introduced this whitespace-stripping loop. The original
code never accounted for the null terminator when bounding the copy.

Fix this by changing the loop bound to `sizeof(card->id) - 1`,
ensuring at least one byte remains as the null terminator.

Fixes: bafeee5 ("ALSA: snd_usb_caiaq: give better shortname")
Cc: stable@vger.kernel.org
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Reported-by: Berk Cem Goksel <berkcgoksel@gmail.com>
Signed-off-by: Berk Cem Goksel <berkcgoksel@gmail.com>
Link: https://patch.msgid.link/20260329133825.581585-1-berkcgoksel@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Author: berkgoksel

sound/usb/caiaq/device.c

@@ -488,7 +488,7 @@ static int init_card(struct snd_usb_caiaqdev *cdev)
 		memset(id, 0, sizeof(id));
 
 		for (c = card->shortname, len = 0;
-			*c && len < sizeof(card->id); c++)
+			*c && len < sizeof(card->id) - 1; c++)
 			if (*c != ' ')
 				id[len++] = *c;