ALSA: seq: Prohibit creating ports with special numbers

Some port numbers are special, such as 254 for subscribers and 255 for
broadcast.  Return error if application tries to create such a port.
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230523075358.9672-24-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/seq_clientmgr.c

@@ -1206,6 +1206,8 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client, void *arg)
 		port_idx = info->addr.port;
 	else
 		port_idx = -1;
+	if (port_idx >= SNDRV_SEQ_ADDRESS_UNKNOWN)
+		return -EINVAL;
 	err = snd_seq_create_port(client, port_idx, &port);
 	if (err < 0)
 		return err;