ALSA: seq: Check the conflicting port at port creation

We didn't check if a port with the given port number has been already
present at creating a new port.  Check it and return -EBUSY properly
if the port number conflicts.
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230523075358.9672-22-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/seq_clientmgr.c

@@ -1194,15 +1194,19 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client, void *arg)
 	struct snd_seq_port_info *info = arg;
 	struct snd_seq_client_port *port;
 	struct snd_seq_port_callback *callback;
-	int port_idx;
+	int port_idx, err;
 
 	/* it is not allowed to create the port for an another client */
 	if (info->addr.client != client->number)
 		return -EPERM;
 
-	port = snd_seq_create_port(client, (info->flags & SNDRV_SEQ_PORT_FLG_GIVEN_PORT) ? info->addr.port : -1);
-	if (port == NULL)
-		return -ENOMEM;
+	if (info->flags & SNDRV_SEQ_PORT_FLG_GIVEN_PORT)
+		port_idx = info->addr.port;
+	else
+		port_idx = -1;
+	err = snd_seq_create_port(client, port_idx, &port);
+	if (err < 0)
+		return err;
 
 	if (client->type == USER_CLIENT && info->kernel) {
 		port_idx = port->addr.port;

sound/core/seq/seq_ports.c

@@ -107,33 +107,34 @@ static void port_subs_info_init(struct snd_seq_port_subs_info *grp)
 }
 
 
-/* create a port, port number is returned (-1 on failure);
+/* create a port, port number or a negative error code is returned
  * the caller needs to unref the port via snd_seq_port_unlock() appropriately
  */
-struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
-						int port)
+int snd_seq_create_port(struct snd_seq_client *client, int port,
+			struct snd_seq_client_port **port_ret)
 {
 	struct snd_seq_client_port *new_port, *p;
-	int num = -1;
+	int num;
 	
+	*port_ret = NULL;
+
 	/* sanity check */
 	if (snd_BUG_ON(!client))
-		return NULL;
+		return -EINVAL;
 
 	if (client->num_ports >= SNDRV_SEQ_MAX_PORTS) {
 		pr_warn("ALSA: seq: too many ports for client %d\n", client->number);
-		return NULL;
+		return -EINVAL;
 	}
 
 	/* create a new port */
 	new_port = kzalloc(sizeof(*new_port), GFP_KERNEL);
 	if (!new_port)
-		return NULL;	/* failure, out of memory */
+		return -ENOMEM;	/* failure, out of memory */
 	/* init port data */
 	new_port->addr.client = client->number;
 	new_port->addr.port = -1;
 	new_port->owner = THIS_MODULE;
-	sprintf(new_port->name, "port-%d", num);
 	snd_use_lock_init(&new_port->use_lock);
 	port_subs_info_init(&new_port->c_src);
 	port_subs_info_init(&new_port->c_dest);
@@ -143,6 +144,10 @@ struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
 	mutex_lock(&client->ports_mutex);
 	write_lock_irq(&client->ports_lock);
 	list_for_each_entry(p, &client->ports_list_head, list) {
+		if (p->addr.port == port) {
+			num = -EBUSY;
+			goto unlock;
+		}
 		if (p->addr.port > num)
 			break;
 		if (port < 0) /* auto-probe mode */
@@ -153,10 +158,12 @@ struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
 	client->num_ports++;
 	new_port->addr.port = num;	/* store the port number in the port */
 	sprintf(new_port->name, "port-%d", num);
+	*port_ret = new_port;
+ unlock:
 	write_unlock_irq(&client->ports_lock);
 	mutex_unlock(&client->ports_mutex);
 
-	return new_port;
+	return num;
 }
 
 /* */

sound/core/seq/seq_ports.h

@@ -86,8 +86,9 @@ struct snd_seq_client_port *snd_seq_port_query_nearest(struct snd_seq_client *cl
 /* unlock the port */
 #define snd_seq_port_unlock(port) snd_use_lock_free(&(port)->use_lock)
 
-/* create a port, port number is returned (-1 on failure) */
-struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client, int port_index);
+/* create a port, port number or a negative error code is returned */
+int snd_seq_create_port(struct snd_seq_client *client, int port_index,
+			struct snd_seq_client_port **port_ret);
 
 /* delete a port */
 int snd_seq_delete_port(struct snd_seq_client *client, int port);