usb: gadget: f_midi: Fix memleak in f_midi_alloc

In the error path, if midi is not null, we should
free the midi->id if necessary to prevent memleak.

Fixes: b85e9de ("usb: gadget: f_midi: convert to new function interface with backward compatibility")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Link: https://lore.kernel.org/r/20201117021629.1470544-2-zhangqilong3@huawei.com
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Zhang Qilong

drivers/usb/gadget/function/f_midi.c

@@ -1315,7 +1315,7 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
 	midi->id = kstrdup(opts->id, GFP_KERNEL);
 	if (opts->id && !midi->id) {
 		status = -ENOMEM;
-		goto setup_fail;
+		goto midi_free;
 	}
 	midi->in_ports = opts->in_ports;
 	midi->out_ports = opts->out_ports;
@@ -1327,7 +1327,7 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
 
 	status = kfifo_alloc(&midi->in_req_fifo, midi->qlen, GFP_KERNEL);
 	if (status)
-		goto setup_fail;
+		goto midi_free;
 
 	spin_lock_init(&midi->transmit_lock);
 
@@ -1343,9 +1343,13 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
 
 	return &midi->func;
 
+midi_free:
+	if (midi)
+		kfree(midi->id);
+	kfree(midi);
 setup_fail:
 	mutex_unlock(&opts->lock);
-	kfree(midi);
+
 	return ERR_PTR(status);
 }