cuse: do not register multiple devices with identical names

Sysfs doesn't allow two devices with the same name, but we register a
sysfs entry for each cuse device without checking for name collisions.
This extends the registration to first check whether the name was already
registered.

To avoid race-conditions between the name-check and linking the device, we
need to protect the whole registration with a mutex.
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/cuse.c

@@ -304,14 +304,14 @@ static void cuse_gendev_release(struct device *dev)
  */
 static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 {
-	struct cuse_conn *cc = fc_to_cc(fc);
+	struct cuse_conn *cc = fc_to_cc(fc), *pos;
 	struct cuse_init_out *arg = req->out.args[0].value;
 	struct page *page = req->pages[0];
 	struct cuse_devinfo devinfo = { };
 	struct device *dev;
 	struct cdev *cdev;
 	dev_t devt;
-	int rc;
+	int rc, i;
 
 	if (req->out.h.error ||
 	    arg->major != FUSE_KERNEL_VERSION || arg->minor < 11) {
@@ -355,15 +355,24 @@ static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 	dev_set_drvdata(dev, cc);
 	dev_set_name(dev, "%s", devinfo.name);
 
+	mutex_lock(&cuse_lock);
+
+	/* make sure the device-name is unique */
+	for (i = 0; i < CUSE_CONNTBL_LEN; ++i) {
+		list_for_each_entry(pos, &cuse_conntbl[i], list)
+			if (!strcmp(dev_name(pos->dev), dev_name(dev)))
+				goto err_unlock;
+	}
+
 	rc = device_add(dev);
 	if (rc)
-		goto err_device;
+		goto err_unlock;
 
 	/* register cdev */
 	rc = -ENOMEM;
 	cdev = cdev_alloc();
 	if (!cdev)
-		goto err_device;
+		goto err_unlock;
 
 	cdev->owner = THIS_MODULE;
 	cdev->ops = &cuse_frontend_fops;
@@ -376,7 +385,6 @@ static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 	cc->cdev = cdev;
 
 	/* make the device available */
-	mutex_lock(&cuse_lock);
 	list_add(&cc->list, cuse_conntbl_head(devt));
 	mutex_unlock(&cuse_lock);
 
@@ -390,7 +398,8 @@ static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 
 err_cdev:
 	cdev_del(cdev);
-err_device:
+err_unlock:
+	mutex_unlock(&cuse_lock);
 	put_device(dev);
 err_region:
 	unregister_chrdev_region(devt, 1);