USB: usbtmc can do IO to device after disconnect

usbtmc will happily complete read/write requests even after disconnect
has returned. The fix is to introduce a flag.
Signed-off-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/class/usbtmc.c

@@ -86,6 +86,8 @@ struct usbtmc_device_data {
 	bool TermCharEnabled;
 	bool auto_abort;
 
+	bool zombie; /* fd of disconnected device */
+
 	struct usbtmc_dev_capabilities	capabilities;
 	struct kref kref;
 	struct mutex io_mutex;	/* only one i/o function running at a time */
@@ -384,6 +386,10 @@ static ssize_t usbtmc_read(struct file *filp, char __user *buf,
 		return -ENOMEM;
 
 	mutex_lock(&data->io_mutex);
+	if (data->zombie) {
+		retval = -ENODEV;
+		goto exit;
+	}
 
 	remaining = count;
 	done = 0;
@@ -496,6 +502,10 @@ static ssize_t usbtmc_write(struct file *filp, const char __user *buf,
 		return -ENOMEM;
 
 	mutex_lock(&data->io_mutex);
+	if (data->zombie) {
+		retval = -ENODEV;
+		goto exit;
+	}
 
 	remaining = count;
 	done = 0;
@@ -925,6 +935,10 @@ static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 	data = file->private_data;
 	mutex_lock(&data->io_mutex);
+	if (data->zombie) {
+		retval = -ENODEV;
+		goto skip_io_on_zombie;
+	}
 
 	switch (cmd) {
 	case USBTMC_IOCTL_CLEAR_OUT_HALT:
@@ -952,6 +966,7 @@ static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		break;
 	}
 
+skip_io_on_zombie:
 	mutex_unlock(&data->io_mutex);
 	return retval;
 }
@@ -995,6 +1010,7 @@ static int usbtmc_probe(struct usb_interface *intf,
 	usb_set_intfdata(intf, data);
 	kref_init(&data->kref);
 	mutex_init(&data->io_mutex);
+	data->zombie = 0;
 
 	/* Initialize USBTMC bTag and other fields */
 	data->bTag	= 1;
@@ -1065,6 +1081,9 @@ static void usbtmc_disconnect(struct usb_interface *intf)
 	usb_deregister_dev(intf, &usbtmc_class);
 	sysfs_remove_group(&intf->dev.kobj, &capability_attr_grp);
 	sysfs_remove_group(&intf->dev.kobj, &data_attr_grp);
+	mutex_lock(&data->io_mutex);
+	data->zombie = 1;
+	mutex_unlock(&data->io_mutex);
 	kref_put(&data->kref, usbtmc_delete);
 }