usb: core: stop USB enumeration if too many retries

When a broken USB accessory connects to a USB host, usbcore might
keep doing enumeration retries. If the host has a watchdog mechanism,
the kernel panic will happen on the host.

This patch provides an attribute early_stop to limit the numbers of retries
for each port of a hub. If a port was marked with early_stop attribute,
unsuccessful connection attempts will fail quickly. In addition, if an
early_stop port has failed to initialize, it will ignore all future
connection events until early_stop attribute is clear.

Signed-off-by: Ray Chi <[e-mail]>
Reviewed-by: Alan Stern <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-bus-usb

···
 		attached to the port will not be detected, initialized,
 		or enumerated.
 
+What:		/sys/bus/usb/devices/.../<hub_interface>/port<X>/early_stop
+Date:		Sep 2022
+Contact:	Ray Chi <[e-mail]>
+Description:
+		Some USB hosts have some watchdog mechanisms so that the device
+		may enter ramdump if it takes a long time during port initialization.
+		This attribute allows each port just has two attempts so that the
+		port initialization will be failed quickly. In addition, if a port
+		which is marked with early_stop has failed to initialize, it will ignore
+		all future connections until this attribute is clear.
+
 What:		/sys/bus/usb/devices/.../power/usb2_lpm_l1_timeout
 Date:		May 2013
 Contact:	Mathias Nyman <[e-mail]>

drivers/usb/core/hub.c

···
 	return status;
 }
 
+/*
+ * hub_port_stop_enumerate - stop USB enumeration or ignore port events
+ * @hub: target hub
+ * @port1: port num of the port
+ * @retries: port retries number of hub_port_init()
+ *
+ * Return:
+ *    true: ignore port actions/events or give up connection attempts.
+ *    false: keep original behavior.
+ *
+ * This function will be based on retries to check whether the port which is
+ * marked with early_stop attribute would stop enumeration or ignore events.
+ *
+ * Note:
+ * This function didn't change anything if early_stop is not set, and it will
+ * prevent all connection attempts when early_stop is set and the attempts of
+ * the port are more than 1.
+ */
+static bool hub_port_stop_enumerate(struct usb_hub *hub, int port1, int retries)
+{
+	struct usb_port *port_dev = hub->ports[port1 - 1];
+
+	if (port_dev->early_stop) {
+		if (port_dev->ignore_event)
+			return true;
+
+		/*
+		 * We want unsuccessful attempts to fail quickly.
+		 * Since some devices may need one failure during
+		 * port initialization, we allow two tries but no
+		 * more.
+		 */
+		if (retries < 2)
+			return false;
+
+		port_dev->ignore_event = 1;
+	} else
+		port_dev->ignore_event = 0;
+
+	return port_dev->ignore_event;
+}
+
 /* Check if a port is power on */
 int usb_port_is_power_on(struct usb_hub *hub, unsigned int portstatus)
 {
···
 	do_new_scheme = use_new_scheme(udev, retry_counter, port_dev);
 
 	for (retries = 0; retries < GET_DESCRIPTOR_TRIES; (++retries, msleep(100))) {
+		if (hub_port_stop_enumerate(hub, port1, retries)) {
+			retval = -ENODEV;
+			break;
+		}
+
 		if (do_new_scheme) {
 			struct usb_device_descriptor *buf;
 			int r = 0;
···
 	status = 0;
 
 	for (i = 0; i < PORT_INIT_TRIES; i++) {
+		if (hub_port_stop_enumerate(hub, port1, i)) {
+			status = -ENODEV;
+			break;
+		}
+
 		usb_lock_port(port_dev);
 		mutex_lock(hcd->address0_mutex);
 		retry_locked = true;
···
 	if (!pm_runtime_active(&port_dev->dev))
 		return;
 
+	/* skip port actions if ignore_event and early_stop are true */
+	if (port_dev->ignore_event && port_dev->early_stop)
+		return;
+
 	if (hub_handle_remote_wakeup(hub, port1, portstatus, portchange))
 		connect_change = 1;
 
···
 	mutex_lock(hcd->address0_mutex);
 
 	for (i = 0; i < PORT_INIT_TRIES; ++i) {
+		if (hub_port_stop_enumerate(parent_hub, port1, i)) {
+			ret = -ENODEV;
+			break;
+		}
 
 		/* ep0 maxpacket size may change; let the HCD know about it.
 		 * Other endpoints will be handled by re-enumeration. */

drivers/usb/core/hub.h

···
  * @is_superspeed cache super-speed status
  * @usb3_lpm_u1_permit: whether USB3 U1 LPM is permitted.
  * @usb3_lpm_u2_permit: whether USB3 U2 LPM is permitted.
+ * @early_stop: whether port initialization will be stopped earlier.
+ * @ignore_event: whether events of the port are ignored.
  */
 struct usb_port {
 	struct usb_device *child;
···
 	u32 over_current_count;
 	u8 portnum;
 	u32 quirks;
+	unsigned int early_stop:1;
+	unsigned int ignore_event:1;
 	unsigned int is_superspeed:1;
 	unsigned int usb3_lpm_u1_permit:1;
 	unsigned int usb3_lpm_u2_permit:1;

drivers/usb/core/port.c

···
 
 static const struct attribute_group *port_dev_group[];
 
+static ssize_t early_stop_show(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	struct usb_port *port_dev = to_usb_port(dev);
+
+	return sysfs_emit(buf, "%s\n", port_dev->early_stop ? "yes" : "no");
+}
+
+static ssize_t early_stop_store(struct device *dev, struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct usb_port *port_dev = to_usb_port(dev);
+	bool value;
+
+	if (kstrtobool(buf, &value))
+		return -EINVAL;
+
+	if (value)
+		port_dev->early_stop = 1;
+	else
+		port_dev->early_stop = 0;
+
+	return count;
+}
+static DEVICE_ATTR_RW(early_stop);
+
 static ssize_t disable_show(struct device *dev,
 			      struct device_attribute *attr, char *buf)
 {
···
 	&dev_attr_quirks.attr,
 	&dev_attr_over_current_count.attr,
 	&dev_attr_disable.attr,
+	&dev_attr_early_stop.attr,
 	NULL,
 };