[PATCH v3] usb: core: Prevent null pointer dereference in update_port_device_state

[Udipto Goswami <quic_ugoswami@quicinc.com>]

Currently,the function update_port_device_state gets the usb_hub from
udev->parent by calling usb_hub_to_struct_hub.
However, in case the actconfig or the maxchild is 0, the usb_hub would
be NULL and upon further accessing to get port_dev would result in null
pointer dereference.

Fix this by introducing an if check after the usb_hub is populated.

Fixes: 83cb2604f641 ("usb: core: add sysfs entry for usb device state")
Cc: stable@vger.kernel.org
Signed-off-by: Udipto Goswami <quic_ugoswami@quicinc.com>
---
v3: Re-wrote the comment for better context.
v2: Introduced comment for the if check & CC'ed stable.

 drivers/usb/core/hub.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index ffd7c99e24a3..6b514546e59b 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2053,9 +2053,23 @@ static void update_port_device_state(struct usb_device *udev)
 
 	if (udev->parent) {
 		hub = usb_hub_to_struct_hub(udev->parent);
-		port_dev = hub->ports[udev->portnum - 1];
-		WRITE_ONCE(port_dev->state, udev->state);
-		sysfs_notify_dirent(port_dev->state_kn);
+
+		/*
+		 * The Link Layer Validation System Driver (lvstest)
+		 * has procedure of unbinding the hub before running
+		 * the rest of the procedure. This triggers
+		 * hub_disconnect will set the hub's maxchild to 0.
+		 * This would result usb_hub_to_struct_hub in this
+		 * function to return NULL.
+		 *
+		 * Add if check to avoid running into NULL pointer
+		 * de-reference.
+		 */
+		if (hub) {
+			port_dev = hub->ports[udev->portnum - 1];
+			WRITE_ONCE(port_dev->state, udev->state);
+			sysfs_notify_dirent(port_dev->state_kn);
+		}
 	}
 }
 
-- 
2.17.1