usb: core : hub: Fix BOS 'NULL pointer' kernel panic

When a USB 3.0 mass storage device is disconnected in transporting
state, storage device driver may handle it as a transport error and
reset the device by invoking usb_reset_and_verify_device()
and following could happen:

in usb_reset_and_verify_device():
   udev->bos = NULL;

For U1/U2 enabled devices, driver will disable LPM, and in some
conditions:
   from usb_unlocked_disable_lpm()
    --> usb_disable_lpm()
    --> usb_enable_lpm()
        udev->bos->ss_cap->bU1devExitLat;

And it causes 'NULL pointer' and 'kernel panic':

[  157.976257] Unable to handle kernel NULL pointer dereference
at virtual address 00000010
...
[  158.026400] PC is at usb_enable_link_state+0x34/0x2e0
[  158.031442] LR is at usb_enable_lpm+0x98/0xac
...
[  158.137368] [<ffffffc0006a1cac>] usb_enable_link_state+0x34/0x2e0
[  158.143451] [<ffffffc0006a1fec>] usb_enable_lpm+0x94/0xac
[  158.148840] [<ffffffc0006a20e8>] usb_disable_lpm+0xa8/0xb4
...
[  158.214954] Kernel panic - not syncing: Fatal exception

This commit moves 'udev->bos = NULL' behind usb_unlocked_disable_lpm()
to prevent from NULL pointer access.

Issue can be reproduced by following setup:
1) A SS pen drive behind a SS hub connected to the host.
2) Transporting data between the pen drive and the host.
3) Abruptly disconnect hub and pen drive from host.
4) With a chance it crashes.
Signed-off-by: Hans Yang <hansy@nvidia.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hub.c

@@ -5326,9 +5326,6 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
 	if (udev->usb2_hw_lpm_enabled == 1)
 		usb_set_usb2_hardware_lpm(udev, 0);
 
-	bos = udev->bos;
-	udev->bos = NULL;
-
 	/* Disable LPM and LTM while we reset the device and reinstall the alt
 	 * settings.  Device-initiated LPM settings, and system exit latency
 	 * settings are cleared when the device is reset, so we have to set
@@ -5337,15 +5334,18 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
 	ret = usb_unlocked_disable_lpm(udev);
 	if (ret) {
 		dev_err(&udev->dev, "%s Failed to disable LPM\n.", __func__);
-		goto re_enumerate;
+		goto re_enumerate_no_bos;
 	}
 	ret = usb_disable_ltm(udev);
 	if (ret) {
 		dev_err(&udev->dev, "%s Failed to disable LTM\n.",
 				__func__);
-		goto re_enumerate;
+		goto re_enumerate_no_bos;
 	}
 
+	bos = udev->bos;
+	udev->bos = NULL;
+
 	for (i = 0; i < SET_CONFIG_TRIES; ++i) {
 
 		/* ep0 maxpacket size may change; let the HCD know about it.
@@ -5442,10 +5442,11 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
 	return 0;
 
 re_enumerate:
-	/* LPM state doesn't matter when we're about to destroy the device. */
-	hub_port_logical_disconnect(parent_hub, port1);
 	usb_release_bos_descriptor(udev);
 	udev->bos = bos;
+re_enumerate_no_bos:
+	/* LPM state doesn't matter when we're about to destroy the device. */
+	hub_port_logical_disconnect(parent_hub, port1);
 	return -ENODEV;
 }