[patch added to 3.12-stable] usb: hub: do not clear BOS field during reset device

From: "Du, Changbin" <redacted>

This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.

===============

commit d8f00cd685f5c8e0def8593e520a7fef12c22407 upstream.

In function usb_reset_and_verify_device, the old BOS descriptor may
still be used before allocating a new one. (usb_unlocked_disable_lpm
function uses it under the situation that it fails to disable lpm.)
So we cannot set the udev->bos to NULL before that, just keep what it
was. It will be overwrite when allocating a new one.

Crash log:
BUG: unable to handle kernel NULL pointer dereference at
0000000000000010
IP: [<ffffffff8171f98d>] usb_enable_link_state+0x2d/0x2f0
Call Trace:
[<ffffffff8171ed5b>] ? usb_set_lpm_timeout+0x12b/0x140
[<ffffffff8171fcd1>] usb_enable_lpm+0x81/0xa0
[<ffffffff8171fdd8>] usb_disable_lpm+0xa8/0xc0
[<ffffffff8171fe1c>] usb_unlocked_disable_lpm+0x2c/0x50
[<ffffffff81723933>] usb_reset_and_verify_device+0xc3/0x710
[<ffffffff8172c4ed>] ? usb_sg_wait+0x13d/0x190
[<ffffffff81724743>] usb_reset_device+0x133/0x280
[<ffffffff8179ccd1>] usb_stor_port_reset+0x61/0x70
[<ffffffff8179cd68>] usb_stor_invoke_transport+0x88/0x520

Signed-off-by: "Du, Changbin" <redacted>
Signed-off-by: Jiri Slaby <redacted>
---
 drivers/usb/core/hub.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 3afe47870e95..040c5657582f 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c

@@ -5178,7 +5178,6 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
 		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

@@ -5287,8 +5286,11 @@ done:
 	usb_set_usb2_hardware_lpm(udev, 1);
 	usb_unlocked_enable_lpm(udev);
 	usb_enable_ltm(udev);
-	usb_release_bos_descriptor(udev);
-	udev->bos = bos;
+	/* release the new BOS descriptor allocated  by hub_port_init() */
+	if (udev->bos != bos) {
+		usb_release_bos_descriptor(udev);
+		udev->bos = bos;
+	}
 	return 0;
  
 re_enumerate:

-- 
2.7.1