linux-kernel - RE: [PATCH] usb/core: fix NULL pointer dereference in recursively_mark

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Date:	Thu, 2 Jan 2014 14:22:19 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Du, ChangbinX" <changbinx.du@...el.com>
cc:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"sarah.a.sharp@...ux.intel.com" <sarah.a.sharp@...ux.intel.com>,
	"Lan, Tianyu" <tianyu.lan@...el.com>,
	"burzalodowa@...il.com" <burzalodowa@...il.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb/core: fix NULL pointer dereference in
 recursively_mark_NOTATTACHED

On Thu, 26 Dec 2013, Du, ChangbinX wrote:

> I can reproduce issue by adding a delay just after usb_set_intfdata(intf, NULL)
>  (echo -1 > bConfigurationValue to trigger hub_dissconnect())without your patch.
> 
> After patch applied, cannot reproduce and didn't found any other issue. Patch works well.
> 
> Alan, need I update patch to v2 or you will do it?

Changbin, after looking more closely I realized there was a second 
aspect to this race: recursively_mark_NOTATTACHED uses hub->ports[i] 
while hub_disconnect removes the port devices.  You ought to be 
able to cause an oops by inserting a delay just after the loop where 
usb_hub_remove_port_device is called.

The updated patch below should fix both problems.  Can you test it?

Alan Stern



Index: usb-3.13/drivers/usb/core/hub.c
===================================================================
--- usb-3.13.orig/drivers/usb/core/hub.c
+++ usb-3.13/drivers/usb/core/hub.c
@@ -1607,7 +1607,7 @@ static void hub_disconnect(struct usb_in
 {
 	struct usb_hub *hub = usb_get_intfdata(intf);
 	struct usb_device *hdev = interface_to_usbdev(intf);
-	int i;
+	int port1;
 
 	/* Take the hub off the event list and don't let it be added again */
 	spin_lock_irq(&hub_event_lock);
@@ -1622,11 +1622,15 @@ static void hub_disconnect(struct usb_in
 	hub->error = 0;
 	hub_quiesce(hub, HUB_DISCONNECT);
 
-	usb_set_intfdata (intf, NULL);
+	/* Avoid races with recursively_mark_NOTATTACHED() */
+	spin_lock_irq(&device_state_lock);
+	port1 = hdev->maxchild;
+	hdev->maxchild = 0;
+	usb_set_intfdata(intf, NULL);
+	spin_unlock_irq(&device_state_lock);
 
-	for (i = 0; i < hdev->maxchild; i++)
-		usb_hub_remove_port_device(hub, i + 1);
-	hub->hdev->maxchild = 0;
+	for (; port1 > 0; --port1)
+		usb_hub_remove_port_device(hub, port1);
 
 	if (hub->hdev->speed == USB_SPEED_HIGH)
 		highspeed_hubs--;

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