patch "USB: fix invalid memory access in hub_activate()" added to usb-linus

This is a note to let you know that I've just added the patch titled

USB: fix invalid memory access in hub_activate()

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Alan Stern <[email protected]>
Date: Wed, 16 Dec 2015 13:32:38 -0500
Subject: USB: fix invalid memory access in hub_activate()

Commit 8520f38099cc ("USB: change hub initialization sleeps to delayed_work") changed the hub_activate() routine to make part of it run in a workqueue. However, the commit failed to take a reference to the usb_hub structure or to lock the hub interface while doing so. As a result, if a hub is plugged in and quickly unplugged before the work routine can run, the routine will try to access memory that has been deallocated. Or, if the hub is unplugged while the routine is running, the memory may be deallocated while it is in active use.

This patch fixes the problem by taking a reference to the usb_hub at the start of hub_activate() and releasing it at the end (when the work is finished), and by locking the hub interface while the work routine is running. It also adds a check at the start of the routine to see if the hub has already been disconnected, in which nothing should be done.

---
 drivers/usb/core/hub.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

index a5cc032ef77a..ddbf32d599cb 100644
@@ -1035,10 +1035,20 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 	unsigned delay;
 
 	/* Continue a partial initialization */
-	if (type == HUB_INIT2)
-		goto init2;
-	if (type == HUB_INIT3)
+	if (type == HUB_INIT2 || type == HUB_INIT3) {
+		device_lock(hub->intfdev);
+
+		/* Was the hub disconnected while we were waiting? */
+		if (hub->disconnected) {
+			device_unlock(hub->intfdev);
+			kref_put(&hub->kref, hub_release);
+			return;
+		}
+		if (type == HUB_INIT2)
+			goto init2;
 		goto init3;
+	}
+	kref_get(&hub->kref);
 
 	/* The superspeed hub except for root hub has to use Hub Depth
 	 * value as an offset into the route string to locate the bits

@@ -1236,6 +1246,7 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 			queue_delayed_work(system_power_efficient_wq,
 					&hub->init_work,
 					msecs_to_jiffies(delay));
+			device_unlock(hub->intfdev);
 			return;		/* Continues at init3: below */
 		} else {
 			msleep(delay);

@@ -1257,6 +1268,11 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 	/* Allow autosuspend if it was suppressed */
 	if (type <= HUB_INIT3)
 		usb_autopm_put_interface_async(to_usb_interface(hub->intfdev));
+
+	if (type == HUB_INIT2 || type == HUB_INIT3)
+		device_unlock(hub->intfdev);
+
+	kref_put(&hub->kref, hub_release);
 }
 
 /* Implement the continuations for the delays above */

2.6.4