[3.19.y-ckt stable] Patch "USB: fix invalid memory access in hub_activate()" has been added to the 3.19.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    USB: fix invalid memory access in hub_activate()

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt13.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 509fe05c270d33f2d52b0c5bb9d59212e9b9c5c0 Mon Sep 17 00:00:00 2001
From: Alan Stern <stern at rowland.harvard.edu>
Date: Wed, 16 Dec 2015 13:32:38 -0500
Subject: USB: fix invalid memory access in hub_activate()

commit e50293ef9775c5f1cf3fcc093037dd6a8c5684ea upstream.

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.

Signed-off-by: Alan Stern <stern at rowland.harvard.edu>
Reported-by: Alexandru Cornea <alexandru.cornea at intel.com>
Tested-by: Alexandru Cornea <alexandru.cornea at intel.com>
Fixes: 8520f38099cc ("USB: change hub initialization sleeps to delayed_work")
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/usb/core/hub.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 5f719cb..fde1e10 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1034,10 +1034,20 @@ 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
@@ -1235,6 +1245,7 @@ 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);
@@ -1256,6 +1267,11 @@ 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 */
--
1.9.1