Re: [PATCH 2/2] usb: fail on usb_hub_create_port_device() errors

[Krzysztof Mazur <krzysiek@podlesie.net>]

On Tue, Aug 20, 2013 at 03:50:37PM -0400, Alan Stern wrote:
> On Tue, 20 Aug 2013, Krzysztof Mazur wrote:
> 
> > On Tue, Aug 20, 2013 at 02:18:57PM -0400, Alan Stern wrote:
> > > On Tue, 20 Aug 2013, Krzysztof Mazur wrote:
> > > 
> > > > Ignoring usb_hub_create_port_device() errors cause later NULL pointer
> > > > deference when uninitialized hub->ports[i] entries are dereferenced
> > > > after port memory allocation error.
> > > > 
> > > > Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net>
> > > > ---
> > > > I'm not sure if failing in that case is a good idea, but other solutions
> > > > are more complex.
> > > > 
> > > > I tried also changing hdev->maxchild and skiping initialization
> > > > of later ports, but it didn't work because in some cases
> > > > hub->descriptor->bNbrPorts is used instead of hdev->maxchild.
> > > > With simulated usb_hub_create_port_device() failure I have an Oops
> > > > in hub_power_on().
> > > 
> > > I think this patch is correct.  However, we also should change the 
> > > other places that refer to bNbrPorts; make them use maxchild instead.
> > 
> > Ok, I can try to catch all such cases and fix problems with
> > maxchild < bNBrPorts, but I think that changing bNBrPorts to maxchild
> > might be not enough. For instance:
> 
> We should never have maxchild < bNbrPorts (unless maxchild is 0).  But 
> just in case we do, changing the code is a good idea.
> 
> Besides, "hub->maxchild" is shorter and easier to read than
> "hub->descriptor->bNbrPorts".  :-)
> 

It's "hub->hdev->maxchild", but it's still shorter and
in many places it's just "hdev->maxchild" :)

I tested that with maxchild < bNbrPorts and there are no NULL pointer
dereferences anymore.

Krzysiek
-- >8 --
Subject: [PATCH 3/2] usb: don't use bNbrPorts after initialization

After successful initialization hub->descriptor->bNbrPorts and
hub->hdev->maxchild are equal, but using hub->hdev->maxchild is
preferred because that value is explicitly used for initialization
of hub->ports[].

Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net>
---
 drivers/usb/core/hub.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 292ffa8..86e353f 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -451,7 +451,7 @@ static void led_work (struct work_struct *work)
 	if (hdev->state != USB_STATE_CONFIGURED || hub->quiescing)
 		return;
 
-	for (i = 0; i < hub->descriptor->bNbrPorts; i++) {
+	for (i = 0; i < hdev->maxchild; i++) {
 		unsigned	selector, mode;
 
 		/* 30%-50% duty cycle */
@@ -500,7 +500,7 @@ static void led_work (struct work_struct *work)
 	}
 	if (!changed && blinkenlights) {
 		cursor++;
-		cursor %= hub->descriptor->bNbrPorts;
+		cursor %= hdev->maxchild;
 		set_port_led(hub, cursor + 1, HUB_LED_GREEN);
 		hub->indicator[cursor] = INDICATOR_CYCLE;
 		changed++;
@@ -826,7 +826,7 @@ static unsigned hub_power_on(struct usb_hub *hub, bool do_delay)
 	else
 		dev_dbg(hub->intfdev, "trying to enable port power on "
 				"non-switchable hub\n");
-	for (port1 = 1; port1 <= hub->descriptor->bNbrPorts; port1++)
+	for (port1 = 1; port1 <= hub->hdev->maxchild; port1++)
 		if (hub->ports[port1 - 1]->power_is_on)
 			set_port_feature(hub->hdev, port1, USB_PORT_FEAT_POWER);
 		else
@@ -4655,9 +4655,7 @@ static void hub_events(void)
 		hub_dev = hub->intfdev;
 		intf = to_usb_interface(hub_dev);
 		dev_dbg(hub_dev, "state %d ports %d chg %04x evt %04x\n",
-				hdev->state, hub->descriptor
-					? hub->descriptor->bNbrPorts
-					: 0,
+				hdev->state, hdev->maxchild,
 				/* NOTE: expects max 15 ports... */
 				(u16) hub->change_bits[0],
 				(u16) hub->event_bits[0]);
@@ -4702,7 +4700,7 @@ static void hub_events(void)
 		}
 
 		/* deal with port status changes */
-		for (i = 1; i <= hub->descriptor->bNbrPorts; i++) {
+		for (i = 1; i <= hdev->maxchild; i++) {
 			if (test_bit(i, hub->busy_bits))
 				continue;
 			connect_change = test_bit(i, hub->change_bits);
-- 
1.8.4.rc4.527.g303b16c