linux-kernel - Re: [linux-usb-devel] 2.6.20-rc4: null pointer deref in khubd

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Date:	Wed, 10 Jan 2007 17:35:21 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	linux-usb-devel@...ts.sourceforge.net,
	Andrew Morton <akpm@...l.org>, Greg KH <greg@...ah.com>,
	Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [linux-usb-devel] 2.6.20-rc4: null pointer deref in khubd

On Wed, 10 Jan 2007, Oliver Neukum wrote:

> Am Mittwoch, 10. Januar 2007 18:31 schrieb Alan Stern:
> > > Regarding the bug this device uncovers, it seems to me that this in drivers/base/core.c
> > >       if (parent)
> > >               klist_add_tail(&dev->knode_parent, &parent->klist_children);
> > > should make knode_parent a valid node under all circumstances.
> > > Hm.
> > 
> > I haven't seen the original bug report.  Where does the NULL pointer deref 
> > occur?
> 
> Apparently here: drivers/base/core.c:
> 
> void device_del(struct device * dev)
> {
> 	struct device * parent = dev->parent;
> 	struct class_interface *class_intf;
> 
> 	if (parent)
> 		klist_del(&dev->knode_parent);
> 
> The obvious change with this device is that usb_set_configuration() is never
> called, but that should not matter.

No, I think you're barking up the wrong tree.

Pavel, did you have CONFIG_USB_MULTITHREAD_PROBE turned on?  I bet you did 
-- there's no other way to generate the messages in your syslog.

Don't use that kconfig option.  It's broken (as you saw) and needs to be
either removed or replaced.

Alan Stern

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