linux-kernel - Re: [patch] drivers: Fix bogus 0 error return in device

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Date:	Thu, 10 Dec 2009 22:55:14 +0100
From:	"Hans J. Koch" <hjk@...utronix.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Greg KH <gregkh@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [patch] drivers: Fix bogus 0 error return in device_add()

On Thu, Dec 10, 2009 at 10:01:10PM +0100, Thomas Gleixner wrote:
> On Thu, 10 Dec 2009, Greg KH wrote:
> > On Thu, Dec 10, 2009 at 07:32:49PM -0000, Thomas Gleixner wrote:
> > > If device_add() is called with a device which does not have dev->p set
> > > up, then device_private_init() is called. If that succeeds, then the
> > > error variable is set to 0. Now if the dev_name(dev) check further
> > > down fails, then device_add() correctly terminates, but returns 0.
> > > That of course lets the driver progress. If later another driver uses
> > > this half set up device as parent then device_add() of the child
> > > device explodes and renders sysfs completely unusable.
> > > 
> > > Set the error to -EINVAL if dev_name() check fails.
> > 
> > That's a good catch, thanks.
> > 
> > Is anything currently triggering this?  Or did you just find it by
> > reading the code?
> 
> Hans-Juergen had a buggy vendor driver where init_name was not
> initialized. So the driver probing succeeded and after that a
> depending driver crashed somewhere in device_add().

That was one of these USB UDC drivers. It falsely reported OK at probe time
and crashed when modprobing a gadget driver. Complete hang of the machine
could be achieved by just doing "ls /sys"...
Of course, it's the driver's fault not to set init_name, but it's a bit
annoying if such mistakes freeze your machine instead of simply producing
an error that helps fixing the driver.

Thanks,
Hans

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