linux-kernel - Re: [PATCH v9 2/2] uio: Fix uio driver to refcount device

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Message-ID: <20150608192507.GA13169@roeck-us.net>
Date:	Mon, 8 Jun 2015 12:25:07 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Brian Russell <brian.russell@...cade.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Brian Russell <brussell@...cade.com>,
	"Hans J. Koch" <hjk@...sjkoch.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 2/2] uio: Fix uio driver to refcount device

On Tue, Mar 24, 2015 at 12:59:22PM +0000, Brian Russell wrote:
> 
> 
> On 23/03/15 20:41, Greg Kroah-Hartman wrote:
> > On Fri, Mar 20, 2015 at 02:54:44PM +0000, Brian Russell wrote:
> >> Protect uio driver from its owner being unplugged while there are open fds.
> >> Embed struct device in struct uio_device, use refcounting on device, free
> >> uio_device on release.
> >> info struct passed in uio_register_device can be freed on unregister, so null
> >> out the field in uio_unregister_device and check accesses.
> > 
> > That's really not protecting anything except heavy-handed problems...
> > 
> > Look at the code:
> > 
> >> @@ -493,7 +499,7 @@ static unsigned int uio_poll(struct file *filep, poll_table *wait)
> >>  	struct uio_listener *listener = filep->private_data;
> >>  	struct uio_device *idev = listener->dev;
> >>  
> >> -	if (!idev->info->irq)
> >> +	if (!idev->info || !idev->info->irq)
> >>  		return -EIO;
> >>  
> > 
> > Great, you checked the irq value, but what if it changes the very next
> > line:
> > 
> >>  	poll_wait(filep, &idev->wait, wait);
> > 
> > Or any other line within this function?  Or any other function that you
> > try to check the value for in the beginning...
> > 
> > This really isn't protecting anything "properly", sorry.  Either we
> > don't care about it (hint, I don't think we really do), or we need to
> > properly lock things and check, and protect, things that way.
> > 
> 
> The checks for irq value are already there. I added the checks for the
> idev->info ptr and deliberately nulled it in uio_unregister_device as
> the caller module may free uio_info after unregistering (dpdk's igb_uio
> does anyway) and then release will be called later when fds are closed.
> 
> So I think I definitely need the check in uio_release. I didn't think
> it hurt to return early from poll/read/write if we know the device
> has been unregistered?
> 

What is the final verdict on this patch ? We are seeing the crash in our
system, and I would like to apply a 'final' patch if possible to get it
fixed.

Thanks,
Guenter
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