linux-kernel - Re: Flaws with "UIO: Add the User IO core code" (with patch)

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Message-Id: <200704282052.45489.hjk@linutronix.de>
Date:	Sat, 28 Apr 2007 20:52:45 +0200
From:	Hans-Jürgen Koch <hjk@...utronix.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	torvalds@...l.org, Thomas Gleixner <tglx@...utronix.de>,
	Benedikt Spranger <b.spranger@...utronix.de>
Subject: Re: Flaws with "UIO: Add the User IO core code" (with patch)

Am Samstag 28 April 2007 01:19 schrieb Alan Cox:
> > +static ssize_t uio_read(struct file *filep, char __user *buf,
> > +			size_t count, loff_t *ppos)
> > +{
> > +	struct uio_listener *listener = filep->private_data;
> > +	struct uio_device *idev = listener->dev;
> > +	DECLARE_WAITQUEUE(wait, current);
> > +	ssize_t retval;
> > +	int event_count;
> > +
> > +	if (idev->info->irq == UIO_IRQ_NONE)
> > +		return -EIO;
> > +
> > +	if (count != sizeof(int))
> > +		return -EINVAL;
> 
> AFAIK we don't currently have any platform that runs binaries with
> different sizes of "int" but this is a) an unsigned value anyway, and b)
> should be a fixed type (eg u32)

I reviewed the code once more and find it OK. There is only one legal
value for the parameter "count" of uio_read(), and that's sizeof(int).
The data that is actually read is the element "event" of struct uio_device,
which is of type atomic_t. The latter has the size of an int.

Unfortunately, the fact that the read count _must_ be sizeof(int) is not
mentioned in the documentation. I'll send a patch for that ASAP.

> 
> Otherwise it looks ok at the momenmt, although there is a real nasty
> waiting for anyone who tries to use it. At the point open is possible or
> IRQs can be enabled you are safe in the core merged as idev->info is
> always valid, but any driver module trying to go back via info->uio_dev
> has a NULL pointer for an early IRQ or open event.

This patch should fix it:


Index: linux-2.6.22-rc/drivers/uio/uio.c
===================================================================
--- linux-2.6.22-rc.orig/drivers/uio/uio.c	2007-04-28 20:01:02.000000000 +0200
+++ linux-2.6.22-rc/drivers/uio/uio.c	2007-04-28 20:15:00.000000000 +0200
@@ -633,6 +633,8 @@
 	if (ret)
 		goto err_uio_dev_add_attributes;
 
+	info->uio_dev = idev;
+
 	if (idev->info->irq >= 0) {
 		ret = request_irq(idev->info->irq, uio_interrupt,
 				  idev->info->irq_flags, idev->info->name, idev);
@@ -640,7 +642,6 @@
 			goto err_request_irq;
 	}
 
-	info->uio_dev = idev;
 	return 0;
 
 err_request_irq:


Thanks for your review,
Hans

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