linux-kernel - Re: [PATCH v2 for-4.5] vfio: fix ioctl error handling

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Date:	Sun, 28 Feb 2016 16:25:07 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Baptiste Reynal <b.reynal@...tualopensystems.com>,
	Antonios Motakis <a.motakis@...tualopensystems.com>,
	Eric Auger <eric.auger@...aro.org>,
	Julia Lawall <Julia.Lawall@...6.fr>, kvm@...r.kernel.org
Subject: Re: [PATCH v2 for-4.5] vfio: fix ioctl error handling

On Sun, Feb 28, 2016 at 08:23:36AM -0600, Alex Williamson wrote:
> On Sun, 28 Feb 2016 15:51:49 +0200
> "Michael S. Tsirkin" <mst@...hat.com> wrote:
> 
> > Calling return copy_to_user(...) in an ioctl will not
> > do the right thing if there's a pagefault:
> > copy_to_user returns the number of bytes not copied
> > in this case.
> > 
> > Fix up vfio to do
> > 	if (copy_to_user(...))
> > 		return -EFAULT;
> > 	return 0;
> > 
> > everywhere.
> > 
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> > 
> > Changes from v1:
> > 	fix up good path logic to return 0.
> > 
> > Compiled only.
> > 
> >  drivers/vfio/pci/vfio_pci.c                  | 12 +++++++++---
> >  drivers/vfio/platform/vfio_platform_common.c | 12 +++++++++---
> >  drivers/vfio/vfio_iommu_type1.c              |  8 ++++++--
> >  3 files changed, 24 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index 2760a7b..286b91f 100644
> > --- a/drivers/vfio/pci/vfio_pci.c
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -446,7 +446,9 @@ static long vfio_pci_ioctl(void *device_data,
> >  		info.num_regions = VFIO_PCI_NUM_REGIONS;
> >  		info.num_irqs = VFIO_PCI_NUM_IRQS;
> >  
> > -		return copy_to_user((void __user *)arg, &info, minsz);
> > +		if (copy_to_user((void __user *)arg, &info, minsz))
> > +			return -EFAULT;
> > +		return 0;
> 
> Any objection to a ternary in each case?
> 
> 		return copy_to_user((void __user *)arg,
> 				    &info, minsz) ? -EFAULT : 0;

If you prefer, I'll do it in v3.