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

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Message-ID: <20160228082336.721d97f8@ul30vt.home>
Date:	Sun, 28 Feb 2016 08:23:36 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	"Michael S. Tsirkin" <mst@...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, 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;