linux-kernel - Re: [PATCH] vfio/type1: Fix unmap overflow off-by-one

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Date:   Wed, 9 Jan 2019 11:11:03 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        dan.carpenter@...cle.com, cohuck@...hat.com
Subject: Re: [PATCH] vfio/type1: Fix unmap overflow off-by-one

On Tue, Jan 08, 2019 at 09:40:06AM -0700, Alex Williamson wrote:
> The below referenced commit adds a test for integer overflow, but in
> doing so prevents the unmap ioctl from ever including the last page of
> the address space.  Subtract one to compare to the last address of the
> unmap to avoid the overflow and wrap-around.
> 
> Fixes: 71a7d3d78e3c ("vfio/type1: silence integer overflow warning")
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1662291
> Cc: Dan Carpenter <dan.carpenter@...cle.com>
> Reported-by: Pei Zhang <pezhang@...hat.com>
> Debugged-by: Peter Xu <peterx@...hat.com>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>

I tested this against the QEMU reboot error and it works.

Reviewed-by: Peter Xu <peterx@...hat.com>
Tested-by: Peter Xu <peterx@...hat.com>

Thanks,

> ---
>  drivers/vfio/vfio_iommu_type1.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 7651cfb14836..73652e21efec 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -878,7 +878,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>  		return -EINVAL;
>  	if (!unmap->size || unmap->size & mask)
>  		return -EINVAL;
> -	if (unmap->iova + unmap->size < unmap->iova ||
> +	if (unmap->iova + unmap->size - 1 < unmap->iova ||
>  	    unmap->size > SIZE_MAX)
>  		return -EINVAL;
>  
> 

-- 
Peter Xu