linux-kernel - Re: [patch 1/3 v2] vfio: signedness bug in vfio_config_do

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Date:	Thu, 28 Jun 2012 16:24:29 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org, walter harms <wharms@....de>
Subject: Re: [patch 1/3 v2] vfio: signedness bug in vfio_config_do_rw()

On Thu, 2012-06-28 at 11:07 +0300, Dan Carpenter wrote:
> The "count" variable needs to be signed here because we use it to store
> negative error codes.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
> v2: Just declare count as signed.
> 
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index a4f7321..2e00aa8 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -1419,7 +1419,7 @@ void vfio_config_free(struct vfio_pci_device *vdev)
>  }
>  
>  static ssize_t vfio_config_do_rw(struct vfio_pci_device *vdev, char __user *buf,
> -				 size_t count, loff_t *ppos, bool iswrite)
> +				 ssize_t count, loff_t *ppos, bool iswrite)
>  {
>  	struct pci_dev *pdev = vdev->pdev;
>  	struct perm_bits *perm;

signed doesn't seem right for count since just below this chunk we do:

        if (*ppos < 0 || *ppos + count > pdev->cfg_size)
                return -EFAULT;

So then we have to start testing for negative count.  I've added a
ssize_t variable for return that should clear things up.  Thanks for the
report!

Alex

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