linux-kernel - Re: [PATCH] vfio: fix vfio_info_cap

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Date:   Mon, 21 Nov 2016 13:37:45 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH] vfio: fix vfio_info_cap_add/shift

On Mon, 21 Nov 2016 07:21:02 +0100
Eric Auger <eric.auger@...hat.com> wrote:

> Capability header next field is an offset relative to the start of
> the INFO buffer. tmp->next is assigned the proper value but iterations
> implemented in vfio_info_cap_add and vfio_info_cap_shift use next
> as an offset between the headers. When coping with multiple capabilities
> this leads to an Oops.
> 
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> ---
>  drivers/vfio/vfio.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index d1d70e0..1e838d1 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1763,7 +1763,7 @@ struct vfio_info_cap_header *vfio_info_cap_add(struct vfio_info_cap *caps,
>  	header->version = version;
>  
>  	/* Add to the end of the capability chain */
> -	for (tmp = caps->buf; tmp->next; tmp = (void *)tmp + tmp->next)
> +	for (tmp = buf; tmp->next; tmp = buf + tmp->next)
>  		; /* nothing */
>  
>  	tmp->next = caps->size;
> @@ -1776,8 +1776,9 @@ EXPORT_SYMBOL_GPL(vfio_info_cap_add);
>  void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset)
>  {
>  	struct vfio_info_cap_header *tmp;
> +	void *buf = (void *)caps->buf;
>  
> -	for (tmp = caps->buf; tmp->next; tmp = (void *)tmp + tmp->next - offset)
> +	for (tmp = buf; tmp->next; tmp = buf + tmp->next - offset)
>  		tmp->next += offset;
>  }
>  EXPORT_SYMBOL_GPL(vfio_info_cap_shift);

Thanks, good to get this fixed before we start getting multiple entries
in the chain and expose it via mdev.  For that same reason I also don't
see that this needs any sort of stable backport as the existing code
works for the single entries in the tree.  Applied to next branch for
4.10 with David's R-b.  Thanks,

Alex