linux-kernel - Re: [PATCH] vhost: fix vhost_vq_access

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Date:   Mon, 9 Apr 2018 16:58:19 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Stefan Hajnoczi <stefanha@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, jasowang@...hat.com,
        kvm@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] vhost: fix vhost_vq_access_ok() log check

On Mon, Apr 09, 2018 at 09:10:21PM +0800, Stefan Hajnoczi wrote:
> Commit d65026c6c62e7d9616c8ceb5a53b68bcdc050525 ("vhost: validate log
> when IOTLB is enabled") introduced a regression.  The logic was
> originally:
> 
>   if (vq->iotlb)
>       return 1;
>   return A && B;
> 
> After the patch the short-circuit logic for A was inverted:
> 
>   if (A || vq->iotlb)
>       return A;
>   return B;
> 
> The correct logic is:
> 
>   if (!A || vq->iotlb)
>       return A;
>   return B;
> 
> Reported-by: syzbot+65a84dde0214b0387ccd@...kaller.appspotmail.com
> Cc: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  drivers/vhost/vhost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 5320039671b7..f6af4210679a 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1246,7 +1246,7 @@ int vhost_vq_access_ok(struct vhost_virtqueue *vq)
>  {
>  	int ret = vq_log_access_ok(vq, vq->log_base);
>  
> -	if (ret || vq->iotlb)
> +	if (!ret || vq->iotlb)
>  		return ret;
>  
>  	return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
> -- 
> 2.14.3