linux-kernel - Re: [PATCH] vhost: fix end of range for access

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Date:   Tue, 22 Aug 2017 23:49:37 +0900
From:   Koichiro Den <den@...ipeden.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH] vhost: fix end of range for access_ok

On Mon, 2017-08-21 at 22:45 +0300, Michael S. Tsirkin wrote:
> During access_ok checks, addr increases as we iterate over the data
> structure, thus addr + len - 1 will point beyond the end of region we
> are translating.  Harmless since we then verify that the region covers
> addr, but let's not waste cpu cycles.
> 
> Reported-by: Koichiro Den <den@...ipeden.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> 
> Lightly tested, would appreciate an ack from reporter.
> 
>  drivers/vhost/vhost.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index e4613a3..ecd70e4 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1176,7 +1176,7 @@ static int iotlb_access_ok(struct vhost_virtqueue *vq,
>  {
>  	const struct vhost_umem_node *node;
>  	struct vhost_umem *umem = vq->iotlb;
> -	u64 s = 0, size, orig_addr = addr;
> +	u64 s = 0, size, orig_addr = addr, last = addr + len - 1;
>  
>  	if (vhost_vq_meta_fetch(vq, addr, len, type))
>  		return true;
> @@ -1184,7 +1184,7 @@ static int iotlb_access_ok(struct vhost_virtqueue *vq,
>  	while (len > s) {
>  		node = vhost_umem_interval_tree_iter_first(&umem->umem_tree,
>  							   addr,
> -							   addr + len - 1);
> +							   last);
>  		if (node == NULL || node->start > addr) {
>  			vhost_iotlb_miss(vq, addr, access);
>  			return false;

Michael, Thank you for this one.

Acked-by: Koichiro Den <den@...ipeden.com>