Re: [PATCH] vhost-net: fix range checking in mrg bufs case

[Jason Wang]

Tested-by: Jason Wang <jasowang@xxxxxxxxxx>

----- "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:

> In mergeable buffer case, we use headcount, log_num
> and seg as indexes in same-size arrays, and
> we know that headcount <= seg and
> log_num equals either 0 or seg.
> 
> Therefore, the right thing to do is range-check seg,
> not headcount as we do now: these will be different
> if guest chains s/g descriptors (this does not
> happen now, but we can not trust the guest).
> 
> Long term, we should add BUG_ON checks to verify
> two other indexes are what we think they should be.
> 
> Reported-by: Jason Wang <jasowang@xxxxxxxxxx>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> 
> Dave, I'll queue this on my tree, no need to bother.
> 
>  drivers/vhost/net.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 6400cd5..f095de6 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -245,7 +245,7 @@ static int get_rx_bufs(struct vhost_virtqueue
> *vq,
>  	int r, nlogs = 0;
>  
>  	while (datalen > 0) {
> -		if (unlikely(headcount >= VHOST_NET_MAX_SG)) {
> +		if (unlikely(seg >= VHOST_NET_MAX_SG)) {
>  			r = -ENOBUFS;
>  			goto err;
>  		}
> -- 
> 1.7.3.rc1.5.ge5969
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