Re: [PATCH net] vhost: fix OOB in get_rx_bufs()

[David Miller]

From: Jason Wang <jasowang@xxxxxxxxxx>
Date: Mon, 28 Jan 2019 15:05:05 +0800

> After batched used ring updating was introduced in commit e2b3b35eb989
> ("vhost_net: batch used ring update in rx"). We tend to batch heads in
> vq->heads for more than one packet. But the quota passed to
> get_rx_bufs() was not correctly limited, which can result a OOB write
> in vq->heads.
> 
>         headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx,
>                     vhost_len, &in, vq_log, &log,
>                     likely(mergeable) ? UIO_MAXIOV : 1);
> 
> UIO_MAXIOV was still used which is wrong since we could have batched
> used in vq->heads, this will cause OOB if the next buffer needs more
> than 960 (1024 (UIO_MAXIOV) - 64 (VHOST_NET_BATCH)) heads after we've
> batched 64 (VHOST_NET_BATCH) heads:
 ...
> Fixing this by allocating UIO_MAXIOV + VHOST_NET_BATCH iovs for
> vhost-net. This is done through set the limitation through
> vhost_dev_init(), then set_owner can allocate the number of iov in a
> per device manner.
> 
> This fixes CVE-2018-16880.
> 
> Fixes: e2b3b35eb989 ("vhost_net: batch used ring update in rx")
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>

Applied and queued up for -stable, thanks!