netdev - Re: [PATCH net] vhost: fix OOB in get_rx

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Date:   Tue, 29 Jan 2019 15:10:26 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     mst@...hat.com
Cc:     jasowang@...hat.com, stefanha@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] vhost: fix OOB in get_rx_bufs()

From: "Michael S. Tsirkin" <mst@...hat.com>
Date: Tue, 29 Jan 2019 17:54:44 -0500

> On Mon, Jan 28, 2019 at 10:54:44PM -0800, David Miller wrote:
>> From: Jason Wang <jasowang@...hat.com>
>> 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@...hat.com>
>> 
>> Applied and queued up for -stable, thanks!
> 
> Wow it seems we are down to hours round time post to queue.
> It would be hard to keep up that rate generally.
> However, I am guessing this was already in downstreams, and it's a CVE,
> so I guess it's a no brainer and review wasn't really necessary - was
> that the idea? Just checking.

Yeah the CVE pushed my hand a little bit, and I knew I was going to send Linus
a pull request today because David Watson needs some TLS changes in net-next.