Re: NULL pointer dereference in veth_stats_one

Ben Hutchings
2013-01-04T18:17:27Z

On Fri, 2013-01-04 at 08:17 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> On Fri, 2013-01-04 at 07:45 -0800, Eric Dumazet wrote:
> > On Fri, 2013-01-04 at 10:59 +0000, Tom Parkin wrote:
> > > Hi list,
> > >
> > > I recently tripped over a NULL pointer dereference in the veth driver.
> > > I'm running a 3.8.0_rc1 (updated from net-next git tree this morning)
> > > on an Athlon 64 X2 machine running a 32 bit kernel. To trigger the
> > > oops I simply created a veth interface as follows:
> > >
> > > ip link add name ve0 type veth peer name ve1
> > >
> > > I did a little digging in the git history and I note that veth
> > > statistics changed a little with commit 2681128f0ced8aa4. I tried
> > > reverting that commit in my tree, which made the oops go away again.
> > >
> > > Thanks,
> > > Tom
> >
> > Thanks Tom, I'll fix this.
> >
>
> Oh well, a last minute change again...
>
> I was fooled by veth_get_ethtool_stats() doing the priv->peer->ifindex
> deref without checking.
[...]
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -162,15 +162,18 @@ static struct rtnl_link_stats64 *veth_get_stats64(struct net_device *dev,
> struct rtnl_link_stats64 *tot)
> {
> struct veth_priv *priv = netdev_priv(dev);
> + struct net_device *peer = priv->peer;
> struct pcpu_vstats one;
>
> tot->tx_dropped = veth_stats_one(&one, dev);
> tot->tx_bytes = one.bytes;
> tot->tx_packets = one.packets;
>
> - tot->rx_dropped = veth_stats_one(&one, priv->peer);
> - tot->rx_bytes = one.bytes;
> - tot->rx_packets = one.packets;
> + if (peer) {

This possibly needs some memory barriers to properly synchronise with
veth_newlink(). But can you not move initialisation of the peer
pointers before registration of the devices in veth_newlink(), so that
veth_get_stats64() cannot be called before they are initialised?

Ben.

> + tot->rx_dropped = veth_stats_one(&one, peer);
> + tot->rx_bytes = one.bytes;
> + tot->rx_packets = one.packets;
> + }
>
> return tot;
> }

--
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.