Commit 8dcc5b0a authored Feb 20, 2018 by Jesper Dangaard Brouer Committed by David S. Miller Feb 21, 2018

virtio_net: fix ndo_xdp_xmit crash towards dev not ready for XDP



When a driver implements the ndo_xdp_xmit() function, there is
(currently) no generic way to determine whether it is safe to call.

It is e.g. unsafe to call the drivers ndo_xdp_xmit, if it have not
allocated the needed XDP TX queues yet.  This is the case for
virtio_net, which first allocates the XDP TX queues once an XDP/bpf
prog is attached (in virtnet_xdp_set()).

Thus, a crash will occur for virtio_net when redirecting to another
virtio_net device's ndo_xdp_xmit, which have not attached a XDP prog.
The sample xdp_redirect_map tries to attach a dummy XDP prog to take
this into account, but it can also easily fail if the virtio_net (or
actually underlying vhost driver) have not allocated enough extra
queues for the device.

Allocating more queue this is currently a manual config.
Hint for libvirt XML add:

  <driver name='vhost' queues='16'>
    <host mrg_rxbuf='off'/>
    <guest tso4='off' tso6='off' ecn='off' ufo='off'/>
  </driver>

The solution in this patch is to check that the device have loaded an
XDP/bpf prog before proceeding.  This is similar to the check
performed in driver ixgbe.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 11b7d897

drivers/net/virtio_net.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -452,8 +452,18 @@ static bool __virtnet_xdp_xmit(struct virtnet_info *vi,
		static int virtnet_xdp_xmit(struct net_device dev, struct xdp_buff xdp)
		{
		struct virtnet_info *vi = netdev_priv(dev);
		bool sent = __virtnet_xdp_xmit(vi, xdp);
		struct receive_queue *rq = vi->rq;
		struct bpf_prog *xdp_prog;
		bool sent;

		/* Only allow ndo_xdp_xmit if XDP is loaded on dev, as this
		* indicate XDP resources have been successfully allocated.
		*/
		xdp_prog = rcu_dereference(rq->xdp_prog);
		if (!xdp_prog)
		return -ENXIO;

		sent = __virtnet_xdp_xmit(vi, xdp);
		if (!sent)
		return -ENOSPC;
		return 0;

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