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Commit 8dcc5b0a authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by David S. Miller
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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: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDavid 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;