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 <bro...@redhat.com>
---
drivers/net/virtio_net.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 1e0e0fce3ab2..9bb9e562b893 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -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;
