From 8dcc5b0ab0ec9a2efb3362d380272546b8b2ee26 Mon Sep 17 00:00:00 2001 From: Jesper Dangaard Brouer Date: Tue, 20 Feb 2018 14:32:20 +0100 Subject: [PATCH] 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: 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 Acked-by: John Fastabend Signed-off-by: David S. Miller --- 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;