xdp: add bpf_redirect helper function

This adds support for a bpf_redirect helper function to the XDP
infrastructure. For now this only supports redirecting to the egress
path of a port.

In order to support drivers handling a xdp_buff natively this patches
uses a new ndo operation ndo_xdp_xmit() that takes pushes a xdp_buff
to the specified device.

If the program specifies either (a) an unknown device or (b) a device
that does not support the operation a BPF warning is thrown and the
XDP_ABORTED error code is returned.

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

1 files changed, 52 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index c7f737058d89..d606a66d1040 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2412,6 +2412,51 @@ static const struct bpf_func_proto bpf_xdp_adjust_head_proto = {
 	.arg2_type	= ARG_ANYTHING,
 };
 
+static int __bpf_tx_xdp(struct net_device *dev, struct xdp_buff *xdp)
+{
+	if (dev->netdev_ops->ndo_xdp_xmit) {
+		dev->netdev_ops->ndo_xdp_xmit(dev, xdp);
+		return 0;
+	}
+	bpf_warn_invalid_xdp_redirect(dev->ifindex);
+	return -EOPNOTSUPP;
+}
+
+int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp)
+{
+	struct redirect_info *ri = this_cpu_ptr(&redirect_info);
+
+	dev = dev_get_by_index_rcu(dev_net(dev), ri->ifindex);
+	ri->ifindex = 0;
+	if (unlikely(!dev)) {
+		bpf_warn_invalid_xdp_redirect(ri->ifindex);
+		return -EINVAL;
+	}
+
+	return __bpf_tx_xdp(dev, xdp);
+}
+EXPORT_SYMBOL_GPL(xdp_do_redirect);
+
+BPF_CALL_2(bpf_xdp_redirect, u32, ifindex, u64, flags)
+{
+	struct redirect_info *ri = this_cpu_ptr(&redirect_info);
+
+	if (unlikely(flags))
+		return XDP_ABORTED;
+
+	ri->ifindex = ifindex;
+	ri->flags = flags;
+	return XDP_REDIRECT;
+}
+
+static const struct bpf_func_proto bpf_xdp_redirect_proto = {
+	.func           = bpf_xdp_redirect,
+	.gpl_only       = false,
+	.ret_type       = RET_INTEGER,
+	.arg1_type      = ARG_ANYTHING,
+	.arg2_type      = ARG_ANYTHING,
+};
+
 bool bpf_helper_changes_pkt_data(void *func)
 {
 	if (func == bpf_skb_vlan_push ||
@@ -3011,6 +3056,8 @@ xdp_func_proto(enum bpf_func_id func_id)
 		return &bpf_get_smp_processor_id_proto;
 	case BPF_FUNC_xdp_adjust_head:
 		return &bpf_xdp_adjust_head_proto;
+	case BPF_FUNC_redirect:
+		return &bpf_xdp_redirect_proto;
 	default:
 		return bpf_base_func_proto(func_id);
 	}
@@ -3310,6 +3357,11 @@ void bpf_warn_invalid_xdp_action(u32 act)
 }
 EXPORT_SYMBOL_GPL(bpf_warn_invalid_xdp_action);
 
+void bpf_warn_invalid_xdp_redirect(u32 ifindex)
+{
+	WARN_ONCE(1, "Illegal XDP redirect to unsupported device ifindex(%i)\n", ifindex);
+}
+
 static bool __is_valid_sock_ops_access(int off, int size)
 {
 	if (off < 0 || off >= sizeof(struct bpf_sock_ops))