1// SPDX-License-Identifier: GPL-2.0
  2/* Copyright (c) 2017-18 David Ahern <dsahern@gmail.com>
  3 *
  4 * This program is free software; you can redistribute it and/or
  5 * modify it under the terms of version 2 of the GNU General Public
  6 * License as published by the Free Software Foundation.
  7 *
  8 * This program is distributed in the hope that it will be useful, but
  9 * WITHOUT ANY WARRANTY; without even the implied warranty of
 10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 11 * General Public License for more details.
 12 */
 13#define KBUILD_MODNAME "foo"
 14#include <uapi/linux/bpf.h>
 15#include <linux/in.h>
 16#include <linux/if_ether.h>
 17#include <linux/if_packet.h>
 18#include <linux/if_vlan.h>
 19#include <linux/ip.h>
 20#include <linux/ipv6.h>
 21
 22#include "bpf_helpers.h"
 23
 24#define IPV6_FLOWINFO_MASK              cpu_to_be32(0x0FFFFFFF)
 25
 26/* For TX-traffic redirect requires net_device ifindex to be in this devmap */
 27struct bpf_map_def SEC("maps") xdp_tx_ports = {
 28	.type = BPF_MAP_TYPE_DEVMAP,
 29	.key_size = sizeof(int),
 30	.value_size = sizeof(int),
 31	.max_entries = 64,
 32};
 33
 34/* from include/net/ip.h */
 35static __always_inline int ip_decrease_ttl(struct iphdr *iph)
 36{
 37	u32 check = (__force u32)iph->check;
 38
 39	check += (__force u32)htons(0x0100);
 40	iph->check = (__force __sum16)(check + (check >= 0xFFFF));
 41	return --iph->ttl;
 42}
 43
 44static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
 45{
 46	void *data_end = (void *)(long)ctx->data_end;
 47	void *data = (void *)(long)ctx->data;
 48	struct bpf_fib_lookup fib_params;
 49	struct ethhdr *eth = data;
 50	struct ipv6hdr *ip6h;
 51	struct iphdr *iph;
 52	u16 h_proto;
 53	u64 nh_off;
 54	int rc;
 55
 56	nh_off = sizeof(*eth);
 57	if (data + nh_off > data_end)
 58		return XDP_DROP;
 59
 60	__builtin_memset(&fib_params, 0, sizeof(fib_params));
 61
 62	h_proto = eth->h_proto;
 63	if (h_proto == htons(ETH_P_IP)) {
 64		iph = data + nh_off;
 65
 66		if (iph + 1 > data_end)
 67			return XDP_DROP;
 68
 69		if (iph->ttl <= 1)
 70			return XDP_PASS;
 71
 72		fib_params.family	= AF_INET;
 73		fib_params.tos		= iph->tos;
 74		fib_params.l4_protocol	= iph->protocol;
 75		fib_params.sport	= 0;
 76		fib_params.dport	= 0;
 77		fib_params.tot_len	= ntohs(iph->tot_len);
 78		fib_params.ipv4_src	= iph->saddr;
 79		fib_params.ipv4_dst	= iph->daddr;
 80	} else if (h_proto == htons(ETH_P_IPV6)) {
 81		struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;
 82		struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst;
 83
 84		ip6h = data + nh_off;
 85		if (ip6h + 1 > data_end)
 86			return XDP_DROP;
 87
 88		if (ip6h->hop_limit <= 1)
 89			return XDP_PASS;
 90
 91		fib_params.family	= AF_INET6;
 92		fib_params.flowinfo	= *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;
 93		fib_params.l4_protocol	= ip6h->nexthdr;
 94		fib_params.sport	= 0;
 95		fib_params.dport	= 0;
 96		fib_params.tot_len	= ntohs(ip6h->payload_len);
 97		*src			= ip6h->saddr;
 98		*dst			= ip6h->daddr;
 99	} else {
100		return XDP_PASS;
101	}
102
103	fib_params.ifindex = ctx->ingress_ifindex;
104
105	rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
106	/*
107	 * Some rc (return codes) from bpf_fib_lookup() are important,
108	 * to understand how this XDP-prog interacts with network stack.
109	 *
110	 * BPF_FIB_LKUP_RET_NO_NEIGH:
111	 *  Even if route lookup was a success, then the MAC-addresses are also
112	 *  needed.  This is obtained from arp/neighbour table, but if table is
113	 *  (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned.  To avoid
114	 *  doing ARP lookup directly from XDP, then send packet to normal
115	 *  network stack via XDP_PASS and expect it will do ARP resolution.
116	 *
117	 * BPF_FIB_LKUP_RET_FWD_DISABLED:
118	 *  The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding
119	 *  setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not
120	 *  enabled this on ingress device.
121	 */
122	if (rc == BPF_FIB_LKUP_RET_SUCCESS) {
123		/* Verify egress index has been configured as TX-port.
124		 * (Note: User can still have inserted an egress ifindex that
125		 * doesn't support XDP xmit, which will result in packet drops).
126		 *
127		 * Note: lookup in devmap supported since 0cdbb4b09a0.
128		 * If not supported will fail with:
129		 *  cannot pass map_type 14 into func bpf_map_lookup_elem#1:
130		 */
131		if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex))
132			return XDP_PASS;
133
134		if (h_proto == htons(ETH_P_IP))
135			ip_decrease_ttl(iph);
136		else if (h_proto == htons(ETH_P_IPV6))
137			ip6h->hop_limit--;
138
139		memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
140		memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
141		return bpf_redirect_map(&xdp_tx_ports, fib_params.ifindex, 0);
142	}
143
144	return XDP_PASS;
145}
146
147SEC("xdp_fwd")
148int xdp_fwd_prog(struct xdp_md *ctx)
149{
150	return xdp_fwd_flags(ctx, 0);
151}
152
153SEC("xdp_fwd_direct")
154int xdp_fwd_direct_prog(struct xdp_md *ctx)
155{
156	return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);
157}
158
159char _license[] SEC("license") = "GPL";