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/bpf_helpers.h>
23
24#define IPV6_FLOWINFO_MASK              cpu_to_be32(0x0FFFFFFF)
25
26struct {
27	__uint(type, BPF_MAP_TYPE_DEVMAP);
28	__uint(key_size, sizeof(int));
29	__uint(value_size, sizeof(int));
30	__uint(max_entries, 64);
31} xdp_tx_ports SEC(".maps");
32
33/* from include/net/ip.h */
34static __always_inline int ip_decrease_ttl(struct iphdr *iph)
35{
36	u32 check = (__force u32)iph->check;
37
38	check += (__force u32)htons(0x0100);
39	iph->check = (__force __sum16)(check + (check >= 0xFFFF));
40	return --iph->ttl;
41}
42
43static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
44{
45	void *data_end = (void *)(long)ctx->data_end;
46	void *data = (void *)(long)ctx->data;
47	struct bpf_fib_lookup fib_params;
48	struct ethhdr *eth = data;
49	struct ipv6hdr *ip6h;
50	struct iphdr *iph;
51	u16 h_proto;
52	u64 nh_off;
53	int rc;
54
55	nh_off = sizeof(*eth);
56	if (data + nh_off > data_end)
57		return XDP_DROP;
58
59	__builtin_memset(&fib_params, 0, sizeof(fib_params));
60
61	h_proto = eth->h_proto;
62	if (h_proto == htons(ETH_P_IP)) {
63		iph = data + nh_off;
64
65		if (iph + 1 > data_end)
66			return XDP_DROP;
67
68		if (iph->ttl <= 1)
69			return XDP_PASS;
70
71		fib_params.family	= AF_INET;
72		fib_params.tos		= iph->tos;
73		fib_params.l4_protocol	= iph->protocol;
74		fib_params.sport	= 0;
75		fib_params.dport	= 0;
76		fib_params.tot_len	= ntohs(iph->tot_len);
77		fib_params.ipv4_src	= iph->saddr;
78		fib_params.ipv4_dst	= iph->daddr;
79	} else if (h_proto == htons(ETH_P_IPV6)) {
80		struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;
81		struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst;
82
83		ip6h = data + nh_off;
84		if (ip6h + 1 > data_end)
85			return XDP_DROP;
86
87		if (ip6h->hop_limit <= 1)
88			return XDP_PASS;
89
90		fib_params.family	= AF_INET6;
91		fib_params.flowinfo	= *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;
92		fib_params.l4_protocol	= ip6h->nexthdr;
93		fib_params.sport	= 0;
94		fib_params.dport	= 0;
95		fib_params.tot_len	= ntohs(ip6h->payload_len);
96		*src			= ip6h->saddr;
97		*dst			= ip6h->daddr;
98	} else {
99		return XDP_PASS;
100	}
101
102	fib_params.ifindex = ctx->ingress_ifindex;
103
104	rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
105	/*
106	 * Some rc (return codes) from bpf_fib_lookup() are important,
107	 * to understand how this XDP-prog interacts with network stack.
108	 *
109	 * BPF_FIB_LKUP_RET_NO_NEIGH:
110	 *  Even if route lookup was a success, then the MAC-addresses are also
111	 *  needed.  This is obtained from arp/neighbour table, but if table is
112	 *  (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned.  To avoid
113	 *  doing ARP lookup directly from XDP, then send packet to normal
114	 *  network stack via XDP_PASS and expect it will do ARP resolution.
115	 *
116	 * BPF_FIB_LKUP_RET_FWD_DISABLED:
117	 *  The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding
118	 *  setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not
119	 *  enabled this on ingress device.
120	 */
121	if (rc == BPF_FIB_LKUP_RET_SUCCESS) {
122		/* Verify egress index has been configured as TX-port.
123		 * (Note: User can still have inserted an egress ifindex that
124		 * doesn't support XDP xmit, which will result in packet drops).
125		 *
126		 * Note: lookup in devmap supported since 0cdbb4b09a0.
127		 * If not supported will fail with:
128		 *  cannot pass map_type 14 into func bpf_map_lookup_elem#1:
129		 */
130		if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex))
131			return XDP_PASS;
132
133		if (h_proto == htons(ETH_P_IP))
134			ip_decrease_ttl(iph);
135		else if (h_proto == htons(ETH_P_IPV6))
136			ip6h->hop_limit--;
137
138		memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
139		memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
140		return bpf_redirect_map(&xdp_tx_ports, fib_params.ifindex, 0);
141	}
142
143	return XDP_PASS;
144}
145
146SEC("xdp_fwd")
147int xdp_fwd_prog(struct xdp_md *ctx)
148{
149	return xdp_fwd_flags(ctx, 0);
150}
151
152SEC("xdp_fwd_direct")
153int xdp_fwd_direct_prog(struct xdp_md *ctx)
154{
155	return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);
156}
157
158char _license[] SEC("license") = "GPL";
159