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
26 struct {
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 */
34 static __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
43 static __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
146 SEC("xdp_fwd")
147 int xdp_fwd_prog(struct xdp_md *ctx)
148 {
149 return xdp_fwd_flags(ctx, 0);
150 }
151
152 SEC("xdp_fwd_direct")
153 int xdp_fwd_direct_prog(struct xdp_md *ctx)
154 {
155 return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);
156 }
157
158 char _license[] SEC("license") = "GPL";
159
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