1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2019 Cloudflare Ltd.
3 // Copyright (c) 2020 Isovalent, Inc.
4 
5 #include <stddef.h>
6 #include <stdbool.h>
7 #include <string.h>
8 #include <linux/bpf.h>
9 #include <linux/if_ether.h>
10 #include <linux/in.h>
11 #include <linux/ip.h>
12 #include <linux/ipv6.h>
13 #include <linux/pkt_cls.h>
14 #include <linux/tcp.h>
15 #include <sys/socket.h>
16 #include <bpf/bpf_helpers.h>
17 #include <bpf/bpf_endian.h>
18 #include "bpf_misc.h"
19 
20 #if defined(IPROUTE2_HAVE_LIBBPF)
21 /* Use a new-style map definition. */
22 struct {
23 	__uint(type, BPF_MAP_TYPE_SOCKMAP);
24 	__type(key, int);
25 	__type(value, __u64);
26 	__uint(pinning, LIBBPF_PIN_BY_NAME);
27 	__uint(max_entries, 1);
28 } server_map SEC(".maps");
29 #else
30 /* Pin map under /sys/fs/bpf/tc/globals/<map name> */
31 #define PIN_GLOBAL_NS 2
32 
33 /* Must match struct bpf_elf_map layout from iproute2 */
34 struct {
35 	__u32 type;
36 	__u32 size_key;
37 	__u32 size_value;
38 	__u32 max_elem;
39 	__u32 flags;
40 	__u32 id;
41 	__u32 pinning;
42 } server_map SEC("maps") = {
43 	.type = BPF_MAP_TYPE_SOCKMAP,
44 	.size_key = sizeof(int),
45 	.size_value  = sizeof(__u64),
46 	.max_elem = 1,
47 	.pinning = PIN_GLOBAL_NS,
48 };
49 #endif
50 
51 char _license[] SEC("license") = "GPL";
52 
53 /* Fill 'tuple' with L3 info, and attempt to find L4. On fail, return NULL. */
54 static inline struct bpf_sock_tuple *
55 get_tuple(struct __sk_buff *skb, bool *ipv4, bool *tcp)
56 {
57 	void *data_end = (void *)(long)skb->data_end;
58 	void *data = (void *)(long)skb->data;
59 	struct bpf_sock_tuple *result;
60 	struct ethhdr *eth;
61 	__u8 proto = 0;
62 	__u64 ihl_len;
63 
64 	eth = (struct ethhdr *)(data);
65 	if (eth + 1 > data_end)
66 		return NULL;
67 
68 	if (eth->h_proto == bpf_htons(ETH_P_IP)) {
69 		struct iphdr *iph = (struct iphdr *)(data + sizeof(*eth));
70 
71 		if (iph + 1 > data_end)
72 			return NULL;
73 		if (iph->ihl != 5)
74 			/* Options are not supported */
75 			return NULL;
76 		ihl_len = iph->ihl * 4;
77 		proto = iph->protocol;
78 		*ipv4 = true;
79 		result = (struct bpf_sock_tuple *)&iph->saddr;
80 	} else if (eth->h_proto == bpf_htons(ETH_P_IPV6)) {
81 		struct ipv6hdr *ip6h = (struct ipv6hdr *)(data + sizeof(*eth));
82 
83 		if (ip6h + 1 > data_end)
84 			return NULL;
85 		ihl_len = sizeof(*ip6h);
86 		proto = ip6h->nexthdr;
87 		*ipv4 = false;
88 		result = (struct bpf_sock_tuple *)&ip6h->saddr;
89 	} else {
90 		return (struct bpf_sock_tuple *)data;
91 	}
92 
93 	if (proto != IPPROTO_TCP && proto != IPPROTO_UDP)
94 		return NULL;
95 
96 	*tcp = (proto == IPPROTO_TCP);
97 	__sink(ihl_len);
98 	return result;
99 }
100 
101 static inline int
102 handle_udp(struct __sk_buff *skb, struct bpf_sock_tuple *tuple, bool ipv4)
103 {
104 	struct bpf_sock *sk;
105 	const int zero = 0;
106 	size_t tuple_len;
107 	__be16 dport;
108 	int ret;
109 
110 	tuple_len = ipv4 ? sizeof(tuple->ipv4) : sizeof(tuple->ipv6);
111 	if ((void *)tuple + tuple_len > (void *)(long)skb->data_end)
112 		return TC_ACT_SHOT;
113 
114 	sk = bpf_sk_lookup_udp(skb, tuple, tuple_len, BPF_F_CURRENT_NETNS, 0);
115 	if (sk)
116 		goto assign;
117 
118 	dport = ipv4 ? tuple->ipv4.dport : tuple->ipv6.dport;
119 	if (dport != bpf_htons(4321))
120 		return TC_ACT_OK;
121 
122 	sk = bpf_map_lookup_elem(&server_map, &zero);
123 	if (!sk)
124 		return TC_ACT_SHOT;
125 
126 assign:
127 	ret = bpf_sk_assign(skb, sk, 0);
128 	bpf_sk_release(sk);
129 	return ret;
130 }
131 
132 static inline int
133 handle_tcp(struct __sk_buff *skb, struct bpf_sock_tuple *tuple, bool ipv4)
134 {
135 	struct bpf_sock *sk;
136 	const int zero = 0;
137 	size_t tuple_len;
138 	__be16 dport;
139 	int ret;
140 
141 	tuple_len = ipv4 ? sizeof(tuple->ipv4) : sizeof(tuple->ipv6);
142 	if ((void *)tuple + tuple_len > (void *)(long)skb->data_end)
143 		return TC_ACT_SHOT;
144 
145 	sk = bpf_skc_lookup_tcp(skb, tuple, tuple_len, BPF_F_CURRENT_NETNS, 0);
146 	if (sk) {
147 		if (sk->state != BPF_TCP_LISTEN)
148 			goto assign;
149 		bpf_sk_release(sk);
150 	}
151 
152 	dport = ipv4 ? tuple->ipv4.dport : tuple->ipv6.dport;
153 	if (dport != bpf_htons(4321))
154 		return TC_ACT_OK;
155 
156 	sk = bpf_map_lookup_elem(&server_map, &zero);
157 	if (!sk)
158 		return TC_ACT_SHOT;
159 
160 	if (sk->state != BPF_TCP_LISTEN) {
161 		bpf_sk_release(sk);
162 		return TC_ACT_SHOT;
163 	}
164 
165 assign:
166 	ret = bpf_sk_assign(skb, sk, 0);
167 	bpf_sk_release(sk);
168 	return ret;
169 }
170 
171 SEC("tc")
172 int bpf_sk_assign_test(struct __sk_buff *skb)
173 {
174 	struct bpf_sock_tuple *tuple;
175 	bool ipv4 = false;
176 	bool tcp = false;
177 	int ret = 0;
178 
179 	tuple = get_tuple(skb, &ipv4, &tcp);
180 	if (!tuple)
181 		return TC_ACT_SHOT;
182 
183 	/* Note that the verifier socket return type for bpf_skc_lookup_tcp()
184 	 * differs from bpf_sk_lookup_udp(), so even though the C-level type is
185 	 * the same here, if we try to share the implementations they will
186 	 * fail to verify because we're crossing pointer types.
187 	 */
188 	if (tcp)
189 		ret = handle_tcp(skb, tuple, ipv4);
190 	else
191 		ret = handle_udp(skb, tuple, ipv4);
192 
193 	return ret == 0 ? TC_ACT_OK : TC_ACT_SHOT;
194 }
195