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