tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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 */
23struct {
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
39char _license[] SEC("license") = "GPL";
40
41/* Fill 'tuple' with L3 info, and attempt to find L4. On fail, return NULL. */
42static inline struct bpf_sock_tuple *
43get_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
89static inline int
90handle_udp(struct __sk_buff *skb, struct bpf_sock_tuple *tuple, bool ipv4)
91{
92 struct bpf_sock_tuple ln = {0};
93 struct bpf_sock *sk;
94 const int zero = 0;
95 size_t tuple_len;
96 __be16 dport;
97 int ret;
98
99 tuple_len = ipv4 ? sizeof(tuple->ipv4) : sizeof(tuple->ipv6);
100 if ((void *)tuple + tuple_len > (void *)(long)skb->data_end)
101 return TC_ACT_SHOT;
102
103 sk = bpf_sk_lookup_udp(skb, tuple, tuple_len, BPF_F_CURRENT_NETNS, 0);
104 if (sk)
105 goto assign;
106
107 dport = ipv4 ? tuple->ipv4.dport : tuple->ipv6.dport;
108 if (dport != bpf_htons(4321))
109 return TC_ACT_OK;
110
111 sk = bpf_map_lookup_elem(&server_map, &zero);
112 if (!sk)
113 return TC_ACT_SHOT;
114
115assign:
116 ret = bpf_sk_assign(skb, sk, 0);
117 bpf_sk_release(sk);
118 return ret;
119}
120
121static inline int
122handle_tcp(struct __sk_buff *skb, struct bpf_sock_tuple *tuple, bool ipv4)
123{
124 struct bpf_sock_tuple ln = {0};
125 struct bpf_sock *sk;
126 const int zero = 0;
127 size_t tuple_len;
128 __be16 dport;
129 int ret;
130
131 tuple_len = ipv4 ? sizeof(tuple->ipv4) : sizeof(tuple->ipv6);
132 if ((void *)tuple + tuple_len > (void *)(long)skb->data_end)
133 return TC_ACT_SHOT;
134
135 sk = bpf_skc_lookup_tcp(skb, tuple, tuple_len, BPF_F_CURRENT_NETNS, 0);
136 if (sk) {
137 if (sk->state != BPF_TCP_LISTEN)
138 goto assign;
139 bpf_sk_release(sk);
140 }
141
142 dport = ipv4 ? tuple->ipv4.dport : tuple->ipv6.dport;
143 if (dport != bpf_htons(4321))
144 return TC_ACT_OK;
145
146 sk = bpf_map_lookup_elem(&server_map, &zero);
147 if (!sk)
148 return TC_ACT_SHOT;
149
150 if (sk->state != BPF_TCP_LISTEN) {
151 bpf_sk_release(sk);
152 return TC_ACT_SHOT;
153 }
154
155assign:
156 ret = bpf_sk_assign(skb, sk, 0);
157 bpf_sk_release(sk);
158 return ret;
159}
160
161SEC("tc")
162int bpf_sk_assign_test(struct __sk_buff *skb)
163{
164 struct bpf_sock_tuple *tuple, ln = {0};
165 bool ipv4 = false;
166 bool tcp = false;
167 int tuple_len;
168 int ret = 0;
169
170 tuple = get_tuple(skb, &ipv4, &tcp);
171 if (!tuple)
172 return TC_ACT_SHOT;
173
174 /* Note that the verifier socket return type for bpf_skc_lookup_tcp()
175 * differs from bpf_sk_lookup_udp(), so even though the C-level type is
176 * the same here, if we try to share the implementations they will
177 * fail to verify because we're crossing pointer types.
178 */
179 if (tcp)
180 ret = handle_tcp(skb, tuple, ipv4);
181 else
182 ret = handle_udp(skb, tuple, ipv4);
183
184 return ret == 0 ? TC_ACT_OK : TC_ACT_SHOT;
185}