1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2018 Facebook
3 
4 #include <string.h>
5 
6 #include <linux/stddef.h>
7 #include <linux/bpf.h>
8 #include <linux/in.h>
9 #include <linux/in6.h>
10 #include <sys/socket.h>
11 #include <netinet/tcp.h>
12 
13 #include <bpf/bpf_helpers.h>
14 #include <bpf/bpf_endian.h>
15 
16 #define SRC_REWRITE_IP4		0x7f000004U
17 #define DST_REWRITE_IP4		0x7f000001U
18 #define DST_REWRITE_PORT4	4444
19 
20 #ifndef TCP_CA_NAME_MAX
21 #define TCP_CA_NAME_MAX 16
22 #endif
23 
24 int _version SEC("version") = 1;
25 
26 __attribute__ ((noinline))
27 int do_bind(struct bpf_sock_addr *ctx)
28 {
29 	struct sockaddr_in sa = {};
30 
31 	sa.sin_family = AF_INET;
32 	sa.sin_port = bpf_htons(0);
33 	sa.sin_addr.s_addr = bpf_htonl(SRC_REWRITE_IP4);
34 
35 	if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0)
36 		return 0;
37 
38 	return 1;
39 }
40 
41 static __inline int verify_cc(struct bpf_sock_addr *ctx,
42 			      char expected[TCP_CA_NAME_MAX])
43 {
44 	char buf[TCP_CA_NAME_MAX];
45 	int i;
46 
47 	if (bpf_getsockopt(ctx, SOL_TCP, TCP_CONGESTION, &buf, sizeof(buf)))
48 		return 1;
49 
50 	for (i = 0; i < TCP_CA_NAME_MAX; i++) {
51 		if (buf[i] != expected[i])
52 			return 1;
53 		if (buf[i] == 0)
54 			break;
55 	}
56 
57 	return 0;
58 }
59 
60 static __inline int set_cc(struct bpf_sock_addr *ctx)
61 {
62 	char dctcp[TCP_CA_NAME_MAX] = "dctcp";
63 	char cubic[TCP_CA_NAME_MAX] = "cubic";
64 
65 	if (bpf_setsockopt(ctx, SOL_TCP, TCP_CONGESTION, &dctcp, sizeof(dctcp)))
66 		return 1;
67 	if (verify_cc(ctx, dctcp))
68 		return 1;
69 
70 	if (bpf_setsockopt(ctx, SOL_TCP, TCP_CONGESTION, &cubic, sizeof(cubic)))
71 		return 1;
72 	if (verify_cc(ctx, cubic))
73 		return 1;
74 
75 	return 0;
76 }
77 
78 SEC("cgroup/connect4")
79 int connect_v4_prog(struct bpf_sock_addr *ctx)
80 {
81 	struct bpf_sock_tuple tuple = {};
82 	struct bpf_sock *sk;
83 
84 	/* Verify that new destination is available. */
85 	memset(&tuple.ipv4.saddr, 0, sizeof(tuple.ipv4.saddr));
86 	memset(&tuple.ipv4.sport, 0, sizeof(tuple.ipv4.sport));
87 
88 	tuple.ipv4.daddr = bpf_htonl(DST_REWRITE_IP4);
89 	tuple.ipv4.dport = bpf_htons(DST_REWRITE_PORT4);
90 
91 	if (ctx->type != SOCK_STREAM && ctx->type != SOCK_DGRAM)
92 		return 0;
93 	else if (ctx->type == SOCK_STREAM)
94 		sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof(tuple.ipv4),
95 				       BPF_F_CURRENT_NETNS, 0);
96 	else
97 		sk = bpf_sk_lookup_udp(ctx, &tuple, sizeof(tuple.ipv4),
98 				       BPF_F_CURRENT_NETNS, 0);
99 
100 	if (!sk)
101 		return 0;
102 
103 	if (sk->src_ip4 != tuple.ipv4.daddr ||
104 	    sk->src_port != DST_REWRITE_PORT4) {
105 		bpf_sk_release(sk);
106 		return 0;
107 	}
108 
109 	bpf_sk_release(sk);
110 
111 	/* Rewrite congestion control. */
112 	if (ctx->type == SOCK_STREAM && set_cc(ctx))
113 		return 0;
114 
115 	/* Rewrite destination. */
116 	ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
117 	ctx->user_port = bpf_htons(DST_REWRITE_PORT4);
118 
119 	return do_bind(ctx) ? 1 : 0;
120 }
121 
122 char _license[] SEC("license") = "GPL";
123