1 // SPDX-License-Identifier: GPL-2.0
2 /* Copyright (c) 2021 Facebook */
3 #include "bpf_iter.h"
4 #include "bpf_tracing_net.h"
5 #include <bpf/bpf_helpers.h>
6 #include <bpf/bpf_endian.h>
7 
8 #define bpf_tcp_sk(skc)	({				\
9 	struct sock_common *_skc = skc;			\
10 	sk = NULL;					\
11 	tp = NULL;					\
12 	if (_skc) {					\
13 		tp = bpf_skc_to_tcp_sock(_skc);		\
14 		sk = (struct sock *)tp;			\
15 	}						\
16 	tp;						\
17 })
18 
19 unsigned short reuse_listen_hport = 0;
20 unsigned short listen_hport = 0;
21 char cubic_cc[TCP_CA_NAME_MAX] = "bpf_cubic";
22 char dctcp_cc[TCP_CA_NAME_MAX] = "bpf_dctcp";
23 bool random_retry = false;
24 
25 static bool tcp_cc_eq(const char *a, const char *b)
26 {
27 	int i;
28 
29 	for (i = 0; i < TCP_CA_NAME_MAX; i++) {
30 		if (a[i] != b[i])
31 			return false;
32 		if (!a[i])
33 			break;
34 	}
35 
36 	return true;
37 }
38 
39 SEC("iter/tcp")
40 int change_tcp_cc(struct bpf_iter__tcp *ctx)
41 {
42 	char cur_cc[TCP_CA_NAME_MAX];
43 	struct tcp_sock *tp;
44 	struct sock *sk;
45 	int ret;
46 
47 	if (!bpf_tcp_sk(ctx->sk_common))
48 		return 0;
49 
50 	if (sk->sk_family != AF_INET6 ||
51 	    (sk->sk_state != TCP_LISTEN &&
52 	     sk->sk_state != TCP_ESTABLISHED) ||
53 	    (sk->sk_num != reuse_listen_hport &&
54 	     sk->sk_num != listen_hport &&
55 	     bpf_ntohs(sk->sk_dport) != listen_hport))
56 		return 0;
57 
58 	if (bpf_getsockopt(tp, SOL_TCP, TCP_CONGESTION,
59 			   cur_cc, sizeof(cur_cc)))
60 		return 0;
61 
62 	if (!tcp_cc_eq(cur_cc, cubic_cc))
63 		return 0;
64 
65 	if (random_retry && bpf_get_prandom_u32() % 4 == 1)
66 		return 1;
67 
68 	bpf_setsockopt(tp, SOL_TCP, TCP_CONGESTION, dctcp_cc, sizeof(dctcp_cc));
69 	return 0;
70 }
71 
72 char _license[] SEC("license") = "GPL";
73