1// SPDX-License-Identifier: GPL-2.0
2#include <stdint.h>
3#include <linux/bpf.h>
4#include <linux/if_ether.h>
5#include <linux/stddef.h>
6#include <linux/in.h>
7#include <linux/ip.h>
8#include <linux/pkt_cls.h>
9#include <linux/tcp.h>
10#include <bpf/bpf_helpers.h>
11#include <bpf/bpf_endian.h>
12
13/* the maximum delay we are willing to add (drop packets beyond that) */
14#define TIME_HORIZON_NS (2000 * 1000 * 1000)
15#define NS_PER_SEC 1000000000
16#define ECN_HORIZON_NS 5000000
17#define THROTTLE_RATE_BPS (5 * 1000 * 1000)
18
19/* flow_key => last_tstamp timestamp used */
20struct {
21	__uint(type, BPF_MAP_TYPE_HASH);
22	__type(key, uint32_t);
23	__type(value, uint64_t);
24	__uint(max_entries, 1);
25} flow_map SEC(".maps");
26
27static inline int throttle_flow(struct __sk_buff *skb)
28{
29	int key = 0;
30	uint64_t *last_tstamp = bpf_map_lookup_elem(&flow_map, &key);
31	uint64_t delay_ns = ((uint64_t)skb->len) * NS_PER_SEC /
32			THROTTLE_RATE_BPS;
33	uint64_t now = bpf_ktime_get_ns();
34	uint64_t tstamp, next_tstamp = 0;
35
36	if (last_tstamp)
37		next_tstamp = *last_tstamp + delay_ns;
38
39	tstamp = skb->tstamp;
40	if (tstamp < now)
41		tstamp = now;
42
43	/* should we throttle? */
44	if (next_tstamp <= tstamp) {
45		if (bpf_map_update_elem(&flow_map, &key, &tstamp, BPF_ANY))
46			return TC_ACT_SHOT;
47		return TC_ACT_OK;
48	}
49
50	/* do not queue past the time horizon */
51	if (next_tstamp - now >= TIME_HORIZON_NS)
52		return TC_ACT_SHOT;
53
54	/* set ecn bit, if needed */
55	if (next_tstamp - now >= ECN_HORIZON_NS)
56		bpf_skb_ecn_set_ce(skb);
57
58	if (bpf_map_update_elem(&flow_map, &key, &next_tstamp, BPF_EXIST))
59		return TC_ACT_SHOT;
60	skb->tstamp = next_tstamp;
61
62	return TC_ACT_OK;
63}
64
65static inline int handle_tcp(struct __sk_buff *skb, struct tcphdr *tcp)
66{
67	void *data_end = (void *)(long)skb->data_end;
68
69	/* drop malformed packets */
70	if ((void *)(tcp + 1) > data_end)
71		return TC_ACT_SHOT;
72
73	if (tcp->dest == bpf_htons(9000))
74		return throttle_flow(skb);
75
76	return TC_ACT_OK;
77}
78
79static inline int handle_ipv4(struct __sk_buff *skb)
80{
81	void *data_end = (void *)(long)skb->data_end;
82	void *data = (void *)(long)skb->data;
83	struct iphdr *iph;
84	uint32_t ihl;
85
86	/* drop malformed packets */
87	if (data + sizeof(struct ethhdr) > data_end)
88		return TC_ACT_SHOT;
89	iph = (struct iphdr *)(data + sizeof(struct ethhdr));
90	if ((void *)(iph + 1) > data_end)
91		return TC_ACT_SHOT;
92	ihl = iph->ihl * 4;
93	if (((void *)iph) + ihl > data_end)
94		return TC_ACT_SHOT;
95
96	if (iph->protocol == IPPROTO_TCP)
97		return handle_tcp(skb, (struct tcphdr *)(((void *)iph) + ihl));
98
99	return TC_ACT_OK;
100}
101
102SEC("cls_test") int tc_prog(struct __sk_buff *skb)
103{
104	if (skb->protocol == bpf_htons(ETH_P_IP))
105		return handle_ipv4(skb);
106
107	return TC_ACT_OK;
108}
109
110char __license[] SEC("license") = "GPL";
111