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 */
20 struct {
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
27 static 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
65 static 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
79 static 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
102 SEC("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
110 char __license[] SEC("license") = "GPL";
111
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