1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (c) 2018 Facebook
4  *
5  * BPF program to automatically reflect TOS option from received syn packet
6  *
7  * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
8  */
9 
10 #include <uapi/linux/bpf.h>
11 #include <uapi/linux/tcp.h>
12 #include <uapi/linux/if_ether.h>
13 #include <uapi/linux/if_packet.h>
14 #include <uapi/linux/ip.h>
15 #include <uapi/linux/ipv6.h>
16 #include <uapi/linux/in.h>
17 #include <linux/socket.h>
18 #include "bpf_helpers.h"
19 #include "bpf_endian.h"
20 
21 #define DEBUG 1
22 
23 #define bpf_printk(fmt, ...)					\
24 ({								\
25 	       char ____fmt[] = fmt;				\
26 	       bpf_trace_printk(____fmt, sizeof(____fmt),	\
27 				##__VA_ARGS__);			\
28 })
29 
30 SEC("sockops")
31 int bpf_basertt(struct bpf_sock_ops *skops)
32 {
33 	char header[sizeof(struct ipv6hdr)];
34 	struct ipv6hdr *hdr6;
35 	struct iphdr *hdr;
36 	int hdr_size = 0;
37 	int save_syn = 1;
38 	int tos = 0;
39 	int rv = 0;
40 	int op;
41 
42 	op = (int) skops->op;
43 
44 #ifdef DEBUG
45 	bpf_printk("BPF command: %d\n", op);
46 #endif
47 	switch (op) {
48 	case BPF_SOCK_OPS_TCP_LISTEN_CB:
49 		rv = bpf_setsockopt(skops, SOL_TCP, TCP_SAVE_SYN,
50 				   &save_syn, sizeof(save_syn));
51 		break;
52 	case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
53 		if (skops->family == AF_INET)
54 			hdr_size = sizeof(struct iphdr);
55 		else
56 			hdr_size = sizeof(struct ipv6hdr);
57 		rv = bpf_getsockopt(skops, SOL_TCP, TCP_SAVED_SYN,
58 				    header, hdr_size);
59 		if (!rv) {
60 			if (skops->family == AF_INET) {
61 				hdr = (struct iphdr *) header;
62 				tos = hdr->tos;
63 				if (tos != 0)
64 					bpf_setsockopt(skops, SOL_IP, IP_TOS,
65 						       &tos, sizeof(tos));
66 			} else {
67 				hdr6 = (struct ipv6hdr *) header;
68 				tos = ((hdr6->priority) << 4 |
69 				       (hdr6->flow_lbl[0]) >>  4);
70 				if (tos)
71 					bpf_setsockopt(skops, SOL_IPV6,
72 						       IPV6_TCLASS,
73 						       &tos, sizeof(tos));
74 			}
75 			rv = 0;
76 		}
77 		break;
78 	default:
79 		rv = -1;
80 	}
81 #ifdef DEBUG
82 	bpf_printk("Returning %d\n", rv);
83 #endif
84 	skops->reply = rv;
85 	return 1;
86 }
87 char _license[] SEC("license") = "GPL";
88