1// SPDX-License-Identifier: GPL-2.0
2
3/* This parsing logic is taken from the open source library katran, a layer 4
4 * load balancer.
5 *
6 * This code logic using dynptrs can be found in test_parse_tcp_hdr_opt_dynptr.c
7 *
8 * https://github.com/facebookincubator/katran/blob/main/katran/lib/bpf/pckt_parsing.h
9 */
10
11#include <linux/bpf.h>
12#include <bpf/bpf_helpers.h>
13#include <linux/tcp.h>
14#include <stdbool.h>
15#include <linux/ipv6.h>
16#include <linux/if_ether.h>
17#include "test_tcp_hdr_options.h"
18
19char _license[] SEC("license") = "GPL";
20
21/* Kind number used for experiments */
22const __u32 tcp_hdr_opt_kind_tpr = 0xFD;
23/* Length of the tcp header option */
24const __u32 tcp_hdr_opt_len_tpr = 6;
25/* maximum number of header options to check to lookup server_id */
26const __u32 tcp_hdr_opt_max_opt_checks = 15;
27
28__u32 server_id;
29
30struct hdr_opt_state {
31	__u32 server_id;
32	__u8 byte_offset;
33	__u8 hdr_bytes_remaining;
34};
35
36static int parse_hdr_opt(const struct xdp_md *xdp, struct hdr_opt_state *state)
37{
38	const void *data = (void *)(long)xdp->data;
39	const void *data_end = (void *)(long)xdp->data_end;
40	__u8 *tcp_opt, kind, hdr_len;
41
42	tcp_opt = (__u8 *)(data + state->byte_offset);
43	if (tcp_opt + 1 > data_end)
44		return -1;
45
46	kind = tcp_opt[0];
47
48	if (kind == TCPOPT_EOL)
49		return -1;
50
51	if (kind == TCPOPT_NOP) {
52		state->hdr_bytes_remaining--;
53		state->byte_offset++;
54		return 0;
55	}
56
57	if (state->hdr_bytes_remaining < 2 ||
58	    tcp_opt + sizeof(__u8) + sizeof(__u8) > data_end)
59		return -1;
60
61	hdr_len = tcp_opt[1];
62	if (hdr_len > state->hdr_bytes_remaining)
63		return -1;
64
65	if (kind == tcp_hdr_opt_kind_tpr) {
66		if (hdr_len != tcp_hdr_opt_len_tpr)
67			return -1;
68
69		if (tcp_opt + tcp_hdr_opt_len_tpr > data_end)
70			return -1;
71
72		state->server_id = *(__u32 *)&tcp_opt[2];
73		return 1;
74	}
75
76	state->hdr_bytes_remaining -= hdr_len;
77	state->byte_offset += hdr_len;
78	return 0;
79}
80
81SEC("xdp")
82int xdp_ingress_v6(struct xdp_md *xdp)
83{
84	const void *data = (void *)(long)xdp->data;
85	const void *data_end = (void *)(long)xdp->data_end;
86	struct hdr_opt_state opt_state = {};
87	__u8 tcp_hdr_opt_len = 0;
88	struct tcphdr *tcp_hdr;
89	__u64 tcp_offset = 0;
90	int err;
91
92	tcp_offset = sizeof(struct ethhdr) + sizeof(struct ipv6hdr);
93	tcp_hdr = (struct tcphdr *)(data + tcp_offset);
94	if (tcp_hdr + 1 > data_end)
95		return XDP_DROP;
96
97	tcp_hdr_opt_len = (tcp_hdr->doff * 4) - sizeof(struct tcphdr);
98	if (tcp_hdr_opt_len < tcp_hdr_opt_len_tpr)
99		return XDP_DROP;
100
101	opt_state.hdr_bytes_remaining = tcp_hdr_opt_len;
102	opt_state.byte_offset = sizeof(struct tcphdr) + tcp_offset;
103
104	/* max number of bytes of options in tcp header is 40 bytes */
105	for (int i = 0; i < tcp_hdr_opt_max_opt_checks; i++) {
106		err = parse_hdr_opt(xdp, &opt_state);
107
108		if (err || !opt_state.hdr_bytes_remaining)
109			break;
110	}
111
112	if (!opt_state.server_id)
113		return XDP_DROP;
114
115	server_id = opt_state.server_id;
116
117	return XDP_PASS;
118}
119