1// SPDX-License-Identifier: GPL-2.0
2
3/* This logic is lifted from a real-world use case of packet parsing, used in
4 * the open source library katran, a layer 4 load balancer.
5 *
6 * This test demonstrates how to parse packet contents using dynptrs. The
7 * original code (parsing without dynptrs) can be found in test_parse_tcp_hdr_opt.c
8 */
9
10#include <linux/bpf.h>
11#include <bpf/bpf_helpers.h>
12#include <linux/tcp.h>
13#include <stdbool.h>
14#include <linux/ipv6.h>
15#include <linux/if_ether.h>
16#include "test_tcp_hdr_options.h"
17#include "bpf_kfuncs.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
30static int parse_hdr_opt(struct bpf_dynptr *ptr, __u32 *off, __u8 *hdr_bytes_remaining,
31			 __u32 *server_id)
32{
33	__u8 kind, hdr_len;
34	__u8 buffer[sizeof(kind) + sizeof(hdr_len) + sizeof(*server_id)];
35	__u8 *data;
36
37	__builtin_memset(buffer, 0, sizeof(buffer));
38
39	data = bpf_dynptr_slice(ptr, *off, buffer, sizeof(buffer));
40	if (!data)
41		return -1;
42
43	kind = data[0];
44
45	if (kind == TCPOPT_EOL)
46		return -1;
47
48	if (kind == TCPOPT_NOP) {
49		*off += 1;
50		*hdr_bytes_remaining -= 1;
51		return 0;
52	}
53
54	if (*hdr_bytes_remaining < 2)
55		return -1;
56
57	hdr_len = data[1];
58	if (hdr_len > *hdr_bytes_remaining)
59		return -1;
60
61	if (kind == tcp_hdr_opt_kind_tpr) {
62		if (hdr_len != tcp_hdr_opt_len_tpr)
63			return -1;
64
65		__builtin_memcpy(server_id, (__u32 *)(data + 2), sizeof(*server_id));
66		return 1;
67	}
68
69	*off += hdr_len;
70	*hdr_bytes_remaining -= hdr_len;
71	return 0;
72}
73
74SEC("xdp")
75int xdp_ingress_v6(struct xdp_md *xdp)
76{
77	__u8 buffer[sizeof(struct tcphdr)] = {};
78	__u8 hdr_bytes_remaining;
79	struct tcphdr *tcp_hdr;
80	__u8 tcp_hdr_opt_len;
81	int err = 0;
82	__u32 off;
83
84	struct bpf_dynptr ptr;
85
86	bpf_dynptr_from_xdp(xdp, 0, &ptr);
87
88	off = sizeof(struct ethhdr) + sizeof(struct ipv6hdr);
89
90	tcp_hdr = bpf_dynptr_slice(&ptr, off, buffer, sizeof(buffer));
91	if (!tcp_hdr)
92		return XDP_DROP;
93
94	tcp_hdr_opt_len = (tcp_hdr->doff * 4) - sizeof(struct tcphdr);
95	if (tcp_hdr_opt_len < tcp_hdr_opt_len_tpr)
96		return XDP_DROP;
97
98	hdr_bytes_remaining = tcp_hdr_opt_len;
99
100	off += sizeof(struct tcphdr);
101
102	/* max number of bytes of options in tcp header is 40 bytes */
103	for (int i = 0; i < tcp_hdr_opt_max_opt_checks; i++) {
104		err = parse_hdr_opt(&ptr, &off, &hdr_bytes_remaining, &server_id);
105
106		if (err || !hdr_bytes_remaining)
107			break;
108	}
109
110	if (!server_id)
111		return XDP_DROP;
112
113	return XDP_PASS;
114}
115