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
19 char _license[] SEC("license") = "GPL";
20
21 /* Kind number used for experiments */
22 const __u32 tcp_hdr_opt_kind_tpr = 0xFD;
23 /* Length of the tcp header option */
24 const __u32 tcp_hdr_opt_len_tpr = 6;
25 /* maximum number of header options to check to lookup server_id */
26 const __u32 tcp_hdr_opt_max_opt_checks = 15;
27
28 __u32 server_id;
29
parse_hdr_opt(struct bpf_dynptr * ptr,__u32 * off,__u8 * hdr_bytes_remaining,__u32 * server_id)30 static 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
74 SEC("xdp")
xdp_ingress_v6(struct xdp_md * xdp)75 int 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
