1 // SPDX-License-Identifier: GPL-2.0
2 #include <string.h>
3 #include <netinet/in.h>
4 #include <netinet/tcp.h>
5 #include <linux/bpf.h>
6 #include "bpf_helpers.h"
7
8 char _license[] SEC("license") = "GPL";
9 __u32 _version SEC("version") = 1;
10
11 #define SOL_CUSTOM 0xdeadbeef
12
13 struct sockopt_sk {
14 __u8 val;
15 };
16
17 struct bpf_map_def SEC("maps") socket_storage_map = {
18 .type = BPF_MAP_TYPE_SK_STORAGE,
19 .key_size = sizeof(int),
20 .value_size = sizeof(struct sockopt_sk),
21 .map_flags = BPF_F_NO_PREALLOC,
22 };
23 BPF_ANNOTATE_KV_PAIR(socket_storage_map, int, struct sockopt_sk);
24
25 SEC("cgroup/getsockopt")
_getsockopt(struct bpf_sockopt * ctx)26 int _getsockopt(struct bpf_sockopt *ctx)
27 {
28 __u8 *optval_end = ctx->optval_end;
29 __u8 *optval = ctx->optval;
30 struct sockopt_sk *storage;
31
32 if (ctx->level == SOL_IP && ctx->optname == IP_TOS)
33 /* Not interested in SOL_IP:IP_TOS;
34 * let next BPF program in the cgroup chain or kernel
35 * handle it.
36 */
37 return 1;
38
39 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
40 /* Not interested in SOL_SOCKET:SO_SNDBUF;
41 * let next BPF program in the cgroup chain or kernel
42 * handle it.
43 */
44 return 1;
45 }
46
47 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
48 /* Not interested in SOL_TCP:TCP_CONGESTION;
49 * let next BPF program in the cgroup chain or kernel
50 * handle it.
51 */
52 return 1;
53 }
54
55 if (ctx->level != SOL_CUSTOM)
56 return 0; /* EPERM, deny everything except custom level */
57
58 if (optval + 1 > optval_end)
59 return 0; /* EPERM, bounds check */
60
61 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
62 BPF_SK_STORAGE_GET_F_CREATE);
63 if (!storage)
64 return 0; /* EPERM, couldn't get sk storage */
65
66 if (!ctx->retval)
67 return 0; /* EPERM, kernel should not have handled
68 * SOL_CUSTOM, something is wrong!
69 */
70 ctx->retval = 0; /* Reset system call return value to zero */
71
72 optval[0] = storage->val;
73 ctx->optlen = 1;
74
75 return 1;
76 }
77
78 SEC("cgroup/setsockopt")
_setsockopt(struct bpf_sockopt * ctx)79 int _setsockopt(struct bpf_sockopt *ctx)
80 {
81 __u8 *optval_end = ctx->optval_end;
82 __u8 *optval = ctx->optval;
83 struct sockopt_sk *storage;
84
85 if (ctx->level == SOL_IP && ctx->optname == IP_TOS)
86 /* Not interested in SOL_IP:IP_TOS;
87 * let next BPF program in the cgroup chain or kernel
88 * handle it.
89 */
90 return 1;
91
92 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
93 /* Overwrite SO_SNDBUF value */
94
95 if (optval + sizeof(__u32) > optval_end)
96 return 0; /* EPERM, bounds check */
97
98 *(__u32 *)optval = 0x55AA;
99 ctx->optlen = 4;
100
101 return 1;
102 }
103
104 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
105 /* Always use cubic */
106
107 if (optval + 5 > optval_end)
108 return 0; /* EPERM, bounds check */
109
110 memcpy(optval, "cubic", 5);
111 ctx->optlen = 5;
112
113 return 1;
114 }
115
116 if (ctx->level != SOL_CUSTOM)
117 return 0; /* EPERM, deny everything except custom level */
118
119 if (optval + 1 > optval_end)
120 return 0; /* EPERM, bounds check */
121
122 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
123 BPF_SK_STORAGE_GET_F_CREATE);
124 if (!storage)
125 return 0; /* EPERM, couldn't get sk storage */
126
127 storage->val = optval[0];
128 ctx->optlen = -1; /* BPF has consumed this option, don't call kernel
129 * setsockopt handler.
130 */
131
132 return 1;
133 }
134