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