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/bpf_helpers.h>
7 
8 char _license[] SEC("license") = "GPL";
9 __u32 _version SEC("version") = 1;
10 
11 #ifndef PAGE_SIZE
12 #define PAGE_SIZE 4096
13 #endif
14 
15 #define SOL_CUSTOM			0xdeadbeef
16 
17 struct sockopt_sk {
18 	__u8 val;
19 };
20 
21 struct {
22 	__uint(type, BPF_MAP_TYPE_SK_STORAGE);
23 	__uint(map_flags, BPF_F_NO_PREALLOC);
24 	__type(key, int);
25 	__type(value, struct sockopt_sk);
26 } socket_storage_map SEC(".maps");
27 
28 SEC("cgroup/getsockopt")
29 int _getsockopt(struct bpf_sockopt *ctx)
30 {
31 	__u8 *optval_end = ctx->optval_end;
32 	__u8 *optval = ctx->optval;
33 	struct sockopt_sk *storage;
34 
35 	if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
36 		/* Not interested in SOL_IP:IP_TOS;
37 		 * let next BPF program in the cgroup chain or kernel
38 		 * handle it.
39 		 */
40 		ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
41 		return 1;
42 	}
43 
44 	if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
45 		/* Not interested in SOL_SOCKET:SO_SNDBUF;
46 		 * let next BPF program in the cgroup chain or kernel
47 		 * handle it.
48 		 */
49 		return 1;
50 	}
51 
52 	if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
53 		/* Not interested in SOL_TCP:TCP_CONGESTION;
54 		 * let next BPF program in the cgroup chain or kernel
55 		 * handle it.
56 		 */
57 		return 1;
58 	}
59 
60 	if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
61 		if (optval + 1 > optval_end)
62 			return 0; /* EPERM, bounds check */
63 
64 		ctx->retval = 0; /* Reset system call return value to zero */
65 
66 		/* Always export 0x55 */
67 		optval[0] = 0x55;
68 		ctx->optlen = 1;
69 
70 		/* Userspace buffer is PAGE_SIZE * 2, but BPF
71 		 * program can only see the first PAGE_SIZE
72 		 * bytes of data.
73 		 */
74 		if (optval_end - optval != PAGE_SIZE)
75 			return 0; /* EPERM, unexpected data size */
76 
77 		return 1;
78 	}
79 
80 	if (ctx->level != SOL_CUSTOM)
81 		return 0; /* EPERM, deny everything except custom level */
82 
83 	if (optval + 1 > optval_end)
84 		return 0; /* EPERM, bounds check */
85 
86 	storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
87 				     BPF_SK_STORAGE_GET_F_CREATE);
88 	if (!storage)
89 		return 0; /* EPERM, couldn't get sk storage */
90 
91 	if (!ctx->retval)
92 		return 0; /* EPERM, kernel should not have handled
93 			   * SOL_CUSTOM, something is wrong!
94 			   */
95 	ctx->retval = 0; /* Reset system call return value to zero */
96 
97 	optval[0] = storage->val;
98 	ctx->optlen = 1;
99 
100 	return 1;
101 }
102 
103 SEC("cgroup/setsockopt")
104 int _setsockopt(struct bpf_sockopt *ctx)
105 {
106 	__u8 *optval_end = ctx->optval_end;
107 	__u8 *optval = ctx->optval;
108 	struct sockopt_sk *storage;
109 
110 	if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
111 		/* Not interested in SOL_IP:IP_TOS;
112 		 * let next BPF program in the cgroup chain or kernel
113 		 * handle it.
114 		 */
115 		ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
116 		return 1;
117 	}
118 
119 	if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
120 		/* Overwrite SO_SNDBUF value */
121 
122 		if (optval + sizeof(__u32) > optval_end)
123 			return 0; /* EPERM, bounds check */
124 
125 		*(__u32 *)optval = 0x55AA;
126 		ctx->optlen = 4;
127 
128 		return 1;
129 	}
130 
131 	if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
132 		/* Always use cubic */
133 
134 		if (optval + 5 > optval_end)
135 			return 0; /* EPERM, bounds check */
136 
137 		memcpy(optval, "cubic", 5);
138 		ctx->optlen = 5;
139 
140 		return 1;
141 	}
142 
143 	if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
144 		/* Original optlen is larger than PAGE_SIZE. */
145 		if (ctx->optlen != PAGE_SIZE * 2)
146 			return 0; /* EPERM, unexpected data size */
147 
148 		if (optval + 1 > optval_end)
149 			return 0; /* EPERM, bounds check */
150 
151 		/* Make sure we can trim the buffer. */
152 		optval[0] = 0;
153 		ctx->optlen = 1;
154 
155 		/* Usepace buffer is PAGE_SIZE * 2, but BPF
156 		 * program can only see the first PAGE_SIZE
157 		 * bytes of data.
158 		 */
159 		if (optval_end - optval != PAGE_SIZE)
160 			return 0; /* EPERM, unexpected data size */
161 
162 		return 1;
163 	}
164 
165 	if (ctx->level != SOL_CUSTOM)
166 		return 0; /* EPERM, deny everything except custom level */
167 
168 	if (optval + 1 > optval_end)
169 		return 0; /* EPERM, bounds check */
170 
171 	storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
172 				     BPF_SK_STORAGE_GET_F_CREATE);
173 	if (!storage)
174 		return 0; /* EPERM, couldn't get sk storage */
175 
176 	storage->val = optval[0];
177 	ctx->optlen = -1; /* BPF has consumed this option, don't call kernel
178 			   * setsockopt handler.
179 			   */
180 
181 	return 1;
182 }
183