1 // SPDX-License-Identifier: GPL-2.0
2 #include <string.h>
3 #include <linux/tcp.h>
4 #include <linux/bpf.h>
5 #include <netinet/in.h>
6 #include <bpf/bpf_helpers.h>
7 
8 char _license[] SEC("license") = "GPL";
9 
10 int page_size = 0; /* userspace should set it */
11 
12 #ifndef SOL_TCP
13 #define SOL_TCP IPPROTO_TCP
14 #endif
15 
16 #define SOL_CUSTOM			0xdeadbeef
17 
18 struct sockopt_sk {
19 	__u8 val;
20 };
21 
22 struct {
23 	__uint(type, BPF_MAP_TYPE_SK_STORAGE);
24 	__uint(map_flags, BPF_F_NO_PREALLOC);
25 	__type(key, int);
26 	__type(value, struct sockopt_sk);
27 } socket_storage_map SEC(".maps");
28 
29 SEC("cgroup/getsockopt")
30 int _getsockopt(struct bpf_sockopt *ctx)
31 {
32 	__u8 *optval_end = ctx->optval_end;
33 	__u8 *optval = ctx->optval;
34 	struct sockopt_sk *storage;
35 	struct bpf_sock *sk;
36 
37 	/* Bypass AF_NETLINK. */
38 	sk = ctx->sk;
39 	if (sk && sk->family == AF_NETLINK)
40 		goto out;
41 
42 	/* Make sure bpf_get_netns_cookie is callable.
43 	 */
44 	if (bpf_get_netns_cookie(NULL) == 0)
45 		return 0;
46 
47 	if (bpf_get_netns_cookie(ctx) == 0)
48 		return 0;
49 
50 	if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
51 		/* Not interested in SOL_IP:IP_TOS;
52 		 * let next BPF program in the cgroup chain or kernel
53 		 * handle it.
54 		 */
55 		goto out;
56 	}
57 
58 	if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
59 		/* Not interested in SOL_SOCKET:SO_SNDBUF;
60 		 * let next BPF program in the cgroup chain or kernel
61 		 * handle it.
62 		 */
63 		goto out;
64 	}
65 
66 	if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
67 		/* Not interested in SOL_TCP:TCP_CONGESTION;
68 		 * let next BPF program in the cgroup chain or kernel
69 		 * handle it.
70 		 */
71 		goto out;
72 	}
73 
74 	if (ctx->level == SOL_TCP && ctx->optname == TCP_ZEROCOPY_RECEIVE) {
75 		/* Verify that TCP_ZEROCOPY_RECEIVE triggers.
76 		 * It has a custom implementation for performance
77 		 * reasons.
78 		 */
79 
80 		/* Check that optval contains address (__u64) */
81 		if (optval + sizeof(__u64) > optval_end)
82 			return 0; /* bounds check */
83 
84 		if (((struct tcp_zerocopy_receive *)optval)->address != 0)
85 			return 0; /* unexpected data */
86 
87 		goto out;
88 	}
89 
90 	if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
91 		if (optval + 1 > optval_end)
92 			return 0; /* bounds check */
93 
94 		ctx->retval = 0; /* Reset system call return value to zero */
95 
96 		/* Always export 0x55 */
97 		optval[0] = 0x55;
98 		ctx->optlen = 1;
99 
100 		/* Userspace buffer is PAGE_SIZE * 2, but BPF
101 		 * program can only see the first PAGE_SIZE
102 		 * bytes of data.
103 		 */
104 		if (optval_end - optval != page_size)
105 			return 0; /* unexpected data size */
106 
107 		return 1;
108 	}
109 
110 	if (ctx->level != SOL_CUSTOM)
111 		return 0; /* deny everything except custom level */
112 
113 	if (optval + 1 > optval_end)
114 		return 0; /* bounds check */
115 
116 	storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
117 				     BPF_SK_STORAGE_GET_F_CREATE);
118 	if (!storage)
119 		return 0; /* couldn't get sk storage */
120 
121 	if (!ctx->retval)
122 		return 0; /* kernel should not have handled
123 			   * SOL_CUSTOM, something is wrong!
124 			   */
125 	ctx->retval = 0; /* Reset system call return value to zero */
126 
127 	optval[0] = storage->val;
128 	ctx->optlen = 1;
129 
130 	return 1;
131 
132 out:
133 	/* optval larger than PAGE_SIZE use kernel's buffer. */
134 	if (ctx->optlen > page_size)
135 		ctx->optlen = 0;
136 	return 1;
137 }
138 
139 SEC("cgroup/setsockopt")
140 int _setsockopt(struct bpf_sockopt *ctx)
141 {
142 	__u8 *optval_end = ctx->optval_end;
143 	__u8 *optval = ctx->optval;
144 	struct sockopt_sk *storage;
145 	struct bpf_sock *sk;
146 
147 	/* Bypass AF_NETLINK. */
148 	sk = ctx->sk;
149 	if (sk && sk->family == AF_NETLINK)
150 		goto out;
151 
152 	/* Make sure bpf_get_netns_cookie is callable.
153 	 */
154 	if (bpf_get_netns_cookie(NULL) == 0)
155 		return 0;
156 
157 	if (bpf_get_netns_cookie(ctx) == 0)
158 		return 0;
159 
160 	if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
161 		/* Not interested in SOL_IP:IP_TOS;
162 		 * let next BPF program in the cgroup chain or kernel
163 		 * handle it.
164 		 */
165 		ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
166 		return 1;
167 	}
168 
169 	if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
170 		/* Overwrite SO_SNDBUF value */
171 
172 		if (optval + sizeof(__u32) > optval_end)
173 			return 0; /* bounds check */
174 
175 		*(__u32 *)optval = 0x55AA;
176 		ctx->optlen = 4;
177 
178 		return 1;
179 	}
180 
181 	if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
182 		/* Always use cubic */
183 
184 		if (optval + 5 > optval_end)
185 			return 0; /* bounds check */
186 
187 		memcpy(optval, "cubic", 5);
188 		ctx->optlen = 5;
189 
190 		return 1;
191 	}
192 
193 	if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
194 		/* Original optlen is larger than PAGE_SIZE. */
195 		if (ctx->optlen != page_size * 2)
196 			return 0; /* unexpected data size */
197 
198 		if (optval + 1 > optval_end)
199 			return 0; /* bounds check */
200 
201 		/* Make sure we can trim the buffer. */
202 		optval[0] = 0;
203 		ctx->optlen = 1;
204 
205 		/* Usepace buffer is PAGE_SIZE * 2, but BPF
206 		 * program can only see the first PAGE_SIZE
207 		 * bytes of data.
208 		 */
209 		if (optval_end - optval != page_size)
210 			return 0; /* unexpected data size */
211 
212 		return 1;
213 	}
214 
215 	if (ctx->level != SOL_CUSTOM)
216 		return 0; /* deny everything except custom level */
217 
218 	if (optval + 1 > optval_end)
219 		return 0; /* bounds check */
220 
221 	storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
222 				     BPF_SK_STORAGE_GET_F_CREATE);
223 	if (!storage)
224 		return 0; /* couldn't get sk storage */
225 
226 	storage->val = optval[0];
227 	ctx->optlen = -1; /* BPF has consumed this option, don't call kernel
228 			   * setsockopt handler.
229 			   */
230 
231 	return 1;
232 
233 out:
234 	/* optval larger than PAGE_SIZE use kernel's buffer. */
235 	if (ctx->optlen > page_size)
236 		ctx->optlen = 0;
237 	return 1;
238 }
239