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")
_getsockopt(struct bpf_sockopt * ctx)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
36 /* Make sure bpf_get_netns_cookie is callable.
37 */
38 if (bpf_get_netns_cookie(NULL) == 0)
39 return 0;
40
41 if (bpf_get_netns_cookie(ctx) == 0)
42 return 0;
43
44 if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
45 /* Not interested in SOL_IP:IP_TOS;
46 * let next BPF program in the cgroup chain or kernel
47 * handle it.
48 */
49 ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
50 return 1;
51 }
52
53 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
54 /* Not interested in SOL_SOCKET:SO_SNDBUF;
55 * let next BPF program in the cgroup chain or kernel
56 * handle it.
57 */
58 return 1;
59 }
60
61 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
62 /* Not interested in SOL_TCP:TCP_CONGESTION;
63 * let next BPF program in the cgroup chain or kernel
64 * handle it.
65 */
66 return 1;
67 }
68
69 if (ctx->level == SOL_TCP && ctx->optname == TCP_ZEROCOPY_RECEIVE) {
70 /* Verify that TCP_ZEROCOPY_RECEIVE triggers.
71 * It has a custom implementation for performance
72 * reasons.
73 */
74
75 /* Check that optval contains address (__u64) */
76 if (optval + sizeof(__u64) > optval_end)
77 return 0; /* bounds check */
78
79 if (((struct tcp_zerocopy_receive *)optval)->address != 0)
80 return 0; /* unexpected data */
81
82 return 1;
83 }
84
85 if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
86 if (optval + 1 > optval_end)
87 return 0; /* bounds check */
88
89 ctx->retval = 0; /* Reset system call return value to zero */
90
91 /* Always export 0x55 */
92 optval[0] = 0x55;
93 ctx->optlen = 1;
94
95 /* Userspace buffer is PAGE_SIZE * 2, but BPF
96 * program can only see the first PAGE_SIZE
97 * bytes of data.
98 */
99 if (optval_end - optval != page_size)
100 return 0; /* unexpected data size */
101
102 return 1;
103 }
104
105 if (ctx->level != SOL_CUSTOM)
106 return 0; /* deny everything except custom level */
107
108 if (optval + 1 > optval_end)
109 return 0; /* bounds check */
110
111 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
112 BPF_SK_STORAGE_GET_F_CREATE);
113 if (!storage)
114 return 0; /* couldn't get sk storage */
115
116 if (!ctx->retval)
117 return 0; /* kernel should not have handled
118 * SOL_CUSTOM, something is wrong!
119 */
120 ctx->retval = 0; /* Reset system call return value to zero */
121
122 optval[0] = storage->val;
123 ctx->optlen = 1;
124
125 return 1;
126 }
127
128 SEC("cgroup/setsockopt")
_setsockopt(struct bpf_sockopt * ctx)129 int _setsockopt(struct bpf_sockopt *ctx)
130 {
131 __u8 *optval_end = ctx->optval_end;
132 __u8 *optval = ctx->optval;
133 struct sockopt_sk *storage;
134
135 /* Make sure bpf_get_netns_cookie is callable.
136 */
137 if (bpf_get_netns_cookie(NULL) == 0)
138 return 0;
139
140 if (bpf_get_netns_cookie(ctx) == 0)
141 return 0;
142
143 if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
144 /* Not interested in SOL_IP:IP_TOS;
145 * let next BPF program in the cgroup chain or kernel
146 * handle it.
147 */
148 ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
149 return 1;
150 }
151
152 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
153 /* Overwrite SO_SNDBUF value */
154
155 if (optval + sizeof(__u32) > optval_end)
156 return 0; /* bounds check */
157
158 *(__u32 *)optval = 0x55AA;
159 ctx->optlen = 4;
160
161 return 1;
162 }
163
164 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
165 /* Always use cubic */
166
167 if (optval + 5 > optval_end)
168 return 0; /* bounds check */
169
170 memcpy(optval, "cubic", 5);
171 ctx->optlen = 5;
172
173 return 1;
174 }
175
176 if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
177 /* Original optlen is larger than PAGE_SIZE. */
178 if (ctx->optlen != page_size * 2)
179 return 0; /* unexpected data size */
180
181 if (optval + 1 > optval_end)
182 return 0; /* bounds check */
183
184 /* Make sure we can trim the buffer. */
185 optval[0] = 0;
186 ctx->optlen = 1;
187
188 /* Usepace buffer is PAGE_SIZE * 2, but BPF
189 * program can only see the first PAGE_SIZE
190 * bytes of data.
191 */
192 if (optval_end - optval != page_size)
193 return 0; /* unexpected data size */
194
195 return 1;
196 }
197
198 if (ctx->level != SOL_CUSTOM)
199 return 0; /* deny everything except custom level */
200
201 if (optval + 1 > optval_end)
202 return 0; /* bounds check */
203
204 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
205 BPF_SK_STORAGE_GET_F_CREATE);
206 if (!storage)
207 return 0; /* couldn't get sk storage */
208
209 storage->val = optval[0];
210 ctx->optlen = -1; /* BPF has consumed this option, don't call kernel
211 * setsockopt handler.
212 */
213
214 return 1;
215 }
216