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 __u32 _version SEC("version") = 1;
10
11 #ifndef PAGE_SIZE
12 #define PAGE_SIZE 4096
13 #endif
14
15 #ifndef SOL_TCP
16 #define SOL_TCP IPPROTO_TCP
17 #endif
18
19 #define SOL_CUSTOM 0xdeadbeef
20
21 struct sockopt_sk {
22 __u8 val;
23 };
24
25 struct {
26 __uint(type, BPF_MAP_TYPE_SK_STORAGE);
27 __uint(map_flags, BPF_F_NO_PREALLOC);
28 __type(key, int);
29 __type(value, struct sockopt_sk);
30 } socket_storage_map SEC(".maps");
31
32 SEC("cgroup/getsockopt")
_getsockopt(struct bpf_sockopt *ctx)33 int _getsockopt(struct bpf_sockopt *ctx)
34 {
35 __u8 *optval_end = ctx->optval_end;
36 __u8 *optval = ctx->optval;
37 struct sockopt_sk *storage;
38
39 if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
40 /* Not interested in SOL_IP:IP_TOS;
41 * let next BPF program in the cgroup chain or kernel
42 * handle it.
43 */
44 ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
45 return 1;
46 }
47
48 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
49 /* Not interested in SOL_SOCKET:SO_SNDBUF;
50 * let next BPF program in the cgroup chain or kernel
51 * handle it.
52 */
53 return 1;
54 }
55
56 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
57 /* Not interested in SOL_TCP:TCP_CONGESTION;
58 * let next BPF program in the cgroup chain or kernel
59 * handle it.
60 */
61 return 1;
62 }
63
64 if (ctx->level == SOL_TCP && ctx->optname == TCP_ZEROCOPY_RECEIVE) {
65 /* Verify that TCP_ZEROCOPY_RECEIVE triggers.
66 * It has a custom implementation for performance
67 * reasons.
68 */
69
70 if (optval + sizeof(struct tcp_zerocopy_receive) > optval_end)
71 return 0; /* EPERM, bounds check */
72
73 if (((struct tcp_zerocopy_receive *)optval)->address != 0)
74 return 0; /* EPERM, unexpected data */
75
76 return 1;
77 }
78
79 if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
80 if (optval + 1 > optval_end)
81 return 0; /* EPERM, bounds check */
82
83 ctx->retval = 0; /* Reset system call return value to zero */
84
85 /* Always export 0x55 */
86 optval[0] = 0x55;
87 ctx->optlen = 1;
88
89 /* Userspace buffer is PAGE_SIZE * 2, but BPF
90 * program can only see the first PAGE_SIZE
91 * bytes of data.
92 */
93 if (optval_end - optval != PAGE_SIZE)
94 return 0; /* EPERM, unexpected data size */
95
96 return 1;
97 }
98
99 if (ctx->level != SOL_CUSTOM)
100 return 0; /* EPERM, deny everything except custom level */
101
102 if (optval + 1 > optval_end)
103 return 0; /* EPERM, bounds check */
104
105 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
106 BPF_SK_STORAGE_GET_F_CREATE);
107 if (!storage)
108 return 0; /* EPERM, couldn't get sk storage */
109
110 if (!ctx->retval)
111 return 0; /* EPERM, kernel should not have handled
112 * SOL_CUSTOM, something is wrong!
113 */
114 ctx->retval = 0; /* Reset system call return value to zero */
115
116 optval[0] = storage->val;
117 ctx->optlen = 1;
118
119 return 1;
120 }
121
122 SEC("cgroup/setsockopt")
_setsockopt(struct bpf_sockopt *ctx)123 int _setsockopt(struct bpf_sockopt *ctx)
124 {
125 __u8 *optval_end = ctx->optval_end;
126 __u8 *optval = ctx->optval;
127 struct sockopt_sk *storage;
128
129 if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
130 /* Not interested in SOL_IP:IP_TOS;
131 * let next BPF program in the cgroup chain or kernel
132 * handle it.
133 */
134 ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
135 return 1;
136 }
137
138 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
139 /* Overwrite SO_SNDBUF value */
140
141 if (optval + sizeof(__u32) > optval_end)
142 return 0; /* EPERM, bounds check */
143
144 *(__u32 *)optval = 0x55AA;
145 ctx->optlen = 4;
146
147 return 1;
148 }
149
150 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
151 /* Always use cubic */
152
153 if (optval + 5 > optval_end)
154 return 0; /* EPERM, bounds check */
155
156 memcpy(optval, "cubic", 5);
157 ctx->optlen = 5;
158
159 return 1;
160 }
161
162 if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
163 /* Original optlen is larger than PAGE_SIZE. */
164 if (ctx->optlen != PAGE_SIZE * 2)
165 return 0; /* EPERM, unexpected data size */
166
167 if (optval + 1 > optval_end)
168 return 0; /* EPERM, bounds check */
169
170 /* Make sure we can trim the buffer. */
171 optval[0] = 0;
172 ctx->optlen = 1;
173
174 /* Usepace buffer is PAGE_SIZE * 2, but BPF
175 * program can only see the first PAGE_SIZE
176 * bytes of data.
177 */
178 if (optval_end - optval != PAGE_SIZE)
179 return 0; /* EPERM, unexpected data size */
180
181 return 1;
182 }
183
184 if (ctx->level != SOL_CUSTOM)
185 return 0; /* EPERM, deny everything except custom level */
186
187 if (optval + 1 > optval_end)
188 return 0; /* EPERM, bounds check */
189
190 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
191 BPF_SK_STORAGE_GET_F_CREATE);
192 if (!storage)
193 return 0; /* EPERM, couldn't get sk storage */
194
195 storage->val = optval[0];
196 ctx->optlen = -1; /* BPF has consumed this option, don't call kernel
197 * setsockopt handler.
198 */
199
200 return 1;
201 }
202