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