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") 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") 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