1 // SPDX-License-Identifier: GPL-2.0 2 #include <string.h> 3 #include <netinet/in.h> 4 #include <netinet/tcp.h> 5 #include <linux/bpf.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 #define SOL_CUSTOM 0xdeadbeef 16 17 struct sockopt_sk { 18 __u8 val; 19 }; 20 21 struct { 22 __uint(type, BPF_MAP_TYPE_SK_STORAGE); 23 __uint(map_flags, BPF_F_NO_PREALLOC); 24 __type(key, int); 25 __type(value, struct sockopt_sk); 26 } socket_storage_map SEC(".maps"); 27 28 SEC("cgroup/getsockopt") 29 int _getsockopt(struct bpf_sockopt *ctx) 30 { 31 __u8 *optval_end = ctx->optval_end; 32 __u8 *optval = ctx->optval; 33 struct sockopt_sk *storage; 34 35 if (ctx->level == SOL_IP && ctx->optname == IP_TOS) { 36 /* Not interested in SOL_IP:IP_TOS; 37 * let next BPF program in the cgroup chain or kernel 38 * handle it. 39 */ 40 ctx->optlen = 0; /* bypass optval>PAGE_SIZE */ 41 return 1; 42 } 43 44 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) { 45 /* Not interested in SOL_SOCKET:SO_SNDBUF; 46 * let next BPF program in the cgroup chain or kernel 47 * handle it. 48 */ 49 return 1; 50 } 51 52 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) { 53 /* Not interested in SOL_TCP:TCP_CONGESTION; 54 * let next BPF program in the cgroup chain or kernel 55 * handle it. 56 */ 57 return 1; 58 } 59 60 if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) { 61 if (optval + 1 > optval_end) 62 return 0; /* EPERM, bounds check */ 63 64 ctx->retval = 0; /* Reset system call return value to zero */ 65 66 /* Always export 0x55 */ 67 optval[0] = 0x55; 68 ctx->optlen = 1; 69 70 /* Userspace buffer is PAGE_SIZE * 2, but BPF 71 * program can only see the first PAGE_SIZE 72 * bytes of data. 73 */ 74 if (optval_end - optval != PAGE_SIZE) 75 return 0; /* EPERM, unexpected data size */ 76 77 return 1; 78 } 79 80 if (ctx->level != SOL_CUSTOM) 81 return 0; /* EPERM, deny everything except custom level */ 82 83 if (optval + 1 > optval_end) 84 return 0; /* EPERM, bounds check */ 85 86 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0, 87 BPF_SK_STORAGE_GET_F_CREATE); 88 if (!storage) 89 return 0; /* EPERM, couldn't get sk storage */ 90 91 if (!ctx->retval) 92 return 0; /* EPERM, kernel should not have handled 93 * SOL_CUSTOM, something is wrong! 94 */ 95 ctx->retval = 0; /* Reset system call return value to zero */ 96 97 optval[0] = storage->val; 98 ctx->optlen = 1; 99 100 return 1; 101 } 102 103 SEC("cgroup/setsockopt") 104 int _setsockopt(struct bpf_sockopt *ctx) 105 { 106 __u8 *optval_end = ctx->optval_end; 107 __u8 *optval = ctx->optval; 108 struct sockopt_sk *storage; 109 110 if (ctx->level == SOL_IP && ctx->optname == IP_TOS) { 111 /* Not interested in SOL_IP:IP_TOS; 112 * let next BPF program in the cgroup chain or kernel 113 * handle it. 114 */ 115 ctx->optlen = 0; /* bypass optval>PAGE_SIZE */ 116 return 1; 117 } 118 119 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) { 120 /* Overwrite SO_SNDBUF value */ 121 122 if (optval + sizeof(__u32) > optval_end) 123 return 0; /* EPERM, bounds check */ 124 125 *(__u32 *)optval = 0x55AA; 126 ctx->optlen = 4; 127 128 return 1; 129 } 130 131 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) { 132 /* Always use cubic */ 133 134 if (optval + 5 > optval_end) 135 return 0; /* EPERM, bounds check */ 136 137 memcpy(optval, "cubic", 5); 138 ctx->optlen = 5; 139 140 return 1; 141 } 142 143 if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) { 144 /* Original optlen is larger than PAGE_SIZE. */ 145 if (ctx->optlen != PAGE_SIZE * 2) 146 return 0; /* EPERM, unexpected data size */ 147 148 if (optval + 1 > optval_end) 149 return 0; /* EPERM, bounds check */ 150 151 /* Make sure we can trim the buffer. */ 152 optval[0] = 0; 153 ctx->optlen = 1; 154 155 /* Usepace buffer is PAGE_SIZE * 2, but BPF 156 * program can only see the first PAGE_SIZE 157 * bytes of data. 158 */ 159 if (optval_end - optval != PAGE_SIZE) 160 return 0; /* EPERM, unexpected data size */ 161 162 return 1; 163 } 164 165 if (ctx->level != SOL_CUSTOM) 166 return 0; /* EPERM, deny everything except custom level */ 167 168 if (optval + 1 > optval_end) 169 return 0; /* EPERM, bounds check */ 170 171 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0, 172 BPF_SK_STORAGE_GET_F_CREATE); 173 if (!storage) 174 return 0; /* EPERM, couldn't get sk storage */ 175 176 storage->val = optval[0]; 177 ctx->optlen = -1; /* BPF has consumed this option, don't call kernel 178 * setsockopt handler. 179 */ 180 181 return 1; 182 } 183