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_helpers.h" 7 8 char _license[] SEC("license") = "GPL"; 9 __u32 _version SEC("version") = 1; 10 11 #define SOL_CUSTOM 0xdeadbeef 12 13 struct sockopt_sk { 14 __u8 val; 15 }; 16 17 struct bpf_map_def SEC("maps") socket_storage_map = { 18 .type = BPF_MAP_TYPE_SK_STORAGE, 19 .key_size = sizeof(int), 20 .value_size = sizeof(struct sockopt_sk), 21 .map_flags = BPF_F_NO_PREALLOC, 22 }; 23 BPF_ANNOTATE_KV_PAIR(socket_storage_map, int, struct sockopt_sk); 24 25 SEC("cgroup/getsockopt") 26 int _getsockopt(struct bpf_sockopt *ctx) 27 { 28 __u8 *optval_end = ctx->optval_end; 29 __u8 *optval = ctx->optval; 30 struct sockopt_sk *storage; 31 32 if (ctx->level == SOL_IP && ctx->optname == IP_TOS) 33 /* Not interested in SOL_IP:IP_TOS; 34 * let next BPF program in the cgroup chain or kernel 35 * handle it. 36 */ 37 return 1; 38 39 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) { 40 /* Not interested in SOL_SOCKET:SO_SNDBUF; 41 * let next BPF program in the cgroup chain or kernel 42 * handle it. 43 */ 44 return 1; 45 } 46 47 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) { 48 /* Not interested in SOL_TCP:TCP_CONGESTION; 49 * let next BPF program in the cgroup chain or kernel 50 * handle it. 51 */ 52 return 1; 53 } 54 55 if (ctx->level != SOL_CUSTOM) 56 return 0; /* EPERM, deny everything except custom level */ 57 58 if (optval + 1 > optval_end) 59 return 0; /* EPERM, bounds check */ 60 61 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0, 62 BPF_SK_STORAGE_GET_F_CREATE); 63 if (!storage) 64 return 0; /* EPERM, couldn't get sk storage */ 65 66 if (!ctx->retval) 67 return 0; /* EPERM, kernel should not have handled 68 * SOL_CUSTOM, something is wrong! 69 */ 70 ctx->retval = 0; /* Reset system call return value to zero */ 71 72 optval[0] = storage->val; 73 ctx->optlen = 1; 74 75 return 1; 76 } 77 78 SEC("cgroup/setsockopt") 79 int _setsockopt(struct bpf_sockopt *ctx) 80 { 81 __u8 *optval_end = ctx->optval_end; 82 __u8 *optval = ctx->optval; 83 struct sockopt_sk *storage; 84 85 if (ctx->level == SOL_IP && ctx->optname == IP_TOS) 86 /* Not interested in SOL_IP:IP_TOS; 87 * let next BPF program in the cgroup chain or kernel 88 * handle it. 89 */ 90 return 1; 91 92 if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) { 93 /* Overwrite SO_SNDBUF value */ 94 95 if (optval + sizeof(__u32) > optval_end) 96 return 0; /* EPERM, bounds check */ 97 98 *(__u32 *)optval = 0x55AA; 99 ctx->optlen = 4; 100 101 return 1; 102 } 103 104 if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) { 105 /* Always use cubic */ 106 107 if (optval + 5 > optval_end) 108 return 0; /* EPERM, bounds check */ 109 110 memcpy(optval, "cubic", 5); 111 ctx->optlen = 5; 112 113 return 1; 114 } 115 116 if (ctx->level != SOL_CUSTOM) 117 return 0; /* EPERM, deny everything except custom level */ 118 119 if (optval + 1 > optval_end) 120 return 0; /* EPERM, bounds check */ 121 122 storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0, 123 BPF_SK_STORAGE_GET_F_CREATE); 124 if (!storage) 125 return 0; /* EPERM, couldn't get sk storage */ 126 127 storage->val = optval[0]; 128 ctx->optlen = -1; /* BPF has consumed this option, don't call kernel 129 * setsockopt handler. 130 */ 131 132 return 1; 133 } 134