1 // SPDX-License-Identifier: BSD-3-Clause 2 /* 3 * Simple Landlock sandbox manager able to launch a process restricted by a 4 * user-defined filesystem access control policy. 5 * 6 * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net> 7 * Copyright © 2020 ANSSI 8 */ 9 10 #define _GNU_SOURCE 11 #define __SANE_USERSPACE_TYPES__ 12 #include <arpa/inet.h> 13 #include <errno.h> 14 #include <fcntl.h> 15 #include <linux/landlock.h> 16 #include <linux/prctl.h> 17 #include <stddef.h> 18 #include <stdio.h> 19 #include <stdlib.h> 20 #include <string.h> 21 #include <sys/prctl.h> 22 #include <sys/stat.h> 23 #include <sys/syscall.h> 24 #include <unistd.h> 25 26 #ifndef landlock_create_ruleset 27 static inline int 28 landlock_create_ruleset(const struct landlock_ruleset_attr *const attr, 29 const size_t size, const __u32 flags) 30 { 31 return syscall(__NR_landlock_create_ruleset, attr, size, flags); 32 } 33 #endif 34 35 #ifndef landlock_add_rule 36 static inline int landlock_add_rule(const int ruleset_fd, 37 const enum landlock_rule_type rule_type, 38 const void *const rule_attr, 39 const __u32 flags) 40 { 41 return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr, 42 flags); 43 } 44 #endif 45 46 #ifndef landlock_restrict_self 47 static inline int landlock_restrict_self(const int ruleset_fd, 48 const __u32 flags) 49 { 50 return syscall(__NR_landlock_restrict_self, ruleset_fd, flags); 51 } 52 #endif 53 54 #define ENV_FS_RO_NAME "LL_FS_RO" 55 #define ENV_FS_RW_NAME "LL_FS_RW" 56 #define ENV_TCP_BIND_NAME "LL_TCP_BIND" 57 #define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" 58 #define ENV_DELIMITER ":" 59 60 static int parse_path(char *env_path, const char ***const path_list) 61 { 62 int i, num_paths = 0; 63 64 if (env_path) { 65 num_paths++; 66 for (i = 0; env_path[i]; i++) { 67 if (env_path[i] == ENV_DELIMITER[0]) 68 num_paths++; 69 } 70 } 71 *path_list = malloc(num_paths * sizeof(**path_list)); 72 for (i = 0; i < num_paths; i++) 73 (*path_list)[i] = strsep(&env_path, ENV_DELIMITER); 74 75 return num_paths; 76 } 77 78 /* clang-format off */ 79 80 #define ACCESS_FILE ( \ 81 LANDLOCK_ACCESS_FS_EXECUTE | \ 82 LANDLOCK_ACCESS_FS_WRITE_FILE | \ 83 LANDLOCK_ACCESS_FS_READ_FILE | \ 84 LANDLOCK_ACCESS_FS_TRUNCATE) 85 86 /* clang-format on */ 87 88 static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd, 89 const __u64 allowed_access) 90 { 91 int num_paths, i, ret = 1; 92 char *env_path_name; 93 const char **path_list = NULL; 94 struct landlock_path_beneath_attr path_beneath = { 95 .parent_fd = -1, 96 }; 97 98 env_path_name = getenv(env_var); 99 if (!env_path_name) { 100 /* Prevents users to forget a setting. */ 101 fprintf(stderr, "Missing environment variable %s\n", env_var); 102 return 1; 103 } 104 env_path_name = strdup(env_path_name); 105 unsetenv(env_var); 106 num_paths = parse_path(env_path_name, &path_list); 107 if (num_paths == 1 && path_list[0][0] == '\0') { 108 /* 109 * Allows to not use all possible restrictions (e.g. use 110 * LL_FS_RO without LL_FS_RW). 111 */ 112 ret = 0; 113 goto out_free_name; 114 } 115 116 for (i = 0; i < num_paths; i++) { 117 struct stat statbuf; 118 119 path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC); 120 if (path_beneath.parent_fd < 0) { 121 fprintf(stderr, "Failed to open \"%s\": %s\n", 122 path_list[i], strerror(errno)); 123 goto out_free_name; 124 } 125 if (fstat(path_beneath.parent_fd, &statbuf)) { 126 close(path_beneath.parent_fd); 127 goto out_free_name; 128 } 129 path_beneath.allowed_access = allowed_access; 130 if (!S_ISDIR(statbuf.st_mode)) 131 path_beneath.allowed_access &= ACCESS_FILE; 132 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH, 133 &path_beneath, 0)) { 134 fprintf(stderr, 135 "Failed to update the ruleset with \"%s\": %s\n", 136 path_list[i], strerror(errno)); 137 close(path_beneath.parent_fd); 138 goto out_free_name; 139 } 140 close(path_beneath.parent_fd); 141 } 142 ret = 0; 143 144 out_free_name: 145 free(path_list); 146 free(env_path_name); 147 return ret; 148 } 149 150 static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, 151 const __u64 allowed_access) 152 { 153 int ret = 1; 154 char *env_port_name, *strport; 155 struct landlock_net_port_attr net_port = { 156 .allowed_access = allowed_access, 157 .port = 0, 158 }; 159 160 env_port_name = getenv(env_var); 161 if (!env_port_name) 162 return 0; 163 env_port_name = strdup(env_port_name); 164 unsetenv(env_var); 165 166 while ((strport = strsep(&env_port_name, ENV_DELIMITER))) { 167 net_port.port = atoi(strport); 168 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT, 169 &net_port, 0)) { 170 fprintf(stderr, 171 "Failed to update the ruleset with port \"%llu\": %s\n", 172 net_port.port, strerror(errno)); 173 goto out_free_name; 174 } 175 } 176 ret = 0; 177 178 out_free_name: 179 free(env_port_name); 180 return ret; 181 } 182 183 /* clang-format off */ 184 185 #define ACCESS_FS_ROUGHLY_READ ( \ 186 LANDLOCK_ACCESS_FS_EXECUTE | \ 187 LANDLOCK_ACCESS_FS_READ_FILE | \ 188 LANDLOCK_ACCESS_FS_READ_DIR) 189 190 #define ACCESS_FS_ROUGHLY_WRITE ( \ 191 LANDLOCK_ACCESS_FS_WRITE_FILE | \ 192 LANDLOCK_ACCESS_FS_REMOVE_DIR | \ 193 LANDLOCK_ACCESS_FS_REMOVE_FILE | \ 194 LANDLOCK_ACCESS_FS_MAKE_CHAR | \ 195 LANDLOCK_ACCESS_FS_MAKE_DIR | \ 196 LANDLOCK_ACCESS_FS_MAKE_REG | \ 197 LANDLOCK_ACCESS_FS_MAKE_SOCK | \ 198 LANDLOCK_ACCESS_FS_MAKE_FIFO | \ 199 LANDLOCK_ACCESS_FS_MAKE_BLOCK | \ 200 LANDLOCK_ACCESS_FS_MAKE_SYM | \ 201 LANDLOCK_ACCESS_FS_REFER | \ 202 LANDLOCK_ACCESS_FS_TRUNCATE) 203 204 /* clang-format on */ 205 206 #define LANDLOCK_ABI_LAST 4 207 208 int main(const int argc, char *const argv[], char *const *const envp) 209 { 210 const char *cmd_path; 211 char *const *cmd_argv; 212 int ruleset_fd, abi; 213 char *env_port_name; 214 __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ, 215 access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE; 216 217 struct landlock_ruleset_attr ruleset_attr = { 218 .handled_access_fs = access_fs_rw, 219 .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP | 220 LANDLOCK_ACCESS_NET_CONNECT_TCP, 221 }; 222 223 if (argc < 2) { 224 fprintf(stderr, 225 "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s " 226 "<cmd> [args]...\n\n", 227 ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, 228 ENV_TCP_CONNECT_NAME, argv[0]); 229 fprintf(stderr, 230 "Launch a command in a restricted environment.\n\n"); 231 fprintf(stderr, 232 "Environment variables containing paths and ports " 233 "each separated by a colon:\n"); 234 fprintf(stderr, 235 "* %s: list of paths allowed to be used in a read-only way.\n", 236 ENV_FS_RO_NAME); 237 fprintf(stderr, 238 "* %s: list of paths allowed to be used in a read-write way.\n\n", 239 ENV_FS_RW_NAME); 240 fprintf(stderr, 241 "Environment variables containing ports are optional " 242 "and could be skipped.\n"); 243 fprintf(stderr, 244 "* %s: list of ports allowed to bind (server).\n", 245 ENV_TCP_BIND_NAME); 246 fprintf(stderr, 247 "* %s: list of ports allowed to connect (client).\n", 248 ENV_TCP_CONNECT_NAME); 249 fprintf(stderr, 250 "\nexample:\n" 251 "%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" " 252 "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " 253 "%s=\"9418\" " 254 "%s=\"80:443\" " 255 "%s bash -i\n\n", 256 ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, 257 ENV_TCP_CONNECT_NAME, argv[0]); 258 fprintf(stderr, 259 "This sandboxer can use Landlock features " 260 "up to ABI version %d.\n", 261 LANDLOCK_ABI_LAST); 262 return 1; 263 } 264 265 abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); 266 if (abi < 0) { 267 const int err = errno; 268 269 perror("Failed to check Landlock compatibility"); 270 switch (err) { 271 case ENOSYS: 272 fprintf(stderr, 273 "Hint: Landlock is not supported by the current kernel. " 274 "To support it, build the kernel with " 275 "CONFIG_SECURITY_LANDLOCK=y and prepend " 276 "\"landlock,\" to the content of CONFIG_LSM.\n"); 277 break; 278 case EOPNOTSUPP: 279 fprintf(stderr, 280 "Hint: Landlock is currently disabled. " 281 "It can be enabled in the kernel configuration by " 282 "prepending \"landlock,\" to the content of CONFIG_LSM, " 283 "or at boot time by setting the same content to the " 284 "\"lsm\" kernel parameter.\n"); 285 break; 286 } 287 return 1; 288 } 289 290 /* Best-effort security. */ 291 switch (abi) { 292 case 1: 293 /* 294 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 295 * 296 * Note: The "refer" operations (file renaming and linking 297 * across different directories) are always forbidden when using 298 * Landlock with ABI 1. 299 * 300 * If only ABI 1 is available, this sandboxer knowingly forbids 301 * refer operations. 302 * 303 * If a program *needs* to do refer operations after enabling 304 * Landlock, it can not use Landlock at ABI level 1. To be 305 * compatible with different kernel versions, such programs 306 * should then fall back to not restrict themselves at all if 307 * the running kernel only supports ABI 1. 308 */ 309 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; 310 __attribute__((fallthrough)); 311 case 2: 312 /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ 313 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; 314 __attribute__((fallthrough)); 315 case 3: 316 /* Removes network support for ABI < 4 */ 317 ruleset_attr.handled_access_net &= 318 ~(LANDLOCK_ACCESS_NET_BIND_TCP | 319 LANDLOCK_ACCESS_NET_CONNECT_TCP); 320 fprintf(stderr, 321 "Hint: You should update the running kernel " 322 "to leverage Landlock features " 323 "provided by ABI version %d (instead of %d).\n", 324 LANDLOCK_ABI_LAST, abi); 325 __attribute__((fallthrough)); 326 case LANDLOCK_ABI_LAST: 327 break; 328 default: 329 fprintf(stderr, 330 "Hint: You should update this sandboxer " 331 "to leverage Landlock features " 332 "provided by ABI version %d (instead of %d).\n", 333 abi, LANDLOCK_ABI_LAST); 334 } 335 access_fs_ro &= ruleset_attr.handled_access_fs; 336 access_fs_rw &= ruleset_attr.handled_access_fs; 337 338 /* Removes bind access attribute if not supported by a user. */ 339 env_port_name = getenv(ENV_TCP_BIND_NAME); 340 if (!env_port_name) { 341 ruleset_attr.handled_access_net &= 342 ~LANDLOCK_ACCESS_NET_BIND_TCP; 343 } 344 /* Removes connect access attribute if not supported by a user. */ 345 env_port_name = getenv(ENV_TCP_CONNECT_NAME); 346 if (!env_port_name) { 347 ruleset_attr.handled_access_net &= 348 ~LANDLOCK_ACCESS_NET_CONNECT_TCP; 349 } 350 351 ruleset_fd = 352 landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); 353 if (ruleset_fd < 0) { 354 perror("Failed to create a ruleset"); 355 return 1; 356 } 357 358 if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) { 359 goto err_close_ruleset; 360 } 361 if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) { 362 goto err_close_ruleset; 363 } 364 365 if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd, 366 LANDLOCK_ACCESS_NET_BIND_TCP)) { 367 goto err_close_ruleset; 368 } 369 if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd, 370 LANDLOCK_ACCESS_NET_CONNECT_TCP)) { 371 goto err_close_ruleset; 372 } 373 374 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { 375 perror("Failed to restrict privileges"); 376 goto err_close_ruleset; 377 } 378 if (landlock_restrict_self(ruleset_fd, 0)) { 379 perror("Failed to enforce ruleset"); 380 goto err_close_ruleset; 381 } 382 close(ruleset_fd); 383 384 cmd_path = argv[1]; 385 cmd_argv = argv + 1; 386 execvpe(cmd_path, cmd_argv, envp); 387 fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path, 388 strerror(errno)); 389 fprintf(stderr, "Hint: access to the binary, the interpreter or " 390 "shared libraries may be denied.\n"); 391 return 1; 392 393 err_close_ruleset: 394 close(ruleset_fd); 395 return 1; 396 } 397