1 // SPDX-License-Identifier: BSD-3-Clause 2 /* 3 * Simple Landlock sandbox manager able to execute a process restricted by 4 * user-defined file system and network access control policies. 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 <linux/socket.h> 18 #include <stddef.h> 19 #include <stdio.h> 20 #include <stdlib.h> 21 #include <string.h> 22 #include <sys/prctl.h> 23 #include <sys/stat.h> 24 #include <sys/syscall.h> 25 #include <unistd.h> 26 #include <stdbool.h> 27 28 #ifndef landlock_create_ruleset 29 static inline int 30 landlock_create_ruleset(const struct landlock_ruleset_attr *const attr, 31 const size_t size, const __u32 flags) 32 { 33 return syscall(__NR_landlock_create_ruleset, attr, size, flags); 34 } 35 #endif 36 37 #ifndef landlock_add_rule 38 static inline int landlock_add_rule(const int ruleset_fd, 39 const enum landlock_rule_type rule_type, 40 const void *const rule_attr, 41 const __u32 flags) 42 { 43 return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr, 44 flags); 45 } 46 #endif 47 48 #ifndef landlock_restrict_self 49 static inline int landlock_restrict_self(const int ruleset_fd, 50 const __u32 flags) 51 { 52 return syscall(__NR_landlock_restrict_self, ruleset_fd, flags); 53 } 54 #endif 55 56 #define ENV_FS_RO_NAME "LL_FS_RO" 57 #define ENV_FS_RW_NAME "LL_FS_RW" 58 #define ENV_TCP_BIND_NAME "LL_TCP_BIND" 59 #define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" 60 #define ENV_SCOPED_NAME "LL_SCOPED" 61 #define ENV_DELIMITER ":" 62 63 static int parse_path(char *env_path, const char ***const path_list) 64 { 65 int i, num_paths = 0; 66 67 if (env_path) { 68 num_paths++; 69 for (i = 0; env_path[i]; i++) { 70 if (env_path[i] == ENV_DELIMITER[0]) 71 num_paths++; 72 } 73 } 74 *path_list = malloc(num_paths * sizeof(**path_list)); 75 for (i = 0; i < num_paths; i++) 76 (*path_list)[i] = strsep(&env_path, ENV_DELIMITER); 77 78 return num_paths; 79 } 80 81 /* clang-format off */ 82 83 #define ACCESS_FILE ( \ 84 LANDLOCK_ACCESS_FS_EXECUTE | \ 85 LANDLOCK_ACCESS_FS_WRITE_FILE | \ 86 LANDLOCK_ACCESS_FS_READ_FILE | \ 87 LANDLOCK_ACCESS_FS_TRUNCATE | \ 88 LANDLOCK_ACCESS_FS_IOCTL_DEV) 89 90 /* clang-format on */ 91 92 static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd, 93 const __u64 allowed_access) 94 { 95 int num_paths, i, ret = 1; 96 char *env_path_name; 97 const char **path_list = NULL; 98 struct landlock_path_beneath_attr path_beneath = { 99 .parent_fd = -1, 100 }; 101 102 env_path_name = getenv(env_var); 103 if (!env_path_name) { 104 /* Prevents users to forget a setting. */ 105 fprintf(stderr, "Missing environment variable %s\n", env_var); 106 return 1; 107 } 108 env_path_name = strdup(env_path_name); 109 unsetenv(env_var); 110 num_paths = parse_path(env_path_name, &path_list); 111 if (num_paths == 1 && path_list[0][0] == '\0') { 112 /* 113 * Allows to not use all possible restrictions (e.g. use 114 * LL_FS_RO without LL_FS_RW). 115 */ 116 ret = 0; 117 goto out_free_name; 118 } 119 120 for (i = 0; i < num_paths; i++) { 121 struct stat statbuf; 122 123 path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC); 124 if (path_beneath.parent_fd < 0) { 125 fprintf(stderr, "Failed to open \"%s\": %s\n", 126 path_list[i], strerror(errno)); 127 continue; 128 } 129 if (fstat(path_beneath.parent_fd, &statbuf)) { 130 fprintf(stderr, "Failed to stat \"%s\": %s\n", 131 path_list[i], strerror(errno)); 132 close(path_beneath.parent_fd); 133 goto out_free_name; 134 } 135 path_beneath.allowed_access = allowed_access; 136 if (!S_ISDIR(statbuf.st_mode)) 137 path_beneath.allowed_access &= ACCESS_FILE; 138 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH, 139 &path_beneath, 0)) { 140 fprintf(stderr, 141 "Failed to update the ruleset with \"%s\": %s\n", 142 path_list[i], strerror(errno)); 143 close(path_beneath.parent_fd); 144 goto out_free_name; 145 } 146 close(path_beneath.parent_fd); 147 } 148 ret = 0; 149 150 out_free_name: 151 free(path_list); 152 free(env_path_name); 153 return ret; 154 } 155 156 static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, 157 const __u64 allowed_access) 158 { 159 int ret = 1; 160 char *env_port_name, *env_port_name_next, *strport; 161 struct landlock_net_port_attr net_port = { 162 .allowed_access = allowed_access, 163 .port = 0, 164 }; 165 166 env_port_name = getenv(env_var); 167 if (!env_port_name) 168 return 0; 169 env_port_name = strdup(env_port_name); 170 unsetenv(env_var); 171 172 env_port_name_next = env_port_name; 173 while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) { 174 net_port.port = atoi(strport); 175 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT, 176 &net_port, 0)) { 177 fprintf(stderr, 178 "Failed to update the ruleset with port \"%llu\": %s\n", 179 net_port.port, strerror(errno)); 180 goto out_free_name; 181 } 182 } 183 ret = 0; 184 185 out_free_name: 186 free(env_port_name); 187 return ret; 188 } 189 190 /* Returns true on error, false otherwise. */ 191 static bool check_ruleset_scope(const char *const env_var, 192 struct landlock_ruleset_attr *ruleset_attr) 193 { 194 char *env_type_scope, *env_type_scope_next, *ipc_scoping_name; 195 bool error = false; 196 bool abstract_scoping = false; 197 bool signal_scoping = false; 198 199 /* Scoping is not supported by Landlock ABI */ 200 if (!(ruleset_attr->scoped & 201 (LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | LANDLOCK_SCOPE_SIGNAL))) 202 goto out_unset; 203 204 env_type_scope = getenv(env_var); 205 /* Scoping is not supported by the user */ 206 if (!env_type_scope || strcmp("", env_type_scope) == 0) 207 goto out_unset; 208 209 env_type_scope = strdup(env_type_scope); 210 env_type_scope_next = env_type_scope; 211 while ((ipc_scoping_name = 212 strsep(&env_type_scope_next, ENV_DELIMITER))) { 213 if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) { 214 abstract_scoping = true; 215 } else if (strcmp("s", ipc_scoping_name) == 0 && 216 !signal_scoping) { 217 signal_scoping = true; 218 } else { 219 fprintf(stderr, "Unknown or duplicate scope \"%s\"\n", 220 ipc_scoping_name); 221 error = true; 222 goto out_free_name; 223 } 224 } 225 226 out_free_name: 227 free(env_type_scope); 228 229 out_unset: 230 if (!abstract_scoping) 231 ruleset_attr->scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET; 232 if (!signal_scoping) 233 ruleset_attr->scoped &= ~LANDLOCK_SCOPE_SIGNAL; 234 235 unsetenv(env_var); 236 return error; 237 } 238 239 /* clang-format off */ 240 241 #define ACCESS_FS_ROUGHLY_READ ( \ 242 LANDLOCK_ACCESS_FS_EXECUTE | \ 243 LANDLOCK_ACCESS_FS_READ_FILE | \ 244 LANDLOCK_ACCESS_FS_READ_DIR) 245 246 #define ACCESS_FS_ROUGHLY_WRITE ( \ 247 LANDLOCK_ACCESS_FS_WRITE_FILE | \ 248 LANDLOCK_ACCESS_FS_REMOVE_DIR | \ 249 LANDLOCK_ACCESS_FS_REMOVE_FILE | \ 250 LANDLOCK_ACCESS_FS_MAKE_CHAR | \ 251 LANDLOCK_ACCESS_FS_MAKE_DIR | \ 252 LANDLOCK_ACCESS_FS_MAKE_REG | \ 253 LANDLOCK_ACCESS_FS_MAKE_SOCK | \ 254 LANDLOCK_ACCESS_FS_MAKE_FIFO | \ 255 LANDLOCK_ACCESS_FS_MAKE_BLOCK | \ 256 LANDLOCK_ACCESS_FS_MAKE_SYM | \ 257 LANDLOCK_ACCESS_FS_REFER | \ 258 LANDLOCK_ACCESS_FS_TRUNCATE | \ 259 LANDLOCK_ACCESS_FS_IOCTL_DEV) 260 261 /* clang-format on */ 262 263 #define LANDLOCK_ABI_LAST 6 264 265 int main(const int argc, char *const argv[], char *const *const envp) 266 { 267 const char *cmd_path; 268 char *const *cmd_argv; 269 int ruleset_fd, abi; 270 char *env_port_name; 271 __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ, 272 access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE; 273 274 struct landlock_ruleset_attr ruleset_attr = { 275 .handled_access_fs = access_fs_rw, 276 .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP | 277 LANDLOCK_ACCESS_NET_CONNECT_TCP, 278 .scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | 279 LANDLOCK_SCOPE_SIGNAL, 280 }; 281 282 if (argc < 2) { 283 fprintf(stderr, 284 "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s " 285 "<cmd> [args]...\n\n", 286 ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, 287 ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]); 288 fprintf(stderr, 289 "Execute a command in a restricted environment.\n\n"); 290 fprintf(stderr, 291 "Environment variables containing paths and ports " 292 "each separated by a colon:\n"); 293 fprintf(stderr, 294 "* %s: list of paths allowed to be used in a read-only way.\n", 295 ENV_FS_RO_NAME); 296 fprintf(stderr, 297 "* %s: list of paths allowed to be used in a read-write way.\n\n", 298 ENV_FS_RW_NAME); 299 fprintf(stderr, 300 "Environment variables containing ports are optional " 301 "and could be skipped.\n"); 302 fprintf(stderr, 303 "* %s: list of ports allowed to bind (server).\n", 304 ENV_TCP_BIND_NAME); 305 fprintf(stderr, 306 "* %s: list of ports allowed to connect (client).\n", 307 ENV_TCP_CONNECT_NAME); 308 fprintf(stderr, "* %s: list of scoped IPCs.\n", 309 ENV_SCOPED_NAME); 310 fprintf(stderr, 311 "\nexample:\n" 312 "%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" " 313 "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " 314 "%s=\"9418\" " 315 "%s=\"80:443\" " 316 "%s=\"a:s\" " 317 "%s bash -i\n\n", 318 ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, 319 ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]); 320 fprintf(stderr, 321 "This sandboxer can use Landlock features " 322 "up to ABI version %d.\n", 323 LANDLOCK_ABI_LAST); 324 return 1; 325 } 326 327 abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); 328 if (abi < 0) { 329 const int err = errno; 330 331 perror("Failed to check Landlock compatibility"); 332 switch (err) { 333 case ENOSYS: 334 fprintf(stderr, 335 "Hint: Landlock is not supported by the current kernel. " 336 "To support it, build the kernel with " 337 "CONFIG_SECURITY_LANDLOCK=y and prepend " 338 "\"landlock,\" to the content of CONFIG_LSM.\n"); 339 break; 340 case EOPNOTSUPP: 341 fprintf(stderr, 342 "Hint: Landlock is currently disabled. " 343 "It can be enabled in the kernel configuration by " 344 "prepending \"landlock,\" to the content of CONFIG_LSM, " 345 "or at boot time by setting the same content to the " 346 "\"lsm\" kernel parameter.\n"); 347 break; 348 } 349 return 1; 350 } 351 352 /* Best-effort security. */ 353 switch (abi) { 354 case 1: 355 /* 356 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 357 * 358 * Note: The "refer" operations (file renaming and linking 359 * across different directories) are always forbidden when using 360 * Landlock with ABI 1. 361 * 362 * If only ABI 1 is available, this sandboxer knowingly forbids 363 * refer operations. 364 * 365 * If a program *needs* to do refer operations after enabling 366 * Landlock, it can not use Landlock at ABI level 1. To be 367 * compatible with different kernel versions, such programs 368 * should then fall back to not restrict themselves at all if 369 * the running kernel only supports ABI 1. 370 */ 371 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; 372 __attribute__((fallthrough)); 373 case 2: 374 /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ 375 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; 376 __attribute__((fallthrough)); 377 case 3: 378 /* Removes network support for ABI < 4 */ 379 ruleset_attr.handled_access_net &= 380 ~(LANDLOCK_ACCESS_NET_BIND_TCP | 381 LANDLOCK_ACCESS_NET_CONNECT_TCP); 382 __attribute__((fallthrough)); 383 case 4: 384 /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */ 385 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV; 386 387 __attribute__((fallthrough)); 388 case 5: 389 /* Removes LANDLOCK_SCOPE_* for ABI < 6 */ 390 ruleset_attr.scoped &= ~(LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | 391 LANDLOCK_SCOPE_SIGNAL); 392 fprintf(stderr, 393 "Hint: You should update the running kernel " 394 "to leverage Landlock features " 395 "provided by ABI version %d (instead of %d).\n", 396 LANDLOCK_ABI_LAST, abi); 397 __attribute__((fallthrough)); 398 case LANDLOCK_ABI_LAST: 399 break; 400 default: 401 fprintf(stderr, 402 "Hint: You should update this sandboxer " 403 "to leverage Landlock features " 404 "provided by ABI version %d (instead of %d).\n", 405 abi, LANDLOCK_ABI_LAST); 406 } 407 access_fs_ro &= ruleset_attr.handled_access_fs; 408 access_fs_rw &= ruleset_attr.handled_access_fs; 409 410 /* Removes bind access attribute if not supported by a user. */ 411 env_port_name = getenv(ENV_TCP_BIND_NAME); 412 if (!env_port_name) { 413 ruleset_attr.handled_access_net &= 414 ~LANDLOCK_ACCESS_NET_BIND_TCP; 415 } 416 /* Removes connect access attribute if not supported by a user. */ 417 env_port_name = getenv(ENV_TCP_CONNECT_NAME); 418 if (!env_port_name) { 419 ruleset_attr.handled_access_net &= 420 ~LANDLOCK_ACCESS_NET_CONNECT_TCP; 421 } 422 423 if (check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr)) 424 return 1; 425 426 ruleset_fd = 427 landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); 428 if (ruleset_fd < 0) { 429 perror("Failed to create a ruleset"); 430 return 1; 431 } 432 433 if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) { 434 goto err_close_ruleset; 435 } 436 if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) { 437 goto err_close_ruleset; 438 } 439 440 if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd, 441 LANDLOCK_ACCESS_NET_BIND_TCP)) { 442 goto err_close_ruleset; 443 } 444 if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd, 445 LANDLOCK_ACCESS_NET_CONNECT_TCP)) { 446 goto err_close_ruleset; 447 } 448 449 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { 450 perror("Failed to restrict privileges"); 451 goto err_close_ruleset; 452 } 453 if (landlock_restrict_self(ruleset_fd, 0)) { 454 perror("Failed to enforce ruleset"); 455 goto err_close_ruleset; 456 } 457 close(ruleset_fd); 458 459 cmd_path = argv[1]; 460 cmd_argv = argv + 1; 461 fprintf(stderr, "Executing the sandboxed command...\n"); 462 execvpe(cmd_path, cmd_argv, envp); 463 fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path, 464 strerror(errno)); 465 fprintf(stderr, "Hint: access to the binary, the interpreter or " 466 "shared libraries may be denied.\n"); 467 return 1; 468 469 err_close_ruleset: 470 close(ruleset_fd); 471 return 1; 472 } 473