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/socket.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 #include <stdbool.h> 26 27 #if defined(__GLIBC__) 28 #include <linux/prctl.h> 29 #endif 30 31 #ifndef landlock_create_ruleset 32 static inline int 33 landlock_create_ruleset(const struct landlock_ruleset_attr *const attr, 34 const size_t size, const __u32 flags) 35 { 36 return syscall(__NR_landlock_create_ruleset, attr, size, flags); 37 } 38 #endif 39 40 #ifndef landlock_add_rule 41 static inline int landlock_add_rule(const int ruleset_fd, 42 const enum landlock_rule_type rule_type, 43 const void *const rule_attr, 44 const __u32 flags) 45 { 46 return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr, 47 flags); 48 } 49 #endif 50 51 #ifndef landlock_restrict_self 52 static inline int landlock_restrict_self(const int ruleset_fd, 53 const __u32 flags) 54 { 55 return syscall(__NR_landlock_restrict_self, ruleset_fd, flags); 56 } 57 #endif 58 59 #define ENV_FS_RO_NAME "LL_FS_RO" 60 #define ENV_FS_RW_NAME "LL_FS_RW" 61 #define ENV_TCP_BIND_NAME "LL_TCP_BIND" 62 #define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" 63 #define ENV_SCOPED_NAME "LL_SCOPED" 64 #define ENV_FORCE_LOG_NAME "LL_FORCE_LOG" 65 #define ENV_DELIMITER ":" 66 67 static int str2num(const char *numstr, __u64 *num_dst) 68 { 69 char *endptr = NULL; 70 int err = 0; 71 __u64 num; 72 73 errno = 0; 74 num = strtoull(numstr, &endptr, 10); 75 if (errno != 0) 76 err = errno; 77 /* Was the string empty, or not entirely parsed successfully? */ 78 else if ((*numstr == '\0') || (*endptr != '\0')) 79 err = EINVAL; 80 else 81 *num_dst = num; 82 83 return err; 84 } 85 86 static int parse_path(char *env_path, const char ***const path_list) 87 { 88 int i, num_paths = 0; 89 90 if (env_path) { 91 num_paths++; 92 for (i = 0; env_path[i]; i++) { 93 if (env_path[i] == ENV_DELIMITER[0]) 94 num_paths++; 95 } 96 } 97 *path_list = malloc(num_paths * sizeof(**path_list)); 98 if (!*path_list) 99 return -1; 100 101 for (i = 0; i < num_paths; i++) 102 (*path_list)[i] = strsep(&env_path, ENV_DELIMITER); 103 104 return num_paths; 105 } 106 107 /* clang-format off */ 108 109 #define ACCESS_FILE ( \ 110 LANDLOCK_ACCESS_FS_EXECUTE | \ 111 LANDLOCK_ACCESS_FS_WRITE_FILE | \ 112 LANDLOCK_ACCESS_FS_READ_FILE | \ 113 LANDLOCK_ACCESS_FS_TRUNCATE | \ 114 LANDLOCK_ACCESS_FS_IOCTL_DEV | \ 115 LANDLOCK_ACCESS_FS_RESOLVE_UNIX) 116 117 /* clang-format on */ 118 119 static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd, 120 const __u64 allowed_access) 121 { 122 int num_paths, i, ret = 1; 123 char *env_path_name; 124 const char **path_list = NULL; 125 struct landlock_path_beneath_attr path_beneath = { 126 .parent_fd = -1, 127 }; 128 129 env_path_name = getenv(env_var); 130 if (!env_path_name) { 131 /* Prevents users to forget a setting. */ 132 fprintf(stderr, "Missing environment variable %s\n", env_var); 133 return 1; 134 } 135 env_path_name = strdup(env_path_name); 136 unsetenv(env_var); 137 num_paths = parse_path(env_path_name, &path_list); 138 if (num_paths < 0) { 139 fprintf(stderr, "Failed to allocate memory\n"); 140 goto out_free_name; 141 } 142 if (num_paths == 1 && path_list[0][0] == '\0') { 143 /* 144 * Allows to not use all possible restrictions (e.g. use 145 * LL_FS_RO without LL_FS_RW). 146 */ 147 ret = 0; 148 goto out_free_name; 149 } 150 151 for (i = 0; i < num_paths; i++) { 152 struct stat statbuf; 153 154 path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC); 155 if (path_beneath.parent_fd < 0) { 156 fprintf(stderr, "Failed to open \"%s\": %s\n", 157 path_list[i], strerror(errno)); 158 continue; 159 } 160 if (fstat(path_beneath.parent_fd, &statbuf)) { 161 fprintf(stderr, "Failed to stat \"%s\": %s\n", 162 path_list[i], strerror(errno)); 163 close(path_beneath.parent_fd); 164 goto out_free_name; 165 } 166 path_beneath.allowed_access = allowed_access; 167 if (!S_ISDIR(statbuf.st_mode)) 168 path_beneath.allowed_access &= ACCESS_FILE; 169 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH, 170 &path_beneath, 0)) { 171 fprintf(stderr, 172 "Failed to update the ruleset with \"%s\": %s\n", 173 path_list[i], strerror(errno)); 174 close(path_beneath.parent_fd); 175 goto out_free_name; 176 } 177 close(path_beneath.parent_fd); 178 } 179 ret = 0; 180 181 out_free_name: 182 free(path_list); 183 free(env_path_name); 184 return ret; 185 } 186 187 static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, 188 const __u64 allowed_access) 189 { 190 int ret = 1; 191 char *env_port_name, *env_port_name_next, *strport; 192 struct landlock_net_port_attr net_port = { 193 .allowed_access = allowed_access, 194 }; 195 196 env_port_name = getenv(env_var); 197 if (!env_port_name) 198 return 0; 199 env_port_name = strdup(env_port_name); 200 unsetenv(env_var); 201 202 env_port_name_next = env_port_name; 203 while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) { 204 __u64 port; 205 206 if (strcmp(strport, "") == 0) 207 continue; 208 209 if (str2num(strport, &port)) { 210 fprintf(stderr, "Failed to parse port at \"%s\"\n", 211 strport); 212 goto out_free_name; 213 } 214 net_port.port = port; 215 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT, 216 &net_port, 0)) { 217 fprintf(stderr, 218 "Failed to update the ruleset with port \"%llu\": %s\n", 219 net_port.port, strerror(errno)); 220 goto out_free_name; 221 } 222 } 223 ret = 0; 224 225 out_free_name: 226 free(env_port_name); 227 return ret; 228 } 229 230 /* Returns true on error, false otherwise. */ 231 static bool check_ruleset_scope(const char *const env_var, 232 struct landlock_ruleset_attr *ruleset_attr) 233 { 234 char *env_type_scope, *env_type_scope_next, *ipc_scoping_name; 235 bool error = false; 236 bool abstract_scoping = false; 237 bool signal_scoping = false; 238 239 /* Scoping is not supported by Landlock ABI */ 240 if (!(ruleset_attr->scoped & 241 (LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | LANDLOCK_SCOPE_SIGNAL))) 242 goto out_unset; 243 244 env_type_scope = getenv(env_var); 245 /* Scoping is not supported by the user */ 246 if (!env_type_scope || strcmp("", env_type_scope) == 0) 247 goto out_unset; 248 249 env_type_scope = strdup(env_type_scope); 250 env_type_scope_next = env_type_scope; 251 while ((ipc_scoping_name = 252 strsep(&env_type_scope_next, ENV_DELIMITER))) { 253 if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) { 254 abstract_scoping = true; 255 } else if (strcmp("s", ipc_scoping_name) == 0 && 256 !signal_scoping) { 257 signal_scoping = true; 258 } else { 259 fprintf(stderr, "Unknown or duplicate scope \"%s\"\n", 260 ipc_scoping_name); 261 error = true; 262 goto out_free_name; 263 } 264 } 265 266 out_free_name: 267 free(env_type_scope); 268 269 out_unset: 270 if (!abstract_scoping) 271 ruleset_attr->scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET; 272 if (!signal_scoping) 273 ruleset_attr->scoped &= ~LANDLOCK_SCOPE_SIGNAL; 274 275 unsetenv(env_var); 276 return error; 277 } 278 279 /* clang-format off */ 280 281 #define ACCESS_FS_ROUGHLY_READ ( \ 282 LANDLOCK_ACCESS_FS_EXECUTE | \ 283 LANDLOCK_ACCESS_FS_READ_FILE | \ 284 LANDLOCK_ACCESS_FS_READ_DIR) 285 286 #define ACCESS_FS_ROUGHLY_WRITE ( \ 287 LANDLOCK_ACCESS_FS_WRITE_FILE | \ 288 LANDLOCK_ACCESS_FS_REMOVE_DIR | \ 289 LANDLOCK_ACCESS_FS_REMOVE_FILE | \ 290 LANDLOCK_ACCESS_FS_MAKE_CHAR | \ 291 LANDLOCK_ACCESS_FS_MAKE_DIR | \ 292 LANDLOCK_ACCESS_FS_MAKE_REG | \ 293 LANDLOCK_ACCESS_FS_MAKE_SOCK | \ 294 LANDLOCK_ACCESS_FS_MAKE_FIFO | \ 295 LANDLOCK_ACCESS_FS_MAKE_BLOCK | \ 296 LANDLOCK_ACCESS_FS_MAKE_SYM | \ 297 LANDLOCK_ACCESS_FS_REFER | \ 298 LANDLOCK_ACCESS_FS_TRUNCATE | \ 299 LANDLOCK_ACCESS_FS_IOCTL_DEV | \ 300 LANDLOCK_ACCESS_FS_RESOLVE_UNIX) 301 302 /* clang-format on */ 303 304 #define LANDLOCK_ABI_LAST 9 305 306 #define XSTR(s) #s 307 #define STR(s) XSTR(s) 308 309 /* clang-format off */ 310 311 static const char help[] = 312 "usage: " ENV_FS_RO_NAME "=\"...\" " ENV_FS_RW_NAME "=\"...\" " 313 "[other environment variables] %1$s <cmd> [args]...\n" 314 "\n" 315 "Execute the given command in a restricted environment.\n" 316 "Multi-valued settings (lists of ports, paths, scopes) are colon-delimited.\n" 317 "\n" 318 "Mandatory settings:\n" 319 "* " ENV_FS_RO_NAME ": paths allowed to be used in a read-only way\n" 320 "* " ENV_FS_RW_NAME ": paths allowed to be used in a read-write way\n" 321 "\n" 322 "Optional settings (when not set, their associated access check " 323 "is always allowed, which is different from an empty string which " 324 "means an empty list):\n" 325 "* " ENV_TCP_BIND_NAME ": ports allowed to bind (server)\n" 326 "* " ENV_TCP_CONNECT_NAME ": ports allowed to connect (client)\n" 327 "* " ENV_SCOPED_NAME ": actions denied on the outside of the landlock domain\n" 328 " - \"a\" to restrict opening abstract unix sockets\n" 329 " - \"s\" to restrict sending signals\n" 330 "\n" 331 "A sandboxer should not log denied access requests to avoid spamming logs, " 332 "but to test audit we can set " ENV_FORCE_LOG_NAME "=1\n" 333 "\n" 334 "Example:\n" 335 ENV_FS_RO_NAME "=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" " 336 ENV_FS_RW_NAME "=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " 337 ENV_TCP_BIND_NAME "=\"9418\" " 338 ENV_TCP_CONNECT_NAME "=\"80:443\" " 339 ENV_SCOPED_NAME "=\"a:s\" " 340 "%1$s bash -i\n" 341 "\n" 342 "This sandboxer can use Landlock features up to ABI version " 343 STR(LANDLOCK_ABI_LAST) ".\n"; 344 345 /* clang-format on */ 346 347 int main(const int argc, char *const argv[], char *const *const envp) 348 { 349 const char *cmd_path; 350 char *const *cmd_argv; 351 int ruleset_fd, abi; 352 char *env_port_name, *env_force_log; 353 __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ, 354 access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE; 355 356 struct landlock_ruleset_attr ruleset_attr = { 357 .handled_access_fs = access_fs_rw, 358 .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP | 359 LANDLOCK_ACCESS_NET_CONNECT_TCP, 360 .scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | 361 LANDLOCK_SCOPE_SIGNAL, 362 }; 363 int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON; 364 int set_restrict_flags = 0; 365 366 if (argc < 2) { 367 fprintf(stderr, help, argv[0]); 368 return 1; 369 } 370 371 abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); 372 if (abi < 0) { 373 const int err = errno; 374 375 perror("Failed to check Landlock compatibility"); 376 switch (err) { 377 case ENOSYS: 378 fprintf(stderr, 379 "Hint: Landlock is not supported by the current kernel. " 380 "To support it, build the kernel with " 381 "CONFIG_SECURITY_LANDLOCK=y and prepend " 382 "\"landlock,\" to the content of CONFIG_LSM.\n"); 383 break; 384 case EOPNOTSUPP: 385 fprintf(stderr, 386 "Hint: Landlock is currently disabled. " 387 "It can be enabled in the kernel configuration by " 388 "prepending \"landlock,\" to the content of CONFIG_LSM, " 389 "or at boot time by setting the same content to the " 390 "\"lsm\" kernel parameter.\n"); 391 break; 392 } 393 return 1; 394 } 395 396 /* Best-effort security. */ 397 switch (abi) { 398 case 1: 399 /* 400 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 401 * 402 * Note: The "refer" operations (file renaming and linking 403 * across different directories) are always forbidden when using 404 * Landlock with ABI 1. 405 * 406 * If only ABI 1 is available, this sandboxer knowingly forbids 407 * refer operations. 408 * 409 * If a program *needs* to do refer operations after enabling 410 * Landlock, it can not use Landlock at ABI level 1. To be 411 * compatible with different kernel versions, such programs 412 * should then fall back to not restrict themselves at all if 413 * the running kernel only supports ABI 1. 414 */ 415 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; 416 __attribute__((fallthrough)); 417 case 2: 418 /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ 419 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; 420 __attribute__((fallthrough)); 421 case 3: 422 /* Removes network support for ABI < 4 */ 423 ruleset_attr.handled_access_net &= 424 ~(LANDLOCK_ACCESS_NET_BIND_TCP | 425 LANDLOCK_ACCESS_NET_CONNECT_TCP); 426 __attribute__((fallthrough)); 427 case 4: 428 /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */ 429 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV; 430 431 __attribute__((fallthrough)); 432 case 5: 433 /* Removes LANDLOCK_SCOPE_* for ABI < 6 */ 434 ruleset_attr.scoped &= ~(LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | 435 LANDLOCK_SCOPE_SIGNAL); 436 __attribute__((fallthrough)); 437 case 6: 438 /* Removes LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON for ABI < 7 */ 439 supported_restrict_flags &= 440 ~LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON; 441 __attribute__((fallthrough)); 442 case 7: 443 case 8: 444 /* Removes LANDLOCK_ACCESS_FS_RESOLVE_UNIX for ABI < 9 */ 445 ruleset_attr.handled_access_fs &= 446 ~LANDLOCK_ACCESS_FS_RESOLVE_UNIX; 447 /* Must be printed for any ABI < LANDLOCK_ABI_LAST. */ 448 fprintf(stderr, 449 "Hint: You should update the running kernel " 450 "to leverage Landlock features " 451 "provided by ABI version %d (instead of %d).\n", 452 LANDLOCK_ABI_LAST, abi); 453 __attribute__((fallthrough)); 454 case LANDLOCK_ABI_LAST: 455 break; 456 default: 457 fprintf(stderr, 458 "Hint: You should update this sandboxer " 459 "to leverage Landlock features " 460 "provided by ABI version %d (instead of %d).\n", 461 abi, LANDLOCK_ABI_LAST); 462 } 463 access_fs_ro &= ruleset_attr.handled_access_fs; 464 access_fs_rw &= ruleset_attr.handled_access_fs; 465 466 /* Removes bind access attribute if not supported by a user. */ 467 env_port_name = getenv(ENV_TCP_BIND_NAME); 468 if (!env_port_name) { 469 ruleset_attr.handled_access_net &= 470 ~LANDLOCK_ACCESS_NET_BIND_TCP; 471 } 472 /* Removes connect access attribute if not supported by a user. */ 473 env_port_name = getenv(ENV_TCP_CONNECT_NAME); 474 if (!env_port_name) { 475 ruleset_attr.handled_access_net &= 476 ~LANDLOCK_ACCESS_NET_CONNECT_TCP; 477 } 478 479 if (check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr)) 480 return 1; 481 482 /* Enables optional logs. */ 483 env_force_log = getenv(ENV_FORCE_LOG_NAME); 484 if (env_force_log) { 485 if (strcmp(env_force_log, "1") != 0) { 486 fprintf(stderr, "Unknown value for " ENV_FORCE_LOG_NAME 487 " (only \"1\" is handled)\n"); 488 return 1; 489 } 490 if (!(supported_restrict_flags & 491 LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON)) { 492 fprintf(stderr, 493 "Audit logs not supported by current kernel\n"); 494 return 1; 495 } 496 set_restrict_flags |= LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON; 497 unsetenv(ENV_FORCE_LOG_NAME); 498 } 499 500 ruleset_fd = 501 landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); 502 if (ruleset_fd < 0) { 503 perror("Failed to create a ruleset"); 504 return 1; 505 } 506 507 if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) { 508 goto err_close_ruleset; 509 } 510 if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) { 511 goto err_close_ruleset; 512 } 513 514 if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd, 515 LANDLOCK_ACCESS_NET_BIND_TCP)) { 516 goto err_close_ruleset; 517 } 518 if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd, 519 LANDLOCK_ACCESS_NET_CONNECT_TCP)) { 520 goto err_close_ruleset; 521 } 522 523 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { 524 perror("Failed to restrict privileges"); 525 goto err_close_ruleset; 526 } 527 if (landlock_restrict_self(ruleset_fd, set_restrict_flags)) { 528 perror("Failed to enforce ruleset"); 529 goto err_close_ruleset; 530 } 531 close(ruleset_fd); 532 533 cmd_path = argv[1]; 534 cmd_argv = argv + 1; 535 fprintf(stderr, "Executing the sandboxed command...\n"); 536 execvpe(cmd_path, cmd_argv, envp); 537 fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path, 538 strerror(errno)); 539 fprintf(stderr, "Hint: access to the binary, the interpreter or " 540 "shared libraries may be denied.\n"); 541 return 1; 542 543 err_close_ruleset: 544 close(ruleset_fd); 545 return 1; 546 } 547