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