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