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 <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 continue; 124 } 125 if (fstat(path_beneath.parent_fd, &statbuf)) { 126 fprintf(stderr, "Failed to stat \"%s\": %s\n", 127 path_list[i], strerror(errno)); 128 close(path_beneath.parent_fd); 129 goto out_free_name; 130 } 131 path_beneath.allowed_access = allowed_access; 132 if (!S_ISDIR(statbuf.st_mode)) 133 path_beneath.allowed_access &= ACCESS_FILE; 134 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH, 135 &path_beneath, 0)) { 136 fprintf(stderr, 137 "Failed to update the ruleset with \"%s\": %s\n", 138 path_list[i], strerror(errno)); 139 close(path_beneath.parent_fd); 140 goto out_free_name; 141 } 142 close(path_beneath.parent_fd); 143 } 144 ret = 0; 145 146 out_free_name: 147 free(path_list); 148 free(env_path_name); 149 return ret; 150 } 151 152 static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, 153 const __u64 allowed_access) 154 { 155 int ret = 1; 156 char *env_port_name, *strport; 157 struct landlock_net_port_attr net_port = { 158 .allowed_access = allowed_access, 159 .port = 0, 160 }; 161 162 env_port_name = getenv(env_var); 163 if (!env_port_name) 164 return 0; 165 env_port_name = strdup(env_port_name); 166 unsetenv(env_var); 167 168 while ((strport = strsep(&env_port_name, ENV_DELIMITER))) { 169 net_port.port = atoi(strport); 170 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT, 171 &net_port, 0)) { 172 fprintf(stderr, 173 "Failed to update the ruleset with port \"%llu\": %s\n", 174 net_port.port, strerror(errno)); 175 goto out_free_name; 176 } 177 } 178 ret = 0; 179 180 out_free_name: 181 free(env_port_name); 182 return ret; 183 } 184 185 /* clang-format off */ 186 187 #define ACCESS_FS_ROUGHLY_READ ( \ 188 LANDLOCK_ACCESS_FS_EXECUTE | \ 189 LANDLOCK_ACCESS_FS_READ_FILE | \ 190 LANDLOCK_ACCESS_FS_READ_DIR) 191 192 #define ACCESS_FS_ROUGHLY_WRITE ( \ 193 LANDLOCK_ACCESS_FS_WRITE_FILE | \ 194 LANDLOCK_ACCESS_FS_REMOVE_DIR | \ 195 LANDLOCK_ACCESS_FS_REMOVE_FILE | \ 196 LANDLOCK_ACCESS_FS_MAKE_CHAR | \ 197 LANDLOCK_ACCESS_FS_MAKE_DIR | \ 198 LANDLOCK_ACCESS_FS_MAKE_REG | \ 199 LANDLOCK_ACCESS_FS_MAKE_SOCK | \ 200 LANDLOCK_ACCESS_FS_MAKE_FIFO | \ 201 LANDLOCK_ACCESS_FS_MAKE_BLOCK | \ 202 LANDLOCK_ACCESS_FS_MAKE_SYM | \ 203 LANDLOCK_ACCESS_FS_REFER | \ 204 LANDLOCK_ACCESS_FS_TRUNCATE) 205 206 /* clang-format on */ 207 208 #define LANDLOCK_ABI_LAST 4 209 210 int main(const int argc, char *const argv[], char *const *const envp) 211 { 212 const char *cmd_path; 213 char *const *cmd_argv; 214 int ruleset_fd, abi; 215 char *env_port_name; 216 __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ, 217 access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE; 218 219 struct landlock_ruleset_attr ruleset_attr = { 220 .handled_access_fs = access_fs_rw, 221 .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP | 222 LANDLOCK_ACCESS_NET_CONNECT_TCP, 223 }; 224 225 if (argc < 2) { 226 fprintf(stderr, 227 "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s " 228 "<cmd> [args]...\n\n", 229 ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, 230 ENV_TCP_CONNECT_NAME, argv[0]); 231 fprintf(stderr, 232 "Execute a command in a restricted environment.\n\n"); 233 fprintf(stderr, 234 "Environment variables containing paths and ports " 235 "each separated by a colon:\n"); 236 fprintf(stderr, 237 "* %s: list of paths allowed to be used in a read-only way.\n", 238 ENV_FS_RO_NAME); 239 fprintf(stderr, 240 "* %s: list of paths allowed to be used in a read-write way.\n\n", 241 ENV_FS_RW_NAME); 242 fprintf(stderr, 243 "Environment variables containing ports are optional " 244 "and could be skipped.\n"); 245 fprintf(stderr, 246 "* %s: list of ports allowed to bind (server).\n", 247 ENV_TCP_BIND_NAME); 248 fprintf(stderr, 249 "* %s: list of ports allowed to connect (client).\n", 250 ENV_TCP_CONNECT_NAME); 251 fprintf(stderr, 252 "\nexample:\n" 253 "%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" " 254 "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " 255 "%s=\"9418\" " 256 "%s=\"80:443\" " 257 "%s bash -i\n\n", 258 ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, 259 ENV_TCP_CONNECT_NAME, argv[0]); 260 fprintf(stderr, 261 "This sandboxer can use Landlock features " 262 "up to ABI version %d.\n", 263 LANDLOCK_ABI_LAST); 264 return 1; 265 } 266 267 abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); 268 if (abi < 0) { 269 const int err = errno; 270 271 perror("Failed to check Landlock compatibility"); 272 switch (err) { 273 case ENOSYS: 274 fprintf(stderr, 275 "Hint: Landlock is not supported by the current kernel. " 276 "To support it, build the kernel with " 277 "CONFIG_SECURITY_LANDLOCK=y and prepend " 278 "\"landlock,\" to the content of CONFIG_LSM.\n"); 279 break; 280 case EOPNOTSUPP: 281 fprintf(stderr, 282 "Hint: Landlock is currently disabled. " 283 "It can be enabled in the kernel configuration by " 284 "prepending \"landlock,\" to the content of CONFIG_LSM, " 285 "or at boot time by setting the same content to the " 286 "\"lsm\" kernel parameter.\n"); 287 break; 288 } 289 return 1; 290 } 291 292 /* Best-effort security. */ 293 switch (abi) { 294 case 1: 295 /* 296 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 297 * 298 * Note: The "refer" operations (file renaming and linking 299 * across different directories) are always forbidden when using 300 * Landlock with ABI 1. 301 * 302 * If only ABI 1 is available, this sandboxer knowingly forbids 303 * refer operations. 304 * 305 * If a program *needs* to do refer operations after enabling 306 * Landlock, it can not use Landlock at ABI level 1. To be 307 * compatible with different kernel versions, such programs 308 * should then fall back to not restrict themselves at all if 309 * the running kernel only supports ABI 1. 310 */ 311 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; 312 __attribute__((fallthrough)); 313 case 2: 314 /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ 315 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; 316 __attribute__((fallthrough)); 317 case 3: 318 /* Removes network support for ABI < 4 */ 319 ruleset_attr.handled_access_net &= 320 ~(LANDLOCK_ACCESS_NET_BIND_TCP | 321 LANDLOCK_ACCESS_NET_CONNECT_TCP); 322 fprintf(stderr, 323 "Hint: You should update the running kernel " 324 "to leverage Landlock features " 325 "provided by ABI version %d (instead of %d).\n", 326 LANDLOCK_ABI_LAST, abi); 327 __attribute__((fallthrough)); 328 case LANDLOCK_ABI_LAST: 329 break; 330 default: 331 fprintf(stderr, 332 "Hint: You should update this sandboxer " 333 "to leverage Landlock features " 334 "provided by ABI version %d (instead of %d).\n", 335 abi, LANDLOCK_ABI_LAST); 336 } 337 access_fs_ro &= ruleset_attr.handled_access_fs; 338 access_fs_rw &= ruleset_attr.handled_access_fs; 339 340 /* Removes bind access attribute if not supported by a user. */ 341 env_port_name = getenv(ENV_TCP_BIND_NAME); 342 if (!env_port_name) { 343 ruleset_attr.handled_access_net &= 344 ~LANDLOCK_ACCESS_NET_BIND_TCP; 345 } 346 /* Removes connect access attribute if not supported by a user. */ 347 env_port_name = getenv(ENV_TCP_CONNECT_NAME); 348 if (!env_port_name) { 349 ruleset_attr.handled_access_net &= 350 ~LANDLOCK_ACCESS_NET_CONNECT_TCP; 351 } 352 353 ruleset_fd = 354 landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); 355 if (ruleset_fd < 0) { 356 perror("Failed to create a ruleset"); 357 return 1; 358 } 359 360 if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) { 361 goto err_close_ruleset; 362 } 363 if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) { 364 goto err_close_ruleset; 365 } 366 367 if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd, 368 LANDLOCK_ACCESS_NET_BIND_TCP)) { 369 goto err_close_ruleset; 370 } 371 if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd, 372 LANDLOCK_ACCESS_NET_CONNECT_TCP)) { 373 goto err_close_ruleset; 374 } 375 376 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { 377 perror("Failed to restrict privileges"); 378 goto err_close_ruleset; 379 } 380 if (landlock_restrict_self(ruleset_fd, 0)) { 381 perror("Failed to enforce ruleset"); 382 goto err_close_ruleset; 383 } 384 close(ruleset_fd); 385 386 cmd_path = argv[1]; 387 cmd_argv = argv + 1; 388 fprintf(stderr, "Executing the sandboxed command...\n"); 389 execvpe(cmd_path, cmd_argv, envp); 390 fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path, 391 strerror(errno)); 392 fprintf(stderr, "Hint: access to the binary, the interpreter or " 393 "shared libraries may be denied.\n"); 394 return 1; 395 396 err_close_ruleset: 397 close(ruleset_fd); 398 return 1; 399 } 400