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 Micka��l Sala��n <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 27static inline int 28landlock_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 36static 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 47static 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 60static 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 LANDLOCK_ACCESS_FS_IOCTL_DEV) 86 87/* clang-format on */ 88 89static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd, 90 const __u64 allowed_access) 91{ 92 int num_paths, i, ret = 1; 93 char *env_path_name; 94 const char **path_list = NULL; 95 struct landlock_path_beneath_attr path_beneath = { 96 .parent_fd = -1, 97 }; 98 99 env_path_name = getenv(env_var); 100 if (!env_path_name) { 101 /* Prevents users to forget a setting. */ 102 fprintf(stderr, "Missing environment variable %s\n", env_var); 103 return 1; 104 } 105 env_path_name = strdup(env_path_name); 106 unsetenv(env_var); 107 num_paths = parse_path(env_path_name, &path_list); 108 if (num_paths == 1 && path_list[0][0] == '\0') { 109 /* 110 * Allows to not use all possible restrictions (e.g. use 111 * LL_FS_RO without LL_FS_RW). 112 */ 113 ret = 0; 114 goto out_free_name; 115 } 116 117 for (i = 0; i < num_paths; i++) { 118 struct stat statbuf; 119 120 path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC); 121 if (path_beneath.parent_fd < 0) { 122 fprintf(stderr, "Failed to open \"%s\": %s\n", 123 path_list[i], strerror(errno)); 124 continue; 125 } 126 if (fstat(path_beneath.parent_fd, &statbuf)) { 127 fprintf(stderr, "Failed to stat \"%s\": %s\n", 128 path_list[i], strerror(errno)); 129 close(path_beneath.parent_fd); 130 goto out_free_name; 131 } 132 path_beneath.allowed_access = allowed_access; 133 if (!S_ISDIR(statbuf.st_mode)) 134 path_beneath.allowed_access &= ACCESS_FILE; 135 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH, 136 &path_beneath, 0)) { 137 fprintf(stderr, 138 "Failed to update the ruleset with \"%s\": %s\n", 139 path_list[i], strerror(errno)); 140 close(path_beneath.parent_fd); 141 goto out_free_name; 142 } 143 close(path_beneath.parent_fd); 144 } 145 ret = 0; 146 147out_free_name: 148 free(path_list); 149 free(env_path_name); 150 return ret; 151} 152 153static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, 154 const __u64 allowed_access) 155{ 156 int ret = 1; 157 char *env_port_name, *env_port_name_next, *strport; 158 struct landlock_net_port_attr net_port = { 159 .allowed_access = allowed_access, 160 .port = 0, 161 }; 162 163 env_port_name = getenv(env_var); 164 if (!env_port_name) 165 return 0; 166 env_port_name = strdup(env_port_name); 167 unsetenv(env_var); 168 169 env_port_name_next = env_port_name; 170 while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) { 171 net_port.port = atoi(strport); 172 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT, 173 &net_port, 0)) { 174 fprintf(stderr, 175 "Failed to update the ruleset with port \"%llu\": %s\n", 176 net_port.port, strerror(errno)); 177 goto out_free_name; 178 } 179 } 180 ret = 0; 181 182out_free_name: 183 free(env_port_name); 184 return ret; 185} 186 187/* clang-format off */ 188 189#define ACCESS_FS_ROUGHLY_READ ( \ 190 LANDLOCK_ACCESS_FS_EXECUTE | \ 191 LANDLOCK_ACCESS_FS_READ_FILE | \ 192 LANDLOCK_ACCESS_FS_READ_DIR) 193 194#define ACCESS_FS_ROUGHLY_WRITE ( \ 195 LANDLOCK_ACCESS_FS_WRITE_FILE | \ 196 LANDLOCK_ACCESS_FS_REMOVE_DIR | \ 197 LANDLOCK_ACCESS_FS_REMOVE_FILE | \ 198 LANDLOCK_ACCESS_FS_MAKE_CHAR | \ 199 LANDLOCK_ACCESS_FS_MAKE_DIR | \ 200 LANDLOCK_ACCESS_FS_MAKE_REG | \ 201 LANDLOCK_ACCESS_FS_MAKE_SOCK | \ 202 LANDLOCK_ACCESS_FS_MAKE_FIFO | \ 203 LANDLOCK_ACCESS_FS_MAKE_BLOCK | \ 204 LANDLOCK_ACCESS_FS_MAKE_SYM | \ 205 LANDLOCK_ACCESS_FS_REFER | \ 206 LANDLOCK_ACCESS_FS_TRUNCATE | \ 207 LANDLOCK_ACCESS_FS_IOCTL_DEV) 208 209/* clang-format on */ 210 211#define LANDLOCK_ABI_LAST 5 212 213int main(const int argc, char *const argv[], char *const *const envp) 214{ 215 const char *cmd_path; 216 char *const *cmd_argv; 217 int ruleset_fd, abi; 218 char *env_port_name; 219 __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ, 220 access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE; 221 222 struct landlock_ruleset_attr ruleset_attr = { 223 .handled_access_fs = access_fs_rw, 224 .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP | 225 LANDLOCK_ACCESS_NET_CONNECT_TCP, 226 }; 227 228 if (argc < 2) { 229 fprintf(stderr, 230 "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s " 231 "<cmd> [args]...\n\n", 232 ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, 233 ENV_TCP_CONNECT_NAME, argv[0]); 234 fprintf(stderr, 235 "Execute a command in a restricted environment.\n\n"); 236 fprintf(stderr, 237 "Environment variables containing paths and ports " 238 "each separated by a colon:\n"); 239 fprintf(stderr, 240 "* %s: list of paths allowed to be used in a read-only way.\n", 241 ENV_FS_RO_NAME); 242 fprintf(stderr, 243 "* %s: list of paths allowed to be used in a read-write way.\n\n", 244 ENV_FS_RW_NAME); 245 fprintf(stderr, 246 "Environment variables containing ports are optional " 247 "and could be skipped.\n"); 248 fprintf(stderr, 249 "* %s: list of ports allowed to bind (server).\n", 250 ENV_TCP_BIND_NAME); 251 fprintf(stderr, 252 "* %s: list of ports allowed to connect (client).\n", 253 ENV_TCP_CONNECT_NAME); 254 fprintf(stderr, 255 "\nexample:\n" 256 "%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" " 257 "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " 258 "%s=\"9418\" " 259 "%s=\"80:443\" " 260 "%s bash -i\n\n", 261 ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, 262 ENV_TCP_CONNECT_NAME, argv[0]); 263 fprintf(stderr, 264 "This sandboxer can use Landlock features " 265 "up to ABI version %d.\n", 266 LANDLOCK_ABI_LAST); 267 return 1; 268 } 269 270 abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); 271 if (abi < 0) { 272 const int err = errno; 273 274 perror("Failed to check Landlock compatibility"); 275 switch (err) { 276 case ENOSYS: 277 fprintf(stderr, 278 "Hint: Landlock is not supported by the current kernel. " 279 "To support it, build the kernel with " 280 "CONFIG_SECURITY_LANDLOCK=y and prepend " 281 "\"landlock,\" to the content of CONFIG_LSM.\n"); 282 break; 283 case EOPNOTSUPP: 284 fprintf(stderr, 285 "Hint: Landlock is currently disabled. " 286 "It can be enabled in the kernel configuration by " 287 "prepending \"landlock,\" to the content of CONFIG_LSM, " 288 "or at boot time by setting the same content to the " 289 "\"lsm\" kernel parameter.\n"); 290 break; 291 } 292 return 1; 293 } 294 295 /* Best-effort security. */ 296 switch (abi) { 297 case 1: 298 /* 299 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 300 * 301 * Note: The "refer" operations (file renaming and linking 302 * across different directories) are always forbidden when using 303 * Landlock with ABI 1. 304 * 305 * If only ABI 1 is available, this sandboxer knowingly forbids 306 * refer operations. 307 * 308 * If a program *needs* to do refer operations after enabling 309 * Landlock, it can not use Landlock at ABI level 1. To be 310 * compatible with different kernel versions, such programs 311 * should then fall back to not restrict themselves at all if 312 * the running kernel only supports ABI 1. 313 */ 314 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; 315 __attribute__((fallthrough)); 316 case 2: 317 /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ 318 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; 319 __attribute__((fallthrough)); 320 case 3: 321 /* Removes network support for ABI < 4 */ 322 ruleset_attr.handled_access_net &= 323 ~(LANDLOCK_ACCESS_NET_BIND_TCP | 324 LANDLOCK_ACCESS_NET_CONNECT_TCP); 325 __attribute__((fallthrough)); 326 case 4: 327 /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */ 328 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV; 329 330 fprintf(stderr, 331 "Hint: You should update the running kernel " 332 "to leverage Landlock features " 333 "provided by ABI version %d (instead of %d).\n", 334 LANDLOCK_ABI_LAST, abi); 335 __attribute__((fallthrough)); 336 case LANDLOCK_ABI_LAST: 337 break; 338 default: 339 fprintf(stderr, 340 "Hint: You should update this sandboxer " 341 "to leverage Landlock features " 342 "provided by ABI version %d (instead of %d).\n", 343 abi, LANDLOCK_ABI_LAST); 344 } 345 access_fs_ro &= ruleset_attr.handled_access_fs; 346 access_fs_rw &= ruleset_attr.handled_access_fs; 347 348 /* Removes bind access attribute if not supported by a user. */ 349 env_port_name = getenv(ENV_TCP_BIND_NAME); 350 if (!env_port_name) { 351 ruleset_attr.handled_access_net &= 352 ~LANDLOCK_ACCESS_NET_BIND_TCP; 353 } 354 /* Removes connect access attribute if not supported by a user. */ 355 env_port_name = getenv(ENV_TCP_CONNECT_NAME); 356 if (!env_port_name) { 357 ruleset_attr.handled_access_net &= 358 ~LANDLOCK_ACCESS_NET_CONNECT_TCP; 359 } 360 361 ruleset_fd = 362 landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); 363 if (ruleset_fd < 0) { 364 perror("Failed to create a ruleset"); 365 return 1; 366 } 367 368 if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) { 369 goto err_close_ruleset; 370 } 371 if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) { 372 goto err_close_ruleset; 373 } 374 375 if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd, 376 LANDLOCK_ACCESS_NET_BIND_TCP)) { 377 goto err_close_ruleset; 378 } 379 if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd, 380 LANDLOCK_ACCESS_NET_CONNECT_TCP)) { 381 goto err_close_ruleset; 382 } 383 384 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { 385 perror("Failed to restrict privileges"); 386 goto err_close_ruleset; 387 } 388 if (landlock_restrict_self(ruleset_fd, 0)) { 389 perror("Failed to enforce ruleset"); 390 goto err_close_ruleset; 391 } 392 close(ruleset_fd); 393 394 cmd_path = argv[1]; 395 cmd_argv = argv + 1; 396 fprintf(stderr, "Executing the sandboxed command...\n"); 397 execvpe(cmd_path, cmd_argv, envp); 398 fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path, 399 strerror(errno)); 400 fprintf(stderr, "Hint: access to the binary, the interpreter or " 401 "shared libraries may be denied.\n"); 402 return 1; 403 404err_close_ruleset: 405 close(ruleset_fd); 406 return 1; 407} 408