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1// SPDX-License-Identifier: BSD-3-Clause2/*3 * Simple Landlock sandbox manager able to execute a process restricted by4 * user-defined file system and network access control policies.5 *6 * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>7 * Copyright © 2020 ANSSI8 */9 10#define _GNU_SOURCE11#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_ruleset29static inline int30landlock_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#endif36 37#ifndef landlock_add_rule38static 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#endif47 48#ifndef landlock_restrict_self49static 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#endif55 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 63static 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 else77 *num_dst = num;78 79 return err;80}81 82static 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 111static 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. use133 * 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 169out_free_name:170 free(path_list);171 free(env_path_name);172 return ret;173}174 175static 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 213out_free_name:214 free(env_port_name);215 return ret;216}217 218/* Returns true on error, false otherwise. */219static 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 254out_free_name:255 free(env_type_scope);256 257out_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 6292 293#define XSTR(s) #s294#define STR(s) XSTR(s)295 296/* clang-format off */297 298static 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 331int 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 < 2383 *384 * Note: The "refer" operations (file renaming and linking385 * across different directories) are always forbidden when using386 * Landlock with ABI 1.387 *388 * If only ABI 1 is available, this sandboxer knowingly forbids389 * refer operations.390 *391 * If a program *needs* to do refer operations after enabling392 * Landlock, it can not use Landlock at ABI level 1. To be393 * compatible with different kernel versions, such programs394 * should then fall back to not restrict themselves at all if395 * 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 495err_close_ruleset:496 close(ruleset_fd);497 return 1;498}499