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/socket.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#include <stdbool.h>
26
27#if defined(__GLIBC__)
28#include <linux/prctl.h>
29#endif
30
31#ifndef landlock_create_ruleset
32static inline int
33landlock_create_ruleset(const struct landlock_ruleset_attr *const attr,
34 const size_t size, const __u32 flags)
35{
36 return syscall(__NR_landlock_create_ruleset, attr, size, flags);
37}
38#endif
39
40#ifndef landlock_add_rule
41static inline int landlock_add_rule(const int ruleset_fd,
42 const enum landlock_rule_type rule_type,
43 const void *const rule_attr,
44 const __u32 flags)
45{
46 return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr,
47 flags);
48}
49#endif
50
51#ifndef landlock_restrict_self
52static inline int landlock_restrict_self(const int ruleset_fd,
53 const __u32 flags)
54{
55 return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
56}
57#endif
58
59#define ENV_FS_RO_NAME "LL_FS_RO"
60#define ENV_FS_RW_NAME "LL_FS_RW"
61#define ENV_TCP_BIND_NAME "LL_TCP_BIND"
62#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
63#define ENV_SCOPED_NAME "LL_SCOPED"
64#define ENV_FORCE_LOG_NAME "LL_FORCE_LOG"
65#define ENV_DELIMITER ":"
66
67static int str2num(const char *numstr, __u64 *num_dst)
68{
69 char *endptr = NULL;
70 int err = 0;
71 __u64 num;
72
73 errno = 0;
74 num = strtoull(numstr, &endptr, 10);
75 if (errno != 0)
76 err = errno;
77 /* Was the string empty, or not entirely parsed successfully? */
78 else if ((*numstr == '\0') || (*endptr != '\0'))
79 err = EINVAL;
80 else
81 *num_dst = num;
82
83 return err;
84}
85
86static int parse_path(char *env_path, const char ***const path_list)
87{
88 int i, num_paths = 0;
89
90 if (env_path) {
91 num_paths++;
92 for (i = 0; env_path[i]; i++) {
93 if (env_path[i] == ENV_DELIMITER[0])
94 num_paths++;
95 }
96 }
97 *path_list = malloc(num_paths * sizeof(**path_list));
98 if (!*path_list)
99 return -1;
100
101 for (i = 0; i < num_paths; i++)
102 (*path_list)[i] = strsep(&env_path, ENV_DELIMITER);
103
104 return num_paths;
105}
106
107/* clang-format off */
108
109#define ACCESS_FILE ( \
110 LANDLOCK_ACCESS_FS_EXECUTE | \
111 LANDLOCK_ACCESS_FS_WRITE_FILE | \
112 LANDLOCK_ACCESS_FS_READ_FILE | \
113 LANDLOCK_ACCESS_FS_TRUNCATE | \
114 LANDLOCK_ACCESS_FS_IOCTL_DEV)
115
116/* clang-format on */
117
118static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
119 const __u64 allowed_access)
120{
121 int num_paths, i, ret = 1;
122 char *env_path_name;
123 const char **path_list = NULL;
124 struct landlock_path_beneath_attr path_beneath = {
125 .parent_fd = -1,
126 };
127
128 env_path_name = getenv(env_var);
129 if (!env_path_name) {
130 /* Prevents users to forget a setting. */
131 fprintf(stderr, "Missing environment variable %s\n", env_var);
132 return 1;
133 }
134 env_path_name = strdup(env_path_name);
135 unsetenv(env_var);
136 num_paths = parse_path(env_path: env_path_name, path_list: &path_list);
137 if (num_paths < 0) {
138 fprintf(stderr, "Failed to allocate memory\n");
139 goto out_free_name;
140 }
141 if (num_paths == 1 && path_list[0][0] == '\0') {
142 /*
143 * Allows to not use all possible restrictions (e.g. use
144 * LL_FS_RO without LL_FS_RW).
145 */
146 ret = 0;
147 goto out_free_name;
148 }
149
150 for (i = 0; i < num_paths; i++) {
151 struct stat statbuf;
152
153 path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC);
154 if (path_beneath.parent_fd < 0) {
155 fprintf(stderr, "Failed to open \"%s\": %s\n",
156 path_list[i], strerror(errno));
157 continue;
158 }
159 if (fstat(path_beneath.parent_fd, &statbuf)) {
160 fprintf(stderr, "Failed to stat \"%s\": %s\n",
161 path_list[i], strerror(errno));
162 close(path_beneath.parent_fd);
163 goto out_free_name;
164 }
165 path_beneath.allowed_access = allowed_access;
166 if (!S_ISDIR(statbuf.st_mode))
167 path_beneath.allowed_access &= ACCESS_FILE;
168 if (landlock_add_rule(ruleset_fd, rule_type: LANDLOCK_RULE_PATH_BENEATH,
169 rule_attr: &path_beneath, flags: 0)) {
170 fprintf(stderr,
171 "Failed to update the ruleset with \"%s\": %s\n",
172 path_list[i], strerror(errno));
173 close(path_beneath.parent_fd);
174 goto out_free_name;
175 }
176 close(path_beneath.parent_fd);
177 }
178 ret = 0;
179
180out_free_name:
181 free(path_list);
182 free(env_path_name);
183 return ret;
184}
185
186static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
187 const __u64 allowed_access)
188{
189 int ret = 1;
190 char *env_port_name, *env_port_name_next, *strport;
191 struct landlock_net_port_attr net_port = {
192 .allowed_access = allowed_access,
193 };
194
195 env_port_name = getenv(env_var);
196 if (!env_port_name)
197 return 0;
198 env_port_name = strdup(env_port_name);
199 unsetenv(env_var);
200
201 env_port_name_next = env_port_name;
202 while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) {
203 __u64 port;
204
205 if (strcmp(strport, "") == 0)
206 continue;
207
208 if (str2num(numstr: strport, num_dst: &port)) {
209 fprintf(stderr, "Failed to parse port at \"%s\"\n",
210 strport);
211 goto out_free_name;
212 }
213 net_port.port = port;
214 if (landlock_add_rule(ruleset_fd, rule_type: LANDLOCK_RULE_NET_PORT,
215 rule_attr: &net_port, flags: 0)) {
216 fprintf(stderr,
217 "Failed to update the ruleset with port \"%llu\": %s\n",
218 net_port.port, strerror(errno));
219 goto out_free_name;
220 }
221 }
222 ret = 0;
223
224out_free_name:
225 free(env_port_name);
226 return ret;
227}
228
229/* Returns true on error, false otherwise. */
230static bool check_ruleset_scope(const char *const env_var,
231 struct landlock_ruleset_attr *ruleset_attr)
232{
233 char *env_type_scope, *env_type_scope_next, *ipc_scoping_name;
234 bool error = false;
235 bool abstract_scoping = false;
236 bool signal_scoping = false;
237
238 /* Scoping is not supported by Landlock ABI */
239 if (!(ruleset_attr->scoped &
240 (LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | LANDLOCK_SCOPE_SIGNAL)))
241 goto out_unset;
242
243 env_type_scope = getenv(env_var);
244 /* Scoping is not supported by the user */
245 if (!env_type_scope || strcmp("", env_type_scope) == 0)
246 goto out_unset;
247
248 env_type_scope = strdup(env_type_scope);
249 env_type_scope_next = env_type_scope;
250 while ((ipc_scoping_name =
251 strsep(&env_type_scope_next, ENV_DELIMITER))) {
252 if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) {
253 abstract_scoping = true;
254 } else if (strcmp("s", ipc_scoping_name) == 0 &&
255 !signal_scoping) {
256 signal_scoping = true;
257 } else {
258 fprintf(stderr, "Unknown or duplicate scope \"%s\"\n",
259 ipc_scoping_name);
260 error = true;
261 goto out_free_name;
262 }
263 }
264
265out_free_name:
266 free(env_type_scope);
267
268out_unset:
269 if (!abstract_scoping)
270 ruleset_attr->scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET;
271 if (!signal_scoping)
272 ruleset_attr->scoped &= ~LANDLOCK_SCOPE_SIGNAL;
273
274 unsetenv(env_var);
275 return error;
276}
277
278/* clang-format off */
279
280#define ACCESS_FS_ROUGHLY_READ ( \
281 LANDLOCK_ACCESS_FS_EXECUTE | \
282 LANDLOCK_ACCESS_FS_READ_FILE | \
283 LANDLOCK_ACCESS_FS_READ_DIR)
284
285#define ACCESS_FS_ROUGHLY_WRITE ( \
286 LANDLOCK_ACCESS_FS_WRITE_FILE | \
287 LANDLOCK_ACCESS_FS_REMOVE_DIR | \
288 LANDLOCK_ACCESS_FS_REMOVE_FILE | \
289 LANDLOCK_ACCESS_FS_MAKE_CHAR | \
290 LANDLOCK_ACCESS_FS_MAKE_DIR | \
291 LANDLOCK_ACCESS_FS_MAKE_REG | \
292 LANDLOCK_ACCESS_FS_MAKE_SOCK | \
293 LANDLOCK_ACCESS_FS_MAKE_FIFO | \
294 LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
295 LANDLOCK_ACCESS_FS_MAKE_SYM | \
296 LANDLOCK_ACCESS_FS_REFER | \
297 LANDLOCK_ACCESS_FS_TRUNCATE | \
298 LANDLOCK_ACCESS_FS_IOCTL_DEV)
299
300/* clang-format on */
301
302#define LANDLOCK_ABI_LAST 7
303
304#define XSTR(s) #s
305#define STR(s) XSTR(s)
306
307/* clang-format off */
308
309static const char help[] =
310 "usage: " ENV_FS_RO_NAME "=\"...\" " ENV_FS_RW_NAME "=\"...\" "
311 "[other environment variables] %1$s <cmd> [args]...\n"
312 "\n"
313 "Execute the given command in a restricted environment.\n"
314 "Multi-valued settings (lists of ports, paths, scopes) are colon-delimited.\n"
315 "\n"
316 "Mandatory settings:\n"
317 "* " ENV_FS_RO_NAME ": paths allowed to be used in a read-only way\n"
318 "* " ENV_FS_RW_NAME ": paths allowed to be used in a read-write way\n"
319 "\n"
320 "Optional settings (when not set, their associated access check "
321 "is always allowed, which is different from an empty string which "
322 "means an empty list):\n"
323 "* " ENV_TCP_BIND_NAME ": ports allowed to bind (server)\n"
324 "* " ENV_TCP_CONNECT_NAME ": ports allowed to connect (client)\n"
325 "* " ENV_SCOPED_NAME ": actions denied on the outside of the landlock domain\n"
326 " - \"a\" to restrict opening abstract unix sockets\n"
327 " - \"s\" to restrict sending signals\n"
328 "\n"
329 "A sandboxer should not log denied access requests to avoid spamming logs, "
330 "but to test audit we can set " ENV_FORCE_LOG_NAME "=1\n"
331 "\n"
332 "Example:\n"
333 ENV_FS_RO_NAME "=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
334 ENV_FS_RW_NAME "=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
335 ENV_TCP_BIND_NAME "=\"9418\" "
336 ENV_TCP_CONNECT_NAME "=\"80:443\" "
337 ENV_SCOPED_NAME "=\"a:s\" "
338 "%1$s bash -i\n"
339 "\n"
340 "This sandboxer can use Landlock features up to ABI version "
341 STR(LANDLOCK_ABI_LAST) ".\n";
342
343/* clang-format on */
344
345int main(const int argc, char *const argv[], char *const *const envp)
346{
347 const char *cmd_path;
348 char *const *cmd_argv;
349 int ruleset_fd, abi;
350 char *env_port_name, *env_force_log;
351 __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
352 access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
353
354 struct landlock_ruleset_attr ruleset_attr = {
355 .handled_access_fs = access_fs_rw,
356 .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP |
357 LANDLOCK_ACCESS_NET_CONNECT_TCP,
358 .scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
359 LANDLOCK_SCOPE_SIGNAL,
360 };
361 int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
362 int set_restrict_flags = 0;
363
364 if (argc < 2) {
365 fprintf(stderr, help, argv[0]);
366 return 1;
367 }
368
369 abi = landlock_create_ruleset(NULL, size: 0, LANDLOCK_CREATE_RULESET_VERSION);
370 if (abi < 0) {
371 const int err = errno;
372
373 perror("Failed to check Landlock compatibility");
374 switch (err) {
375 case ENOSYS:
376 fprintf(stderr,
377 "Hint: Landlock is not supported by the current kernel. "
378 "To support it, build the kernel with "
379 "CONFIG_SECURITY_LANDLOCK=y and prepend "
380 "\"landlock,\" to the content of CONFIG_LSM.\n");
381 break;
382 case EOPNOTSUPP:
383 fprintf(stderr,
384 "Hint: Landlock is currently disabled. "
385 "It can be enabled in the kernel configuration by "
386 "prepending \"landlock,\" to the content of CONFIG_LSM, "
387 "or at boot time by setting the same content to the "
388 "\"lsm\" kernel parameter.\n");
389 break;
390 }
391 return 1;
392 }
393
394 /* Best-effort security. */
395 switch (abi) {
396 case 1:
397 /*
398 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2
399 *
400 * Note: The "refer" operations (file renaming and linking
401 * across different directories) are always forbidden when using
402 * Landlock with ABI 1.
403 *
404 * If only ABI 1 is available, this sandboxer knowingly forbids
405 * refer operations.
406 *
407 * If a program *needs* to do refer operations after enabling
408 * Landlock, it can not use Landlock at ABI level 1. To be
409 * compatible with different kernel versions, such programs
410 * should then fall back to not restrict themselves at all if
411 * the running kernel only supports ABI 1.
412 */
413 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
414 __attribute__((fallthrough));
415 case 2:
416 /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
417 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
418 __attribute__((fallthrough));
419 case 3:
420 /* Removes network support for ABI < 4 */
421 ruleset_attr.handled_access_net &=
422 ~(LANDLOCK_ACCESS_NET_BIND_TCP |
423 LANDLOCK_ACCESS_NET_CONNECT_TCP);
424 __attribute__((fallthrough));
425 case 4:
426 /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */
427 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV;
428
429 __attribute__((fallthrough));
430 case 5:
431 /* Removes LANDLOCK_SCOPE_* for ABI < 6 */
432 ruleset_attr.scoped &= ~(LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
433 LANDLOCK_SCOPE_SIGNAL);
434 __attribute__((fallthrough));
435 case 6:
436 /* Removes LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON for ABI < 7 */
437 supported_restrict_flags &=
438 ~LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
439
440 /* Must be printed for any ABI < LANDLOCK_ABI_LAST. */
441 fprintf(stderr,
442 "Hint: You should update the running kernel "
443 "to leverage Landlock features "
444 "provided by ABI version %d (instead of %d).\n",
445 LANDLOCK_ABI_LAST, abi);
446 __attribute__((fallthrough));
447 case LANDLOCK_ABI_LAST:
448 break;
449 default:
450 fprintf(stderr,
451 "Hint: You should update this sandboxer "
452 "to leverage Landlock features "
453 "provided by ABI version %d (instead of %d).\n",
454 abi, LANDLOCK_ABI_LAST);
455 }
456 access_fs_ro &= ruleset_attr.handled_access_fs;
457 access_fs_rw &= ruleset_attr.handled_access_fs;
458
459 /* Removes bind access attribute if not supported by a user. */
460 env_port_name = getenv(ENV_TCP_BIND_NAME);
461 if (!env_port_name) {
462 ruleset_attr.handled_access_net &=
463 ~LANDLOCK_ACCESS_NET_BIND_TCP;
464 }
465 /* Removes connect access attribute if not supported by a user. */
466 env_port_name = getenv(ENV_TCP_CONNECT_NAME);
467 if (!env_port_name) {
468 ruleset_attr.handled_access_net &=
469 ~LANDLOCK_ACCESS_NET_CONNECT_TCP;
470 }
471
472 if (check_ruleset_scope(ENV_SCOPED_NAME, ruleset_attr: &ruleset_attr))
473 return 1;
474
475 /* Enables optional logs. */
476 env_force_log = getenv(ENV_FORCE_LOG_NAME);
477 if (env_force_log) {
478 if (strcmp(env_force_log, "1") != 0) {
479 fprintf(stderr, "Unknown value for " ENV_FORCE_LOG_NAME
480 " (only \"1\" is handled)\n");
481 return 1;
482 }
483 if (!(supported_restrict_flags &
484 LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON)) {
485 fprintf(stderr,
486 "Audit logs not supported by current kernel\n");
487 return 1;
488 }
489 set_restrict_flags |= LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
490 unsetenv(ENV_FORCE_LOG_NAME);
491 }
492
493 ruleset_fd =
494 landlock_create_ruleset(attr: &ruleset_attr, size: sizeof(ruleset_attr), flags: 0);
495 if (ruleset_fd < 0) {
496 perror("Failed to create a ruleset");
497 return 1;
498 }
499
500 if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, allowed_access: access_fs_ro)) {
501 goto err_close_ruleset;
502 }
503 if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, allowed_access: access_fs_rw)) {
504 goto err_close_ruleset;
505 }
506
507 if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
508 LANDLOCK_ACCESS_NET_BIND_TCP)) {
509 goto err_close_ruleset;
510 }
511 if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd,
512 LANDLOCK_ACCESS_NET_CONNECT_TCP)) {
513 goto err_close_ruleset;
514 }
515
516 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
517 perror("Failed to restrict privileges");
518 goto err_close_ruleset;
519 }
520 if (landlock_restrict_self(ruleset_fd, flags: set_restrict_flags)) {
521 perror("Failed to enforce ruleset");
522 goto err_close_ruleset;
523 }
524 close(ruleset_fd);
525
526 cmd_path = argv[1];
527 cmd_argv = argv + 1;
528 fprintf(stderr, "Executing the sandboxed command...\n");
529 execvpe(cmd_path, cmd_argv, envp);
530 fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
531 strerror(errno));
532 fprintf(stderr, "Hint: access to the binary, the interpreter or "
533 "shared libraries may be denied.\n");
534 return 1;
535
536err_close_ruleset:
537 close(ruleset_fd);
538 return 1;
539}
540

source code of linux/samples/landlock/sandboxer.c