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
32 static inline int
landlock_create_ruleset(const struct landlock_ruleset_attr * const attr,const size_t size,const __u32 flags)33 landlock_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
landlock_add_rule(const int ruleset_fd,const enum landlock_rule_type rule_type,const void * const rule_attr,const __u32 flags)41 static 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
landlock_restrict_self(const int ruleset_fd,const __u32 flags)52 static 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
str2num(const char * numstr,__u64 * num_dst)67 static 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
parse_path(char * env_path,const char *** const path_list)86 static 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 LANDLOCK_ACCESS_FS_RESOLVE_UNIX)
116
117 /* clang-format on */
118
populate_ruleset_fs(const char * const env_var,const int ruleset_fd,const __u64 allowed_access)119 static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
120 const __u64 allowed_access)
121 {
122 int num_paths, i, ret = 1;
123 char *env_path_name;
124 const char **path_list = NULL;
125 struct landlock_path_beneath_attr path_beneath = {
126 .parent_fd = -1,
127 };
128
129 env_path_name = getenv(env_var);
130 if (!env_path_name) {
131 /* Prevents users to forget a setting. */
132 fprintf(stderr, "Missing environment variable %s\n", env_var);
133 return 1;
134 }
135 env_path_name = strdup(env_path_name);
136 unsetenv(env_var);
137 num_paths = parse_path(env_path_name, &path_list);
138 if (num_paths < 0) {
139 fprintf(stderr, "Failed to allocate memory\n");
140 goto out_free_name;
141 }
142 if (num_paths == 1 && path_list[0][0] == '\0') {
143 /*
144 * Allows to not use all possible restrictions (e.g. use
145 * LL_FS_RO without LL_FS_RW).
146 */
147 ret = 0;
148 goto out_free_name;
149 }
150
151 for (i = 0; i < num_paths; i++) {
152 struct stat statbuf;
153
154 path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC);
155 if (path_beneath.parent_fd < 0) {
156 fprintf(stderr, "Failed to open \"%s\": %s\n",
157 path_list[i], strerror(errno));
158 continue;
159 }
160 if (fstat(path_beneath.parent_fd, &statbuf)) {
161 fprintf(stderr, "Failed to stat \"%s\": %s\n",
162 path_list[i], strerror(errno));
163 close(path_beneath.parent_fd);
164 goto out_free_name;
165 }
166 path_beneath.allowed_access = allowed_access;
167 if (!S_ISDIR(statbuf.st_mode))
168 path_beneath.allowed_access &= ACCESS_FILE;
169 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
170 &path_beneath, 0)) {
171 fprintf(stderr,
172 "Failed to update the ruleset with \"%s\": %s\n",
173 path_list[i], strerror(errno));
174 close(path_beneath.parent_fd);
175 goto out_free_name;
176 }
177 close(path_beneath.parent_fd);
178 }
179 ret = 0;
180
181 out_free_name:
182 free(path_list);
183 free(env_path_name);
184 return ret;
185 }
186
populate_ruleset_net(const char * const env_var,const int ruleset_fd,const __u64 allowed_access)187 static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
188 const __u64 allowed_access)
189 {
190 int ret = 1;
191 char *env_port_name, *env_port_name_next, *strport;
192 struct landlock_net_port_attr net_port = {
193 .allowed_access = allowed_access,
194 };
195
196 env_port_name = getenv(env_var);
197 if (!env_port_name)
198 return 0;
199 env_port_name = strdup(env_port_name);
200 unsetenv(env_var);
201
202 env_port_name_next = env_port_name;
203 while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) {
204 __u64 port;
205
206 if (strcmp(strport, "") == 0)
207 continue;
208
209 if (str2num(strport, &port)) {
210 fprintf(stderr, "Failed to parse port at \"%s\"\n",
211 strport);
212 goto out_free_name;
213 }
214 net_port.port = port;
215 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT,
216 &net_port, 0)) {
217 fprintf(stderr,
218 "Failed to update the ruleset with port \"%llu\": %s\n",
219 net_port.port, strerror(errno));
220 goto out_free_name;
221 }
222 }
223 ret = 0;
224
225 out_free_name:
226 free(env_port_name);
227 return ret;
228 }
229
230 /* Returns true on error, false otherwise. */
check_ruleset_scope(const char * const env_var,struct landlock_ruleset_attr * ruleset_attr)231 static bool check_ruleset_scope(const char *const env_var,
232 struct landlock_ruleset_attr *ruleset_attr)
233 {
234 char *env_type_scope, *env_type_scope_next, *ipc_scoping_name;
235 bool error = false;
236 bool abstract_scoping = false;
237 bool signal_scoping = false;
238
239 /* Scoping is not supported by Landlock ABI */
240 if (!(ruleset_attr->scoped &
241 (LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | LANDLOCK_SCOPE_SIGNAL)))
242 goto out_unset;
243
244 env_type_scope = getenv(env_var);
245 /* Scoping is not supported by the user */
246 if (!env_type_scope || strcmp("", env_type_scope) == 0)
247 goto out_unset;
248
249 env_type_scope = strdup(env_type_scope);
250 env_type_scope_next = env_type_scope;
251 while ((ipc_scoping_name =
252 strsep(&env_type_scope_next, ENV_DELIMITER))) {
253 if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) {
254 abstract_scoping = true;
255 } else if (strcmp("s", ipc_scoping_name) == 0 &&
256 !signal_scoping) {
257 signal_scoping = true;
258 } else {
259 fprintf(stderr, "Unknown or duplicate scope \"%s\"\n",
260 ipc_scoping_name);
261 error = true;
262 goto out_free_name;
263 }
264 }
265
266 out_free_name:
267 free(env_type_scope);
268
269 out_unset:
270 if (!abstract_scoping)
271 ruleset_attr->scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET;
272 if (!signal_scoping)
273 ruleset_attr->scoped &= ~LANDLOCK_SCOPE_SIGNAL;
274
275 unsetenv(env_var);
276 return error;
277 }
278
279 /* clang-format off */
280
281 #define ACCESS_FS_ROUGHLY_READ ( \
282 LANDLOCK_ACCESS_FS_EXECUTE | \
283 LANDLOCK_ACCESS_FS_READ_FILE | \
284 LANDLOCK_ACCESS_FS_READ_DIR)
285
286 #define ACCESS_FS_ROUGHLY_WRITE ( \
287 LANDLOCK_ACCESS_FS_WRITE_FILE | \
288 LANDLOCK_ACCESS_FS_REMOVE_DIR | \
289 LANDLOCK_ACCESS_FS_REMOVE_FILE | \
290 LANDLOCK_ACCESS_FS_MAKE_CHAR | \
291 LANDLOCK_ACCESS_FS_MAKE_DIR | \
292 LANDLOCK_ACCESS_FS_MAKE_REG | \
293 LANDLOCK_ACCESS_FS_MAKE_SOCK | \
294 LANDLOCK_ACCESS_FS_MAKE_FIFO | \
295 LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
296 LANDLOCK_ACCESS_FS_MAKE_SYM | \
297 LANDLOCK_ACCESS_FS_REFER | \
298 LANDLOCK_ACCESS_FS_TRUNCATE | \
299 LANDLOCK_ACCESS_FS_IOCTL_DEV | \
300 LANDLOCK_ACCESS_FS_RESOLVE_UNIX)
301
302 /* clang-format on */
303
304 #define LANDLOCK_ABI_LAST 9
305
306 #define XSTR(s) #s
307 #define STR(s) XSTR(s)
308
309 /* clang-format off */
310
311 static const char help[] =
312 "usage: " ENV_FS_RO_NAME "=\"...\" " ENV_FS_RW_NAME "=\"...\" "
313 "[other environment variables] %1$s <cmd> [args]...\n"
314 "\n"
315 "Execute the given command in a restricted environment.\n"
316 "Multi-valued settings (lists of ports, paths, scopes) are colon-delimited.\n"
317 "\n"
318 "Mandatory settings:\n"
319 "* " ENV_FS_RO_NAME ": paths allowed to be used in a read-only way\n"
320 "* " ENV_FS_RW_NAME ": paths allowed to be used in a read-write way\n"
321 "\n"
322 "Optional settings (when not set, their associated access check "
323 "is always allowed, which is different from an empty string which "
324 "means an empty list):\n"
325 "* " ENV_TCP_BIND_NAME ": ports allowed to bind (server)\n"
326 "* " ENV_TCP_CONNECT_NAME ": ports allowed to connect (client)\n"
327 "* " ENV_SCOPED_NAME ": actions denied on the outside of the landlock domain\n"
328 " - \"a\" to restrict opening abstract unix sockets\n"
329 " - \"s\" to restrict sending signals\n"
330 "\n"
331 "A sandboxer should not log denied access requests to avoid spamming logs, "
332 "but to test audit we can set " ENV_FORCE_LOG_NAME "=1\n"
333 "\n"
334 "Example:\n"
335 ENV_FS_RO_NAME "=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
336 ENV_FS_RW_NAME "=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
337 ENV_TCP_BIND_NAME "=\"9418\" "
338 ENV_TCP_CONNECT_NAME "=\"80:443\" "
339 ENV_SCOPED_NAME "=\"a:s\" "
340 "%1$s bash -i\n"
341 "\n"
342 "This sandboxer can use Landlock features up to ABI version "
343 STR(LANDLOCK_ABI_LAST) ".\n";
344
345 /* clang-format on */
346
main(const int argc,char * const argv[],char * const * const envp)347 int main(const int argc, char *const argv[], char *const *const envp)
348 {
349 const char *cmd_path;
350 char *const *cmd_argv;
351 int ruleset_fd, abi;
352 char *env_port_name, *env_force_log;
353 __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
354 access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
355
356 struct landlock_ruleset_attr ruleset_attr = {
357 .handled_access_fs = access_fs_rw,
358 .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP |
359 LANDLOCK_ACCESS_NET_CONNECT_TCP,
360 .scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
361 LANDLOCK_SCOPE_SIGNAL,
362 };
363 int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
364 int set_restrict_flags = 0;
365
366 if (argc < 2) {
367 fprintf(stderr, help, argv[0]);
368 return 1;
369 }
370
371 abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
372 if (abi < 0) {
373 const int err = errno;
374
375 perror("Failed to check Landlock compatibility");
376 switch (err) {
377 case ENOSYS:
378 fprintf(stderr,
379 "Hint: Landlock is not supported by the current kernel. "
380 "To support it, build the kernel with "
381 "CONFIG_SECURITY_LANDLOCK=y and prepend "
382 "\"landlock,\" to the content of CONFIG_LSM.\n");
383 break;
384 case EOPNOTSUPP:
385 fprintf(stderr,
386 "Hint: Landlock is currently disabled. "
387 "It can be enabled in the kernel configuration by "
388 "prepending \"landlock,\" to the content of CONFIG_LSM, "
389 "or at boot time by setting the same content to the "
390 "\"lsm\" kernel parameter.\n");
391 break;
392 }
393 return 1;
394 }
395
396 /* Best-effort security. */
397 switch (abi) {
398 case 1:
399 /*
400 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2
401 *
402 * Note: The "refer" operations (file renaming and linking
403 * across different directories) are always forbidden when using
404 * Landlock with ABI 1.
405 *
406 * If only ABI 1 is available, this sandboxer knowingly forbids
407 * refer operations.
408 *
409 * If a program *needs* to do refer operations after enabling
410 * Landlock, it can not use Landlock at ABI level 1. To be
411 * compatible with different kernel versions, such programs
412 * should then fall back to not restrict themselves at all if
413 * the running kernel only supports ABI 1.
414 */
415 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
416 __attribute__((fallthrough));
417 case 2:
418 /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
419 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
420 __attribute__((fallthrough));
421 case 3:
422 /* Removes network support for ABI < 4 */
423 ruleset_attr.handled_access_net &=
424 ~(LANDLOCK_ACCESS_NET_BIND_TCP |
425 LANDLOCK_ACCESS_NET_CONNECT_TCP);
426 __attribute__((fallthrough));
427 case 4:
428 /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */
429 ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV;
430
431 __attribute__((fallthrough));
432 case 5:
433 /* Removes LANDLOCK_SCOPE_* for ABI < 6 */
434 ruleset_attr.scoped &= ~(LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
435 LANDLOCK_SCOPE_SIGNAL);
436 __attribute__((fallthrough));
437 case 6:
438 /* Removes LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON for ABI < 7 */
439 supported_restrict_flags &=
440 ~LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
441 __attribute__((fallthrough));
442 case 7:
443 case 8:
444 /* Removes LANDLOCK_ACCESS_FS_RESOLVE_UNIX for ABI < 9 */
445 ruleset_attr.handled_access_fs &=
446 ~LANDLOCK_ACCESS_FS_RESOLVE_UNIX;
447 /* Must be printed for any ABI < LANDLOCK_ABI_LAST. */
448 fprintf(stderr,
449 "Hint: You should update the running kernel "
450 "to leverage Landlock features "
451 "provided by ABI version %d (instead of %d).\n",
452 LANDLOCK_ABI_LAST, abi);
453 __attribute__((fallthrough));
454 case LANDLOCK_ABI_LAST:
455 break;
456 default:
457 fprintf(stderr,
458 "Hint: You should update this sandboxer "
459 "to leverage Landlock features "
460 "provided by ABI version %d (instead of %d).\n",
461 abi, LANDLOCK_ABI_LAST);
462 }
463 access_fs_ro &= ruleset_attr.handled_access_fs;
464 access_fs_rw &= ruleset_attr.handled_access_fs;
465
466 /* Removes bind access attribute if not supported by a user. */
467 env_port_name = getenv(ENV_TCP_BIND_NAME);
468 if (!env_port_name) {
469 ruleset_attr.handled_access_net &=
470 ~LANDLOCK_ACCESS_NET_BIND_TCP;
471 }
472 /* Removes connect access attribute if not supported by a user. */
473 env_port_name = getenv(ENV_TCP_CONNECT_NAME);
474 if (!env_port_name) {
475 ruleset_attr.handled_access_net &=
476 ~LANDLOCK_ACCESS_NET_CONNECT_TCP;
477 }
478
479 if (check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr))
480 return 1;
481
482 /* Enables optional logs. */
483 env_force_log = getenv(ENV_FORCE_LOG_NAME);
484 if (env_force_log) {
485 if (strcmp(env_force_log, "1") != 0) {
486 fprintf(stderr, "Unknown value for " ENV_FORCE_LOG_NAME
487 " (only \"1\" is handled)\n");
488 return 1;
489 }
490 if (!(supported_restrict_flags &
491 LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON)) {
492 fprintf(stderr,
493 "Audit logs not supported by current kernel\n");
494 return 1;
495 }
496 set_restrict_flags |= LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
497 unsetenv(ENV_FORCE_LOG_NAME);
498 }
499
500 ruleset_fd =
501 landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
502 if (ruleset_fd < 0) {
503 perror("Failed to create a ruleset");
504 return 1;
505 }
506
507 if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
508 goto err_close_ruleset;
509 }
510 if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
511 goto err_close_ruleset;
512 }
513
514 if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
515 LANDLOCK_ACCESS_NET_BIND_TCP)) {
516 goto err_close_ruleset;
517 }
518 if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd,
519 LANDLOCK_ACCESS_NET_CONNECT_TCP)) {
520 goto err_close_ruleset;
521 }
522
523 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
524 perror("Failed to restrict privileges");
525 goto err_close_ruleset;
526 }
527 if (landlock_restrict_self(ruleset_fd, set_restrict_flags)) {
528 perror("Failed to enforce ruleset");
529 goto err_close_ruleset;
530 }
531 close(ruleset_fd);
532
533 cmd_path = argv[1];
534 cmd_argv = argv + 1;
535 fprintf(stderr, "Executing the sandboxed command...\n");
536 execvpe(cmd_path, cmd_argv, envp);
537 fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
538 strerror(errno));
539 fprintf(stderr, "Hint: access to the binary, the interpreter or "
540 "shared libraries may be denied.\n");
541 return 1;
542
543 err_close_ruleset:
544 close(ruleset_fd);
545 return 1;
546 }
547