[linux-block.git] / samples / landlock / sandboxer.c

// SPDX-License-Identifier: BSD-3-Clause
/*
 * Simple Landlock sandbox manager able to launch a process restricted by a
 * user-defined filesystem access control policy.
 *
 * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
 * Copyright © 2020 ANSSI
 */

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/landlock.h>
#include <linux/prctl.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <unistd.h>

#ifndef landlock_create_ruleset
static inline int
landlock_create_ruleset(const struct landlock_ruleset_attr *const attr,
			const size_t size, const __u32 flags)
{
	return syscall(__NR_landlock_create_ruleset, attr, size, flags);
}
#endif

#ifndef landlock_add_rule
static inline int landlock_add_rule(const int ruleset_fd,
				    const enum landlock_rule_type rule_type,
				    const void *const rule_attr,
				    const __u32 flags)
{
	return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr,
		       flags);
}
#endif

#ifndef landlock_restrict_self
static inline int landlock_restrict_self(const int ruleset_fd,
					 const __u32 flags)
{
	return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
}
#endif

#define ENV_FS_RO_NAME "LL_FS_RO"
#define ENV_FS_RW_NAME "LL_FS_RW"
#define ENV_PATH_TOKEN ":"

static int parse_path(char *env_path, const char ***const path_list)
{
	int i, num_paths = 0;

	if (env_path) {
		num_paths++;
		for (i = 0; env_path[i]; i++) {
			if (env_path[i] == ENV_PATH_TOKEN[0])
				num_paths++;
		}
	}
	*path_list = malloc(num_paths * sizeof(**path_list));
	for (i = 0; i < num_paths; i++)
		(*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN);

	return num_paths;
}

/* clang-format off */

#define ACCESS_FILE ( \
	LANDLOCK_ACCESS_FS_EXECUTE | \
	LANDLOCK_ACCESS_FS_WRITE_FILE | \
	LANDLOCK_ACCESS_FS_READ_FILE)

/* clang-format on */

static int populate_ruleset(const char *const env_var, const int ruleset_fd,
			    const __u64 allowed_access)
{
	int num_paths, i, ret = 1;
	char *env_path_name;
	const char **path_list = NULL;
	struct landlock_path_beneath_attr path_beneath = {
		.parent_fd = -1,
	};

	env_path_name = getenv(env_var);
	if (!env_path_name) {
		/* Prevents users to forget a setting. */
		fprintf(stderr, "Missing environment variable %s\n", env_var);
		return 1;
	}
	env_path_name = strdup(env_path_name);
	unsetenv(env_var);
	num_paths = parse_path(env_path_name, &path_list);
	if (num_paths == 1 && path_list[0][0] == '\0') {
		/*
		 * Allows to not use all possible restrictions (e.g. use
		 * LL_FS_RO without LL_FS_RW).
		 */
		ret = 0;
		goto out_free_name;
	}

	for (i = 0; i < num_paths; i++) {
		struct stat statbuf;

		path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC);
		if (path_beneath.parent_fd < 0) {
			fprintf(stderr, "Failed to open \"%s\": %s\n",
				path_list[i], strerror(errno));
			goto out_free_name;
		}
		if (fstat(path_beneath.parent_fd, &statbuf)) {
			close(path_beneath.parent_fd);
			goto out_free_name;
		}
		path_beneath.allowed_access = allowed_access;
		if (!S_ISDIR(statbuf.st_mode))
			path_beneath.allowed_access &= ACCESS_FILE;
		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
				      &path_beneath, 0)) {
			fprintf(stderr,
				"Failed to update the ruleset with \"%s\": %s\n",
				path_list[i], strerror(errno));
			close(path_beneath.parent_fd);
			goto out_free_name;
		}
		close(path_beneath.parent_fd);
	}
	ret = 0;

out_free_name:
	free(path_list);
	free(env_path_name);
	return ret;
}

/* clang-format off */

#define ACCESS_FS_ROUGHLY_READ ( \
	LANDLOCK_ACCESS_FS_EXECUTE | \
	LANDLOCK_ACCESS_FS_READ_FILE | \
	LANDLOCK_ACCESS_FS_READ_DIR)

#define ACCESS_FS_ROUGHLY_WRITE ( \
	LANDLOCK_ACCESS_FS_WRITE_FILE | \
	LANDLOCK_ACCESS_FS_REMOVE_DIR | \
	LANDLOCK_ACCESS_FS_REMOVE_FILE | \
	LANDLOCK_ACCESS_FS_MAKE_CHAR | \
	LANDLOCK_ACCESS_FS_MAKE_DIR | \
	LANDLOCK_ACCESS_FS_MAKE_REG | \
	LANDLOCK_ACCESS_FS_MAKE_SOCK | \
	LANDLOCK_ACCESS_FS_MAKE_FIFO | \
	LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
	LANDLOCK_ACCESS_FS_MAKE_SYM | \
	LANDLOCK_ACCESS_FS_REFER)

#define ACCESS_ABI_2 ( \
	LANDLOCK_ACCESS_FS_REFER)

/* clang-format on */

int main(const int argc, char *const argv[], char *const *const envp)
{
	const char *cmd_path;
	char *const *cmd_argv;
	int ruleset_fd, abi;
	__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
	struct landlock_ruleset_attr ruleset_attr = {
		.handled_access_fs = access_fs_rw,
	};

	if (argc < 2) {
		fprintf(stderr,
			"usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
			ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
		fprintf(stderr,
			"Launch a command in a restricted environment.\n\n");
		fprintf(stderr, "Environment variables containing paths, "
				"each separated by a colon:\n");
		fprintf(stderr,
			"* %s: list of paths allowed to be used in a read-only way.\n",
			ENV_FS_RO_NAME);
		fprintf(stderr,
			"* %s: list of paths allowed to be used in a read-write way.\n",
			ENV_FS_RW_NAME);
		fprintf(stderr,
			"\nexample:\n"
			"%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
			"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
			"%s bash -i\n",
			ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
		return 1;
	}

	abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
	if (abi < 0) {
		const int err = errno;

		perror("Failed to check Landlock compatibility");
		switch (err) {
		case ENOSYS:
			fprintf(stderr,
				"Hint: Landlock is not supported by the current kernel. "
				"To support it, build the kernel with "
				"CONFIG_SECURITY_LANDLOCK=y and prepend "
				"\"landlock,\" to the content of CONFIG_LSM.\n");
			break;
		case EOPNOTSUPP:
			fprintf(stderr,
				"Hint: Landlock is currently disabled. "
				"It can be enabled in the kernel configuration by "
				"prepending \"landlock,\" to the content of CONFIG_LSM, "
				"or at boot time by setting the same content to the "
				"\"lsm\" kernel parameter.\n");
			break;
		}
		return 1;
	}
	/* Best-effort security. */
	if (abi < 2) {
		ruleset_attr.handled_access_fs &= ~ACCESS_ABI_2;
		access_fs_ro &= ~ACCESS_ABI_2;
		access_fs_rw &= ~ACCESS_ABI_2;
	}

	ruleset_fd =
		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
	if (ruleset_fd < 0) {
		perror("Failed to create a ruleset");
		return 1;
	}
	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
		goto err_close_ruleset;
	}
	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
		goto err_close_ruleset;
	}
	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
		perror("Failed to restrict privileges");
		goto err_close_ruleset;
	}
	if (landlock_restrict_self(ruleset_fd, 0)) {
		perror("Failed to enforce ruleset");
		goto err_close_ruleset;
	}
	close(ruleset_fd);

	cmd_path = argv[1];
	cmd_argv = argv + 1;
	execvpe(cmd_path, cmd_argv, envp);
	fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
		strerror(errno));
	fprintf(stderr, "Hint: access to the binary, the interpreter or "
			"shared libraries may be denied.\n");
	return 1;

err_close_ruleset:
	close(ruleset_fd);
	return 1;
}
Commit	Line	Data
ba84b0bf MS	1	// SPDX-License-Identifier: BSD-3-Clause
	2	/*
	3	* Simple Landlock sandbox manager able to launch a process restricted by a
	4	* user-defined filesystem access control policy.
	5	*
	6	* Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
	7	* Copyright © 2020 ANSSI
	8	*/
	9
	10	#define _GNU_SOURCE
	11	#include <errno.h>
	12	#include <fcntl.h>
	13	#include <linux/landlock.h>
	14	#include <linux/prctl.h>
	15	#include <stddef.h>
	16	#include <stdio.h>
	17	#include <stdlib.h>
	18	#include <string.h>
	19	#include <sys/prctl.h>
	20	#include <sys/stat.h>
	21	#include <sys/syscall.h>
	22	#include <unistd.h>
	23
	24	#ifndef landlock_create_ruleset
81709f3d MS	25	static inline int
	26	landlock_create_ruleset(const struct landlock_ruleset_attr *const attr,
	27	const size_t size, const __u32 flags)
ba84b0bf MS	28	{
	29	return syscall(__NR_landlock_create_ruleset, attr, size, flags);
	30	}
	31	#endif
	32
	33	#ifndef landlock_add_rule
	34	static inline int landlock_add_rule(const int ruleset_fd,
81709f3d MS	35	const enum landlock_rule_type rule_type,
	36	const void *const rule_attr,
	37	const __u32 flags)
ba84b0bf	38	{
81709f3d MS	39	return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr,
81709f3d MS	40	flags);
ba84b0bf MS	41	}
	42	#endif
	43
	44	#ifndef landlock_restrict_self
	45	static inline int landlock_restrict_self(const int ruleset_fd,
81709f3d	46	const __u32 flags)
ba84b0bf MS	47	{
	48	return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
	49	}
	50	#endif
	51
	52	#define ENV_FS_RO_NAME "LL_FS_RO"
	53	#define ENV_FS_RW_NAME "LL_FS_RW"
	54	#define ENV_PATH_TOKEN ":"
	55
	56	static int parse_path(char env_path, const char **const path_list)
	57	{
	58	int i, num_paths = 0;
	59
	60	if (env_path) {
	61	num_paths++;
	62	for (i = 0; env_path[i]; i++) {
	63	if (env_path[i] == ENV_PATH_TOKEN[0])
	64	num_paths++;
	65	}
	66	}
	67	path_list = malloc(num_paths sizeof(**path_list));
	68	for (i = 0; i < num_paths; i++)
	69	(*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN);
	70
	71	return num_paths;
	72	}
	73
9805a722 MS	74	/* clang-format off */
9805a722 MS	75
ba84b0bf MS	76	#define ACCESS_FILE ( \
	77	LANDLOCK_ACCESS_FS_EXECUTE \| \
	78	LANDLOCK_ACCESS_FS_WRITE_FILE \| \
	79	LANDLOCK_ACCESS_FS_READ_FILE)
	80
9805a722 MS	81	/* clang-format on */
9805a722 MS	82
81709f3d MS	83	static int populate_ruleset(const char *const env_var, const int ruleset_fd,
81709f3d MS	84	const __u64 allowed_access)
ba84b0bf MS	85	{
	86	int num_paths, i, ret = 1;
	87	char *env_path_name;
	88	const char **path_list = NULL;
	89	struct landlock_path_beneath_attr path_beneath = {
	90	.parent_fd = -1,
	91	};
	92
	93	env_path_name = getenv(env_var);
	94	if (!env_path_name) {
	95	/* Prevents users to forget a setting. */
	96	fprintf(stderr, "Missing environment variable %s\n", env_var);
	97	return 1;
	98	}
	99	env_path_name = strdup(env_path_name);
	100	unsetenv(env_var);
	101	num_paths = parse_path(env_path_name, &path_list);
	102	if (num_paths == 1 && path_list[0][0] == '\0') {
	103	/*
	104	* Allows to not use all possible restrictions (e.g. use
	105	* LL_FS_RO without LL_FS_RW).
	106	*/
	107	ret = 0;
	108	goto out_free_name;
	109	}
	110
	111	for (i = 0; i < num_paths; i++) {
	112	struct stat statbuf;
	113
81709f3d	114	path_beneath.parent_fd = open(path_list[i], O_PATH \| O_CLOEXEC);
ba84b0bf MS	115	if (path_beneath.parent_fd < 0) {
ba84b0bf MS	116	fprintf(stderr, "Failed to open \"%s\": %s\n",
81709f3d	117	path_list[i], strerror(errno));
ba84b0bf MS	118	goto out_free_name;
	119	}
	120	if (fstat(path_beneath.parent_fd, &statbuf)) {
	121	close(path_beneath.parent_fd);
	122	goto out_free_name;
	123	}
	124	path_beneath.allowed_access = allowed_access;
	125	if (!S_ISDIR(statbuf.st_mode))
	126	path_beneath.allowed_access &= ACCESS_FILE;
	127	if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
81709f3d MS	128	&path_beneath, 0)) {
	129	fprintf(stderr,
	130	"Failed to update the ruleset with \"%s\": %s\n",
	131	path_list[i], strerror(errno));
ba84b0bf MS	132	close(path_beneath.parent_fd);
	133	goto out_free_name;
	134	}
	135	close(path_beneath.parent_fd);
	136	}
	137	ret = 0;
	138
	139	out_free_name:
66b513b7	140	free(path_list);
ba84b0bf MS	141	free(env_path_name);
	142	return ret;
	143	}
	144
9805a722 MS	145	/* clang-format off */
9805a722 MS	146
ba84b0bf MS	147	#define ACCESS_FS_ROUGHLY_READ ( \
	148	LANDLOCK_ACCESS_FS_EXECUTE \| \
	149	LANDLOCK_ACCESS_FS_READ_FILE \| \
	150	LANDLOCK_ACCESS_FS_READ_DIR)
	151
	152	#define ACCESS_FS_ROUGHLY_WRITE ( \
	153	LANDLOCK_ACCESS_FS_WRITE_FILE \| \
	154	LANDLOCK_ACCESS_FS_REMOVE_DIR \| \
	155	LANDLOCK_ACCESS_FS_REMOVE_FILE \| \
	156	LANDLOCK_ACCESS_FS_MAKE_CHAR \| \
	157	LANDLOCK_ACCESS_FS_MAKE_DIR \| \
	158	LANDLOCK_ACCESS_FS_MAKE_REG \| \
	159	LANDLOCK_ACCESS_FS_MAKE_SOCK \| \
	160	LANDLOCK_ACCESS_FS_MAKE_FIFO \| \
	161	LANDLOCK_ACCESS_FS_MAKE_BLOCK \| \
76b902f8 MS	162	LANDLOCK_ACCESS_FS_MAKE_SYM \| \
	163	LANDLOCK_ACCESS_FS_REFER)
	164
	165	#define ACCESS_ABI_2 ( \
	166	LANDLOCK_ACCESS_FS_REFER)
ba84b0bf	167
9805a722 MS	168	/* clang-format on */
9805a722 MS	169
ba84b0bf MS	170	int main(const int argc, char const argv[], char const *const envp)
	171	{
	172	const char *cmd_path;
	173	char const cmd_argv;
76b902f8 MS	174	int ruleset_fd, abi;
	175	__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
	176	access_fs_rw = ACCESS_FS_ROUGHLY_READ \| ACCESS_FS_ROUGHLY_WRITE;
ba84b0bf	177	struct landlock_ruleset_attr ruleset_attr = {
76b902f8	178	.handled_access_fs = access_fs_rw,
ba84b0bf MS	179	};
	180
	181	if (argc < 2) {
81709f3d MS	182	fprintf(stderr,
	183	"usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
	184	ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
	185	fprintf(stderr,
	186	"Launch a command in a restricted environment.\n\n");
ba84b0bf MS	187	fprintf(stderr, "Environment variables containing paths, "
ba84b0bf MS	188	"each separated by a colon:\n");
81709f3d MS	189	fprintf(stderr,
	190	"* %s: list of paths allowed to be used in a read-only way.\n",
	191	ENV_FS_RO_NAME);
	192	fprintf(stderr,
	193	"* %s: list of paths allowed to be used in a read-write way.\n",
	194	ENV_FS_RW_NAME);
	195	fprintf(stderr,
	196	"\nexample:\n"
	197	"%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
	198	"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
	199	"%s bash -i\n",
	200	ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
ba84b0bf MS	201	return 1;
	202	}
	203
76b902f8 MS	204	abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
76b902f8 MS	205	if (abi < 0) {
ba84b0bf MS	206	const int err = errno;
ba84b0bf MS	207
76b902f8	208	perror("Failed to check Landlock compatibility");
ba84b0bf MS	209	switch (err) {
ba84b0bf MS	210	case ENOSYS:
81709f3d MS	211	fprintf(stderr,
	212	"Hint: Landlock is not supported by the current kernel. "
	213	"To support it, build the kernel with "
	214	"CONFIG_SECURITY_LANDLOCK=y and prepend "
	215	"\"landlock,\" to the content of CONFIG_LSM.\n");
ba84b0bf MS	216	break;
ba84b0bf MS	217	case EOPNOTSUPP:
81709f3d MS	218	fprintf(stderr,
	219	"Hint: Landlock is currently disabled. "
	220	"It can be enabled in the kernel configuration by "
	221	"prepending \"landlock,\" to the content of CONFIG_LSM, "
	222	"or at boot time by setting the same content to the "
	223	"\"lsm\" kernel parameter.\n");
ba84b0bf MS	224	break;
	225	}
	226	return 1;
	227	}
76b902f8 MS	228	/* Best-effort security. */
	229	if (abi < 2) {
	230	ruleset_attr.handled_access_fs &= ~ACCESS_ABI_2;
	231	access_fs_ro &= ~ACCESS_ABI_2;
	232	access_fs_rw &= ~ACCESS_ABI_2;
	233	}
	234
	235	ruleset_fd =
	236	landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
	237	if (ruleset_fd < 0) {
	238	perror("Failed to create a ruleset");
	239	return 1;
	240	}
	241	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
ba84b0bf MS	242	goto err_close_ruleset;
ba84b0bf MS	243	}
76b902f8	244	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
ba84b0bf MS	245	goto err_close_ruleset;
	246	}
	247	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
	248	perror("Failed to restrict privileges");
	249	goto err_close_ruleset;
	250	}
	251	if (landlock_restrict_self(ruleset_fd, 0)) {
	252	perror("Failed to enforce ruleset");
	253	goto err_close_ruleset;
	254	}
	255	close(ruleset_fd);
	256
	257	cmd_path = argv[1];
	258	cmd_argv = argv + 1;
	259	execvpe(cmd_path, cmd_argv, envp);
	260	fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
81709f3d	261	strerror(errno));
ba84b0bf MS	262	fprintf(stderr, "Hint: access to the binary, the interpreter or "
	263	"shared libraries may be denied.\n");
	264	return 1;
	265
	266	err_close_ruleset:
	267	close(ruleset_fd);
	268	return 1;
	269	}