1 files changed, 311 insertions, 0 deletions
diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
new file mode 100644
index 0000000000..e2056c8b90
--- /dev/null
+++ b/samples/landlock/sandboxer.c
@@ -0,0 +1,311 @@
+// 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 | \
+	LANDLOCK_ACCESS_FS_TRUNCATE)
+
+/* 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 | \
+	LANDLOCK_ACCESS_FS_TRUNCATE)
+
+/* clang-format on */
+
+#define LANDLOCK_ABI_LAST 3
+
+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\n",
+			ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
+		fprintf(stderr,
+			"This sandboxer can use Landlock features "
+			"up to ABI version %d.\n",
+			LANDLOCK_ABI_LAST);
+		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. */
+	switch (abi) {
+	case 1:
+		/*
+		 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2
+		 *
+		 * Note: The "refer" operations (file renaming and linking
+		 * across different directories) are always forbidden when using
+		 * Landlock with ABI 1.
+		 *
+		 * If only ABI 1 is available, this sandboxer knowingly forbids
+		 * refer operations.
+		 *
+		 * If a program *needs* to do refer operations after enabling
+		 * Landlock, it can not use Landlock at ABI level 1.  To be
+		 * compatible with different kernel versions, such programs
+		 * should then fall back to not restrict themselves at all if
+		 * the running kernel only supports ABI 1.
+		 */
+		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
+		__attribute__((fallthrough));
+	case 2:
+		/* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
+		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
+
+		fprintf(stderr,
+			"Hint: You should update the running kernel "
+			"to leverage Landlock features "
+			"provided by ABI version %d (instead of %d).\n",
+			LANDLOCK_ABI_LAST, abi);
+		__attribute__((fallthrough));
+	case LANDLOCK_ABI_LAST:
+		break;
+	default:
+		fprintf(stderr,
+			"Hint: You should update this sandboxer "
+			"to leverage Landlock features "
+			"provided by ABI version %d (instead of %d).\n",
+			abi, LANDLOCK_ABI_LAST);
+	}
+	access_fs_ro &= ruleset_attr.handled_access_fs;
+	access_fs_rw &= ruleset_attr.handled_access_fs;
+
+	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;
+}