@@ -124,6 +124,13 @@ config SAMPLE_HIDRAW
bool "hidraw sample"
depends on CC_CAN_LINK && HEADERS_INSTALL
+config SAMPLE_LANDLOCK
+ bool "Build Landlock sample code"
+ depends on HEADERS_INSTALL
+ help
+ Build a simple Landlock sandbox manager able to launch a process
+ restricted by a user-defined filesystem access-control security policy.
+
config SAMPLE_PIDFD
bool "pidfd sample"
depends on CC_CAN_LINK && HEADERS_INSTALL
@@ -11,6 +11,7 @@ obj-$(CONFIG_SAMPLE_KDB) += kdb/
obj-$(CONFIG_SAMPLE_KFIFO) += kfifo/
obj-$(CONFIG_SAMPLE_KOBJECT) += kobject/
obj-$(CONFIG_SAMPLE_KPROBES) += kprobes/
+subdir-$(CONFIG_SAMPLE_LANDLOCK) += landlock
obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch/
subdir-$(CONFIG_SAMPLE_PIDFD) += pidfd
obj-$(CONFIG_SAMPLE_QMI_CLIENT) += qmi/
new file mode 100644
@@ -0,0 +1 @@
+/sandboxer
new file mode 100644
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: BSD-3-Clause
+
+hostprogs := sandboxer
+
+always-y := $(hostprogs)
+
+KBUILD_HOSTCFLAGS += -I$(objtree)/usr/include
+
+.PHONY: all clean
+
+all:
+ $(MAKE) -C ../.. samples/landlock/
+
+clean:
+ $(MAKE) -C ../.. M=samples/landlock/ clean
new file mode 100644
@@ -0,0 +1,248 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Simple Landlock sandbox manager able to launch a process restricted by a
+ * user-defined filesystem access-control security 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_get_features
+static inline int landlock_get_features(
+ struct landlock_attr_features *const features_ptr,
+ const size_t features_size)
+{
+ errno = 0;
+ return syscall(__NR_landlock_get_features, features_ptr, features_size, 0);
+}
+#endif
+
+#ifndef landlock_create_ruleset
+static inline int landlock_create_ruleset(
+ const struct landlock_attr_ruleset *const ruleset_ptr,
+ const size_t ruleset_size)
+{
+ errno = 0;
+ return syscall(__NR_landlock_create_ruleset, ruleset_ptr, ruleset_size, 0);
+}
+#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_ptr, const size_t rule_size)
+{
+ errno = 0;
+ return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_ptr,
+ rule_size, 0);
+}
+#endif
+
+#ifndef landlock_enforce_ruleset
+static inline int landlock_enforce_ruleset(const int ruleset_fd)
+{
+ errno = 0;
+ return syscall(__NR_landlock_enforce_ruleset, ruleset_fd,
+ LANDLOCK_TARGET_CURRENT_THREAD, -1, 0);
+}
+#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, path_nb = 0;
+
+ if (env_path) {
+ path_nb++;
+ for (i = 0; env_path[i]; i++) {
+ if (env_path[i] == ENV_PATH_TOKEN[0])
+ path_nb++;
+ }
+ }
+ *path_list = malloc(path_nb * sizeof(**path_list));
+ for (i = 0; i < path_nb; i++)
+ (*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN);
+
+ return path_nb;
+}
+
+#define ACCESS_FILE ( \
+ LANDLOCK_ACCESS_FS_EXECUTE | \
+ LANDLOCK_ACCESS_FS_WRITE_FILE | \
+ LANDLOCK_ACCESS_FS_READ_FILE)
+
+static int populate_ruleset(
+ const struct landlock_attr_features *const attr_features,
+ const char *const env_var, const int ruleset_fd,
+ const __u64 allowed_access)
+{
+ int path_nb, i;
+ char *env_path_name;
+ const char **path_list = NULL;
+ struct landlock_attr_path_beneath path_beneath = {
+ .parent_fd = -1,
+ };
+
+ env_path_name = getenv(env_var);
+ if (!env_path_name) {
+ fprintf(stderr, "Missing environment variable %s\n", env_var);
+ return 1;
+ }
+ env_path_name = strdup(env_path_name);
+ unsetenv(env_var);
+ path_nb = parse_path(env_path_name, &path_list);
+ if (path_nb == 1 && path_list[0][0] == '\0') {
+ fprintf(stderr, "Missing path in %s\n", env_var);
+ goto err_free_name;
+ }
+
+ for (i = 0; i < path_nb; 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 err_free_name;
+ }
+ if (fstat(path_beneath.parent_fd, &statbuf)) {
+ close(path_beneath.parent_fd);
+ goto err_free_name;
+ }
+ /* Follows a best-effort approach. */
+ path_beneath.allowed_access = allowed_access &
+ attr_features->access_fs;
+ if (!S_ISDIR(statbuf.st_mode))
+ path_beneath.allowed_access &= ACCESS_FILE;
+ if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+ &path_beneath, sizeof(path_beneath))) {
+ fprintf(stderr, "Failed to update the ruleset with \"%s\": %s\n",
+ path_list[i], strerror(errno));
+ close(path_beneath.parent_fd);
+ goto err_free_name;
+ }
+ close(path_beneath.parent_fd);
+ }
+ free(env_path_name);
+ return 0;
+
+err_free_name:
+ free(env_path_name);
+ return 1;
+}
+
+#define ACCESS_FS_ROUGHLY_READ ( \
+ LANDLOCK_ACCESS_FS_EXECUTE | \
+ LANDLOCK_ACCESS_FS_READ_FILE | \
+ LANDLOCK_ACCESS_FS_READ_DIR | \
+ LANDLOCK_ACCESS_FS_CHROOT)
+
+#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)
+
+int main(const int argc, char *const argv[], char *const *const envp)
+{
+ const char *cmd_path;
+ char *const *cmd_argv;
+ int ruleset_fd;
+ struct landlock_attr_features attr_features;
+ struct landlock_attr_ruleset ruleset = {
+ .handled_access_fs = ACCESS_FS_ROUGHLY_READ |
+ ACCESS_FS_ROUGHLY_WRITE,
+ };
+
+ 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_RO_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;
+ }
+
+ if (landlock_get_features(&attr_features, sizeof(attr_features))) {
+ perror("Failed to probe the Landlock supported features");
+ switch (errno) {
+ case ENOSYS:
+ fprintf(stderr, "Hint: this kernel does not support Landlock.\n");
+ break;
+ case ENOPKG:
+ fprintf(stderr, "Hint: Landlock is currently disabled. It can be enabled in the kernel configuration or at boot with the \"lsm=landlock\" parameter.\n");
+ break;
+ }
+ return 1;
+ }
+ /* Follows a best-effort approach. */
+ ruleset.handled_access_fs &= attr_features.access_fs;
+ ruleset_fd = landlock_create_ruleset(&ruleset, sizeof(ruleset));
+ if (ruleset_fd < 0) {
+ perror("Failed to create a ruleset");
+ return 1;
+ }
+ if (populate_ruleset(&attr_features, ENV_FS_RO_NAME, ruleset_fd,
+ ACCESS_FS_ROUGHLY_READ)) {
+ goto err_close_ruleset;
+ }
+ if (populate_ruleset(&attr_features, ENV_FS_RW_NAME, ruleset_fd,
+ ACCESS_FS_ROUGHLY_READ |
+ ACCESS_FS_ROUGHLY_WRITE)) {
+ 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_enforce_ruleset(ruleset_fd)) {
+ 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;
+}
Add a basic sandbox tool to launch a command which can only access a whitelist of file hierarchies in a read-only or read-write way. Signed-off-by: Mickaël Salaün <mic@digikod.net> Cc: James Morris <jmorris@namei.org> Cc: Jann Horn <jannh@google.com> Cc: Kees Cook <keescook@chromium.org> Cc: Serge E. Hallyn <serge@hallyn.com> --- Changes since v19: * Update with the new Landlock syscalls. * Comply with commit 5f2fb52fac15 ("kbuild: rename hostprogs-y/always to hostprogs/always-y"). Changes since v16: * Switch syscall attribute pointer and size arguments. Changes since v15: * Update access right names. * Properly assign access right to files according to the new related syscall restriction. * Replace "select" with "depends on" HEADERS_INSTALL (suggested by Randy Dunlap). Changes since v14: * Fix Kconfig dependency. * Remove access rights that may be required for FD-only requests: mmap, truncate, getattr, lock, chmod, chown, chgrp, ioctl. * Fix useless hardcoded syscall number. * Use execvpe(). * Follow symlinks. * Extend help with common file paths. * Constify variables. * Clean up comments. * Improve error message. Changes since v11: * Add back the filesystem sandbox manager and update it to work with the new Landlock syscall. Previous changes: https://lore.kernel.org/lkml/20190721213116.23476-9-mic@digikod.net/ --- samples/Kconfig | 7 + samples/Makefile | 1 + samples/landlock/.gitignore | 1 + samples/landlock/Makefile | 15 +++ samples/landlock/sandboxer.c | 248 +++++++++++++++++++++++++++++++++++ 5 files changed, 272 insertions(+) create mode 100644 samples/landlock/.gitignore create mode 100644 samples/landlock/Makefile create mode 100644 samples/landlock/sandboxer.c