Merge tag 'landlock_v34' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

Pull Landlock LSM from James Morris:
 "Add Landlock, a new LSM from Mickaël Salaün.

  Briefly, Landlock provides for unprivileged application sandboxing.

  From Mickaël's cover letter:
    "The goal of Landlock is to enable to restrict ambient rights (e.g.
     global filesystem access) for a set of processes. Because Landlock
     is a stackable LSM [1], it makes possible to create safe security
     sandboxes as new security layers in addition to the existing
     system-wide access-controls. This kind of sandbox is expected to
     help mitigate the security impact of bugs or unexpected/malicious
     behaviors in user-space applications. Landlock empowers any
     process, including unprivileged ones, to securely restrict
     themselves.

     Landlock is inspired by seccomp-bpf but instead of filtering
     syscalls and their raw arguments, a Landlock rule can restrict the
     use of kernel objects like file hierarchies, according to the
     kernel semantic. Landlock also takes inspiration from other OS
     sandbox mechanisms: XNU Sandbox, FreeBSD Capsicum or OpenBSD
     Pledge/Unveil.

     In this current form, Landlock misses some access-control features.
     This enables to minimize this patch series and ease review. This
     series still addresses multiple use cases, especially with the
     combined use of seccomp-bpf: applications with built-in sandboxing,
     init systems, security sandbox tools and security-oriented APIs [2]"

  The cover letter and v34 posting is here:

      https://lore.kernel.org/linux-security-module/20210422154123.13086-1-mic@digikod.net/

  See also:

      https://landlock.io/

  This code has had extensive design discussion and review over several
  years"

Link: https://lore.kernel.org/lkml/50db058a-7dde-441b-a7f9-f6837fe8b69f@schaufler-ca.com/ [1]
Link: https://lore.kernel.org/lkml/f646e1c7-33cf-333f-070c-0a40ad0468cd@digikod.net/ [2]

* tag 'landlock_v34' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
  landlock: Enable user space to infer supported features
  landlock: Add user and kernel documentation
  samples/landlock: Add a sandbox manager example
  selftests/landlock: Add user space tests
  landlock: Add syscall implementations
  arch: Wire up Landlock syscalls
  fs,security: Add sb_delete hook
  landlock: Support filesystem access-control
  LSM: Infrastructure management of the superblock
  landlock: Add ptrace restrictions
  landlock: Set up the security framework and manage credentials
  landlock: Add ruleset and domain management
  landlock: Add object management

samples/Kconfig

@@ -124,6 +124,13 @@ config SAMPLE_HIDRAW
 	bool "hidraw sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL
 
+config SAMPLE_LANDLOCK
+	bool "Landlock example"
+	depends on CC_CAN_LINK && HEADERS_INSTALL
+	help
+	  Build a simple Landlock sandbox manager able to start a process
+	  restricted by a user-defined filesystem access control policy.
+
 config SAMPLE_PIDFD
 	bool "pidfd sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL

samples/Makefile

@@ -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/

samples/landlock/.gitignore

@@ -0,0 +1 @@
+/sandboxer

samples/landlock/Makefile

@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: BSD-3-Clause
+
+userprogs-always-y := sandboxer
+
+userccflags += -I usr/include
+
+.PHONY: all clean
+
+all:
+	$(MAKE) -C ../.. samples/landlock/
+
+clean:
+	$(MAKE) -C ../.. M=samples/landlock/ clean

samples/landlock/sandboxer.c

@@ -0,0 +1,238 @@
+// 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;
+}
+
+#define ACCESS_FILE ( \
+	LANDLOCK_ACCESS_FS_EXECUTE | \
+	LANDLOCK_ACCESS_FS_WRITE_FILE | \
+	LANDLOCK_ACCESS_FS_READ_FILE)
+
+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(env_path_name);
+	return ret;
+}
+
+#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)
+
+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_ruleset_attr ruleset_attr = {
+		.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_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;
+	}
+
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	if (ruleset_fd < 0) {
+		const int err = errno;
+
+		perror("Failed to create a ruleset");
+		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;
+	}
+	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd,
+				ACCESS_FS_ROUGHLY_READ)) {
+		goto err_close_ruleset;
+	}
+	if (populate_ruleset(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_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;
+}