security: Add a static lockdown policy LSM
While existing LSMs can be extended to handle lockdown policy, distributions generally want to be able to apply a straightforward static policy. This patch adds a simple LSM that can be configured to reject either integrity or all lockdown queries, and can be configured at runtime (through securityfs), boot time (via a kernel parameter) or build time (via a kconfig option). Based on initial code by David Howells. Signed-off-by: Matthew Garrett <mjg59@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: David Howells <dhowells@redhat.com> Signed-off-by: James Morris <jmorris@namei.org>
This commit is contained in:
Matthew Garrett
James Morris
parent
9e47d31d6a
commit
000d388ed3
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@ -2244,6 +2244,15 @@
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lockd.nlm_udpport=M [NFS] Assign UDP port.
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Format: <integer>
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lockdown= [SECURITY]
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{ integrity | confidentiality }
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Enable the kernel lockdown feature. If set to
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integrity, kernel features that allow userland to
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modify the running kernel are disabled. If set to
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confidentiality, kernel features that allow userland
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to extract confidential information from the kernel
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are also disabled.
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locktorture.nreaders_stress= [KNL]
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Set the number of locking read-acquisition kthreads.
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Defaults to being automatically set based on the
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@ -97,6 +97,9 @@ enum lsm_event {
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* potentially a moving target. It is easy to misuse this information
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* in a way that could break userspace. Please be careful not to do
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* so.
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*
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* If you add to this, remember to extend lockdown_reasons in
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* security/lockdown/lockdown.c.
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*/
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enum lockdown_reason {
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LOCKDOWN_NONE,
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@ -237,6 +237,7 @@ source "security/apparmor/Kconfig"
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source "security/loadpin/Kconfig"
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source "security/yama/Kconfig"
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source "security/safesetid/Kconfig"
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source "security/lockdown/Kconfig"
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source "security/integrity/Kconfig"
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@ -276,11 +277,11 @@ endchoice
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config LSM
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string "Ordered list of enabled LSMs"
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default "yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if DEFAULT_SECURITY_SMACK
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default "yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if DEFAULT_SECURITY_APPARMOR
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default "yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO
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default "yama,loadpin,safesetid,integrity" if DEFAULT_SECURITY_DAC
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default "yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor"
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default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if DEFAULT_SECURITY_SMACK
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default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if DEFAULT_SECURITY_APPARMOR
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default "lockdown,yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO
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default "lockdown,yama,loadpin,safesetid,integrity" if DEFAULT_SECURITY_DAC
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default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor"
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help
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A comma-separated list of LSMs, in initialization order.
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Any LSMs left off this list will be ignored. This can be
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@ -11,6 +11,7 @@ subdir-$(CONFIG_SECURITY_APPARMOR) += apparmor
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subdir-$(CONFIG_SECURITY_YAMA) += yama
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subdir-$(CONFIG_SECURITY_LOADPIN) += loadpin
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subdir-$(CONFIG_SECURITY_SAFESETID) += safesetid
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subdir-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown
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# always enable default capabilities
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obj-y += commoncap.o
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@ -27,6 +28,7 @@ obj-$(CONFIG_SECURITY_APPARMOR) += apparmor/
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obj-$(CONFIG_SECURITY_YAMA) += yama/
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obj-$(CONFIG_SECURITY_LOADPIN) += loadpin/
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obj-$(CONFIG_SECURITY_SAFESETID) += safesetid/
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obj-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown/
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obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o
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# Object integrity file lists
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@ -0,0 +1,46 @@
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config SECURITY_LOCKDOWN_LSM
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bool "Basic module for enforcing kernel lockdown"
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depends on SECURITY
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help
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Build support for an LSM that enforces a coarse kernel lockdown
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behaviour.
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config SECURITY_LOCKDOWN_LSM_EARLY
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bool "Enable lockdown LSM early in init"
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depends on SECURITY_LOCKDOWN_LSM
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help
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Enable the lockdown LSM early in boot. This is necessary in order
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to ensure that lockdown enforcement can be carried out on kernel
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boot parameters that are otherwise parsed before the security
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subsystem is fully initialised. If enabled, lockdown will
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unconditionally be called before any other LSMs.
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choice
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prompt "Kernel default lockdown mode"
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default LOCK_DOWN_KERNEL_FORCE_NONE
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depends on SECURITY_LOCKDOWN_LSM
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help
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The kernel can be configured to default to differing levels of
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lockdown.
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config LOCK_DOWN_KERNEL_FORCE_NONE
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bool "None"
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help
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No lockdown functionality is enabled by default. Lockdown may be
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enabled via the kernel commandline or /sys/kernel/security/lockdown.
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config LOCK_DOWN_KERNEL_FORCE_INTEGRITY
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bool "Integrity"
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help
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The kernel runs in integrity mode by default. Features that allow
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the kernel to be modified at runtime are disabled.
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config LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY
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bool "Confidentiality"
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help
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The kernel runs in confidentiality mode by default. Features that
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allow the kernel to be modified at runtime or that permit userland
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code to read confidential material held inside the kernel are
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disabled.
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endchoice
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@ -0,0 +1 @@
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obj-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown.o
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@ -0,0 +1,169 @@
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// SPDX-License-Identifier: GPL-2.0
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/* Lock down the kernel
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*
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* Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#include <linux/security.h>
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#include <linux/export.h>
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#include <linux/lsm_hooks.h>
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static enum lockdown_reason kernel_locked_down;
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static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
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[LOCKDOWN_NONE] = "none",
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[LOCKDOWN_INTEGRITY_MAX] = "integrity",
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[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
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};
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static enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
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LOCKDOWN_INTEGRITY_MAX,
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LOCKDOWN_CONFIDENTIALITY_MAX};
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/*
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* Put the kernel into lock-down mode.
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*/
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static int lock_kernel_down(const char *where, enum lockdown_reason level)
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{
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if (kernel_locked_down >= level)
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return -EPERM;
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kernel_locked_down = level;
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pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
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where);
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return 0;
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}
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static int __init lockdown_param(char *level)
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{
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if (!level)
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return -EINVAL;
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if (strcmp(level, "integrity") == 0)
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lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
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else if (strcmp(level, "confidentiality") == 0)
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lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
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else
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return -EINVAL;
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return 0;
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}
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early_param("lockdown", lockdown_param);
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/**
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* lockdown_is_locked_down - Find out if the kernel is locked down
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* @what: Tag to use in notice generated if lockdown is in effect
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*/
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static int lockdown_is_locked_down(enum lockdown_reason what)
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{
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if (kernel_locked_down >= what) {
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if (lockdown_reasons[what])
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pr_notice("Lockdown: %s is restricted; see man kernel_lockdown.7\n",
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lockdown_reasons[what]);
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return -EPERM;
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}
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return 0;
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}
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static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
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LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
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};
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static int __init lockdown_lsm_init(void)
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{
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#if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
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lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
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#elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
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lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
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#endif
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security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
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"lockdown");
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return 0;
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}
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static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
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loff_t *ppos)
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{
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char temp[80];
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int i, offset = 0;
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for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
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enum lockdown_reason level = lockdown_levels[i];
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if (lockdown_reasons[level]) {
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const char *label = lockdown_reasons[level];
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if (kernel_locked_down == level)
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offset += sprintf(temp+offset, "[%s] ", label);
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else
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offset += sprintf(temp+offset, "%s ", label);
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}
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}
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/* Convert the last space to a newline if needed. */
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if (offset > 0)
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temp[offset-1] = '\n';
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return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
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}
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static ssize_t lockdown_write(struct file *file, const char __user *buf,
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size_t n, loff_t *ppos)
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{
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char *state;
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int i, len, err = -EINVAL;
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state = memdup_user_nul(buf, n);
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if (IS_ERR(state))
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return PTR_ERR(state);
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len = strlen(state);
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if (len && state[len-1] == '\n') {
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state[len-1] = '\0';
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len--;
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}
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for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
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enum lockdown_reason level = lockdown_levels[i];
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const char *label = lockdown_reasons[level];
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if (label && !strcmp(state, label))
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err = lock_kernel_down("securityfs", level);
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}
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kfree(state);
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return err ? err : n;
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}
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static const struct file_operations lockdown_ops = {
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.read = lockdown_read,
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.write = lockdown_write,
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};
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static int __init lockdown_secfs_init(void)
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{
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struct dentry *dentry;
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dentry = securityfs_create_file("lockdown", 0600, NULL, NULL,
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&lockdown_ops);
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return PTR_ERR_OR_ZERO(dentry);
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}
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core_initcall(lockdown_secfs_init);
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#ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
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DEFINE_EARLY_LSM(lockdown) = {
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#else
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DEFINE_LSM(lockdown) = {
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#endif
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.name = "lockdown",
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.init = lockdown_lsm_init,
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};
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