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Message-ID: <alpine.LRH.2.02.1309241124420.3782@tundra.namei.org>
Date: Tue, 24 Sep 2013 11:24:57 +1000 (EST)
From: James Morris <jmorris@...ei.org>
To: Kees Cook <keescook@...omium.org>
cc: linux-kernel@...r.kernel.org,
James Morris <james.l.morris@...cle.com>,
Casey Schaufler <casey@...aufler-ca.com>,
linux-security-module@...r.kernel.org
Subject: Re: [PATCH] LSM: ModPin LSM for module loading restrictions
On Fri, 20 Sep 2013, Kees Cook wrote:
> This LSM enforces that modules must all come from the same filesystem,
> with the expectation that such a filesystem is backed by a read-only
> device such as dm-verity or CDROM. This allows systems that have a
> verified or unchanging filesystem to enforce module loading restrictions
> without needing to sign the modules individually.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
Are you using this for ChromeOS?
> ---
> security/Kconfig | 6 ++
> security/Makefile | 2 +
> security/modpin/Kconfig | 9 +++
> security/modpin/Makefile | 1 +
> security/modpin/modpin.c | 197 ++++++++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 215 insertions(+)
> create mode 100644 security/modpin/Kconfig
> create mode 100644 security/modpin/Makefile
> create mode 100644 security/modpin/modpin.c
>
> diff --git a/security/Kconfig b/security/Kconfig
> index e9c6ac7..80172fd 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -121,6 +121,7 @@ source security/selinux/Kconfig
> source security/smack/Kconfig
> source security/tomoyo/Kconfig
> source security/apparmor/Kconfig
> +source security/modpin/Kconfig
> source security/yama/Kconfig
>
> source security/integrity/Kconfig
> @@ -131,6 +132,7 @@ choice
> default DEFAULT_SECURITY_SMACK if SECURITY_SMACK
> default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO
> default DEFAULT_SECURITY_APPARMOR if SECURITY_APPARMOR
> + default DEFAULT_SECURITY_MODPIN if SECURITY_MODPIN
> default DEFAULT_SECURITY_YAMA if SECURITY_YAMA
> default DEFAULT_SECURITY_DAC
>
> @@ -150,6 +152,9 @@ choice
> config DEFAULT_SECURITY_APPARMOR
> bool "AppArmor" if SECURITY_APPARMOR=y
>
> + config DEFAULT_SECURITY_MODPIN
> + bool "ModPin" if SECURITY_MODPIN=y
> +
> config DEFAULT_SECURITY_YAMA
> bool "Yama" if SECURITY_YAMA=y
>
> @@ -164,6 +169,7 @@ config DEFAULT_SECURITY
> default "smack" if DEFAULT_SECURITY_SMACK
> default "tomoyo" if DEFAULT_SECURITY_TOMOYO
> default "apparmor" if DEFAULT_SECURITY_APPARMOR
> + default "modpin" if DEFAULT_SECURITY_MODPIN
> default "yama" if DEFAULT_SECURITY_YAMA
> default "" if DEFAULT_SECURITY_DAC
>
> diff --git a/security/Makefile b/security/Makefile
> index c26c81e..73d0a05 100644
> --- a/security/Makefile
> +++ b/security/Makefile
> @@ -7,6 +7,7 @@ subdir-$(CONFIG_SECURITY_SELINUX) += selinux
> subdir-$(CONFIG_SECURITY_SMACK) += smack
> subdir-$(CONFIG_SECURITY_TOMOYO) += tomoyo
> subdir-$(CONFIG_SECURITY_APPARMOR) += apparmor
> +subdir-$(CONFIG_SECURITY_MODPIN) += modpin
> subdir-$(CONFIG_SECURITY_YAMA) += yama
>
> # always enable default capabilities
> @@ -22,6 +23,7 @@ obj-$(CONFIG_SECURITY_SMACK) += smack/built-in.o
> obj-$(CONFIG_AUDIT) += lsm_audit.o
> obj-$(CONFIG_SECURITY_TOMOYO) += tomoyo/built-in.o
> obj-$(CONFIG_SECURITY_APPARMOR) += apparmor/built-in.o
> +obj-$(CONFIG_SECURITY_MODPIN) += modpin/built-in.o
> obj-$(CONFIG_SECURITY_YAMA) += yama/built-in.o
> obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o
>
> diff --git a/security/modpin/Kconfig b/security/modpin/Kconfig
> new file mode 100644
> index 0000000..5be9dd5
> --- /dev/null
> +++ b/security/modpin/Kconfig
> @@ -0,0 +1,9 @@
> +config SECURITY_MODPIN
> + bool "Module filesystem origin pinning"
> + depends on SECURITY
> + help
> + Module loading will be pinned to the first filesystem used for
> + loading. Any modules that come from other filesystems will be
> + rejected. This is best used on systems without an initrd that
> + have a root filesystem backed by a read-only device such as
> + dm-verity or a CDROM.
> diff --git a/security/modpin/Makefile b/security/modpin/Makefile
> new file mode 100644
> index 0000000..9080b29
> --- /dev/null
> +++ b/security/modpin/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_SECURITY_MODPIN) += modpin.o
> diff --git a/security/modpin/modpin.c b/security/modpin/modpin.c
> new file mode 100644
> index 0000000..107b4d8
> --- /dev/null
> +++ b/security/modpin/modpin.c
> @@ -0,0 +1,197 @@
> +/*
> + * Module Pinning Security Module
> + *
> + * Copyright 2011-2013 Google Inc.
> + *
> + * Authors:
> + * Kees Cook <keescook@...omium.org>
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#define pr_fmt(fmt) "ModPin LSM: " fmt
> +
> +#include <linux/module.h>
> +#include <linux/security.h>
> +#include <linux/sched.h>
> +#include <linux/fs.h>
> +#include <linux/fs_struct.h>
> +#include <linux/mount.h>
> +#include <linux/path.h>
> +#include <linux/root_dev.h>
> +
> +static void report_load_module(struct path *path, char *operation)
> +{
> + char *alloced = NULL;
> + char *pathname; /* Pointer to either static string or "alloced". */
> +
> + if (!path)
> + pathname = "<unknown>";
> + else {
> + /* We will allow 11 spaces for ' (deleted)' to be appended */
> + alloced = pathname = kmalloc(PATH_MAX+11, GFP_KERNEL);
> + if (!pathname)
> + pathname = "<no_memory>";
> + else {
> + pathname = d_path(path, pathname, PATH_MAX+11);
> + if (IS_ERR(pathname))
> + pathname = "<too_long>";
> + }
> + }
> +
> + pr_notice("init_module %s module=%s pid=%d\n",
> + operation, pathname, task_pid_nr(current));
> +
> + kfree(alloced);
> +}
> +
> +static int modpin_enforced = 1;
> +static struct dentry *pinned_root;
> +static DEFINE_SPINLOCK(pinned_root_spinlock);
> +
> +#ifdef CONFIG_SYSCTL
> +static int zero;
> +static int one = 1;
> +
> +static struct ctl_path modpin_sysctl_path[] = {
> + { .procname = "kernel", },
> + { .procname = "modpin", },
> + { }
> +};
> +
> +static struct ctl_table modpin_sysctl_table[] = {
> + {
> + .procname = "enforced",
> + .data = &modpin_enforced,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = &zero,
> + .extra2 = &one,
> + },
> + { }
> +};
> +
> +/*
> + * Check if the root device is read-only (e.g. dm-verity is enabled).
> + * This must be called after early kernel init, since only then is the
> + * rootdev available.
> + */
> +static bool rootdev_readonly(void)
> +{
> + bool rc;
> + struct block_device *bdev;
> + const fmode_t mode = FMODE_WRITE;
> +
> + bdev = blkdev_get_by_dev(ROOT_DEV, mode, NULL);
> + if (IS_ERR(bdev)) {
> + /* In this weird case, assume it is read-only. */
> + pr_info("dev(%u,%u): FMODE_WRITE disallowed?!\n",
> + MAJOR(ROOT_DEV), MINOR(ROOT_DEV));
> + return true;
> + }
> +
> + rc = bdev_read_only(bdev);
> + blkdev_put(bdev, mode);
> +
> + pr_info("dev(%u,%u): %s\n", MAJOR(ROOT_DEV), MINOR(ROOT_DEV),
> + rc ? "read-only" : "writable");
> +
> + return rc;
> +}
> +
> +static void check_pinning_enforcement(void)
> +{
> + /*
> + * If module pinning is not being enforced, allow sysctl to change
> + * modes for testing.
> + */
> + if (!rootdev_readonly()) {
> + if (!register_sysctl_paths(modpin_sysctl_path,
> + modpin_sysctl_table))
> + pr_notice("sysctl registration failed!\n");
> + else
> + pr_info("module pinning can be disabled.\n");
> + } else
> + pr_info("module pinning engaged.\n");
> +}
> +#else
> +static void check_pinning_enforcement(void) { }
> +#endif
> +
> +
> +static int modpin_load_module(struct file *file)
> +{
> + struct dentry *module_root;
> +
> + if (!file) {
> + if (!modpin_enforced) {
> + report_load_module(NULL, "old-api-pinning-ignored");
> + return 0;
> + }
> +
> + report_load_module(NULL, "old-api-denied");
> + return -EPERM;
> + }
> +
> + module_root = file->f_path.mnt->mnt_root;
> +
> + /* First loaded module defines the root for all others. */
> + spin_lock(&pinned_root_spinlock);
> + if (!pinned_root) {
> + pinned_root = dget(module_root);
> + /*
> + * Unlock now since it's only pinned_root we care about.
> + * In the worst case, we will (correctly) report pinning
> + * failures before we have announced that pinning is
> + * enabled. This would be purely cosmetic.
> + */
> + spin_unlock(&pinned_root_spinlock);
> + check_pinning_enforcement();
> + report_load_module(&file->f_path, "pinned");
> + return 0;
> + }
> + spin_unlock(&pinned_root_spinlock);
> +
> + if (module_root != pinned_root) {
> + if (unlikely(!modpin_enforced)) {
> + report_load_module(&file->f_path, "pinning-ignored");
> + return 0;
> + }
> +
> + report_load_module(&file->f_path, "denied");
> + return -EPERM;
> + }
> +
> + return 0;
> +}
> +
> +static struct security_operations modpin_ops = {
> + .name = "modpin",
> + .kernel_module_from_file = modpin_load_module,
> +};
> +
> +static int __init modpin_init(void)
> +{
> + int error;
> +
> + error = register_security(&modpin_ops);
> +
> + if (error)
> + panic("Could not register ModPin security module");
> +
> + pr_info("ready to pin.\n");
> +
> + return error;
> +}
> +security_initcall(modpin_init);
> +
> +module_param(modpin_enforced, int, S_IRUSR);
> +MODULE_PARM_DESC(modpin_enforced, "Module pinning enforced (default: true)");
> --
> 1.7.9.5
>
>
> --
> Kees Cook
> Chrome OS Security
> --
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>
--
James Morris
<jmorris@...ei.org>
--
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