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Date: Tue, 24 Sep 2013 11:28:57 +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 Tue, 24 Sep 2013, James Morris wrote:
> 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?
Also, you should CC Rusty on this.
>
>
> > ---
> > 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
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at http://www.tux.org/lkml/
> >
>
> --
> James Morris
> <jmorris@...ei.org>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
--
James Morris
<jmorris@...ei.org>
--
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