Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753713Ab3IXBXR (ORCPT ); Mon, 23 Sep 2013 21:23:17 -0400 Received: from tundra.namei.org ([65.99.196.166]:33044 "EHLO tundra.namei.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753202Ab3IXBXP (ORCPT ); Mon, 23 Sep 2013 21:23:15 -0400 Date: Tue, 24 Sep 2013 11:24:57 +1000 (EST) From: James Morris To: Kees Cook cc: linux-kernel@vger.kernel.org, James Morris , Casey Schaufler , linux-security-module@vger.kernel.org Subject: Re: [PATCH] LSM: ModPin LSM for module loading restrictions In-Reply-To: <20130920203556.GA8726@www.outflux.net> Message-ID: References: <20130920203556.GA8726@www.outflux.net> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10020 Lines: 329 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 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 > + * > + * 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 > +#include > +#include > +#include > +#include > +#include > +#include > +#include > + > +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 = ""; > + else { > + /* We will allow 11 spaces for ' (deleted)' to be appended */ > + alloced = pathname = kmalloc(PATH_MAX+11, GFP_KERNEL); > + if (!pathname) > + pathname = ""; > + else { > + pathname = d_path(path, pathname, PATH_MAX+11); > + if (IS_ERR(pathname)) > + pathname = ""; > + } > + } > + > + 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@vger.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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/