Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755614Ab3JCUzg (ORCPT ); Thu, 3 Oct 2013 16:55:36 -0400 Received: from smtp.outflux.net ([198.145.64.163]:57162 "EHLO smtp.outflux.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755593Ab3JCUz3 (ORCPT ); Thu, 3 Oct 2013 16:55:29 -0400 Date: Thu, 3 Oct 2013 13:55:15 -0700 From: Kees Cook To: Kees Cook Cc: James Morris , LKML , James Morris , Casey Schaufler , linux-security-module , Rusty Russell Subject: Re: [PATCH] LSM: ModPin LSM for module loading restrictions Message-ID: <20131003205515.GF5729@outflux.net> References: <20130920203556.GA8726@www.outflux.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Outflux X-HELO: www.outflux.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 13686 Lines: 378 On Mon, Sep 23, 2013 at 06:45:35PM -0700, Kees Cook wrote: > [+rusty] > > On Mon, Sep 23, 2013 at 6:28 PM, James Morris wrote: > > 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 > >> > >> Are you using this for ChromeOS? > > Yes. Chrome OS uses a read-only root filesystem that is backed by > dm-verity. This lets us pin all module loading to that filesystem > without needing per-module signatures. > > > Also, you should CC Rusty on this. > > Done! :) Ping... any feedback on this? I'd like to get this landed so I can send further patches that touch this and IMA. Thanks, -Kees > > -Kees > > > > > > >> > >> > >> > --- > >> > 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-security-module" in > >> the body of a message to majordomo@vger.kernel.org > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > >> > > > > -- > > James Morris > > > > > > -- > Kees Cook > Chrome OS Security > -- > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Kees Cook @outflux.net -- 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/