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![Kees Cook](/assets/img/avatar_default.png)
Instead of being enabled by default when SECURITY_LOADPIN is selected, provide an additional (default off) config to determine the boot time behavior. As before, the "loadpin.enabled=0/1" kernel parameter remains available. Suggested-by: James Morris <jmorris@namei.org> Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
190 lines
5.1 KiB
C
190 lines
5.1 KiB
C
/*
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* Module and Firmware Pinning Security Module
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*
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* Copyright 2011-2016 Google Inc.
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*
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* Author: Kees Cook <keescook@chromium.org>
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*
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* This software is licensed under the terms of the GNU General Public
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* License version 2, as published by the Free Software Foundation, and
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* may be copied, distributed, and modified under those terms.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#define pr_fmt(fmt) "LoadPin: " fmt
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/fs_struct.h>
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#include <linux/lsm_hooks.h>
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#include <linux/mount.h>
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#include <linux/path.h>
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#include <linux/sched.h> /* current */
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#include <linux/string_helpers.h>
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static void report_load(const char *origin, struct file *file, char *operation)
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{
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char *cmdline, *pathname;
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pathname = kstrdup_quotable_file(file, GFP_KERNEL);
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cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
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pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
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origin, operation,
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(pathname && pathname[0] != '<') ? "\"" : "",
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pathname,
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(pathname && pathname[0] != '<') ? "\"" : "",
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task_pid_nr(current),
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cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
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kfree(cmdline);
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kfree(pathname);
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}
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static int enabled = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENABLED);
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static struct super_block *pinned_root;
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static DEFINE_SPINLOCK(pinned_root_spinlock);
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#ifdef CONFIG_SYSCTL
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static int zero;
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static int one = 1;
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static struct ctl_path loadpin_sysctl_path[] = {
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{ .procname = "kernel", },
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{ .procname = "loadpin", },
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{ }
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};
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static struct ctl_table loadpin_sysctl_table[] = {
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{
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.procname = "enabled",
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.data = &enabled,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = proc_dointvec_minmax,
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.extra1 = &zero,
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.extra2 = &one,
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},
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{ }
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};
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/*
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* This must be called after early kernel init, since then the rootdev
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* is available.
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*/
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static void check_pinning_enforcement(struct super_block *mnt_sb)
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{
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bool ro = false;
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/*
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* If load pinning is not enforced via a read-only block
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* device, allow sysctl to change modes for testing.
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*/
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if (mnt_sb->s_bdev) {
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ro = bdev_read_only(mnt_sb->s_bdev);
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pr_info("dev(%u,%u): %s\n",
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MAJOR(mnt_sb->s_bdev->bd_dev),
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MINOR(mnt_sb->s_bdev->bd_dev),
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ro ? "read-only" : "writable");
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} else
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pr_info("mnt_sb lacks block device, treating as: writable\n");
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if (!ro) {
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if (!register_sysctl_paths(loadpin_sysctl_path,
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loadpin_sysctl_table))
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pr_notice("sysctl registration failed!\n");
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else
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pr_info("load pinning can be disabled.\n");
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} else
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pr_info("load pinning engaged.\n");
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}
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#else
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static void check_pinning_enforcement(struct super_block *mnt_sb)
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{
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pr_info("load pinning engaged.\n");
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}
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#endif
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static void loadpin_sb_free_security(struct super_block *mnt_sb)
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{
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/*
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* When unmounting the filesystem we were using for load
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* pinning, we acknowledge the superblock release, but make sure
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* no other modules or firmware can be loaded.
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*/
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if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
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pinned_root = ERR_PTR(-EIO);
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pr_info("umount pinned fs: refusing further loads\n");
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}
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}
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static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
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{
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struct super_block *load_root;
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const char *origin = kernel_read_file_id_str(id);
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/* This handles the older init_module API that has a NULL file. */
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if (!file) {
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if (!enabled) {
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report_load(origin, NULL, "old-api-pinning-ignored");
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return 0;
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}
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report_load(origin, NULL, "old-api-denied");
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return -EPERM;
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}
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load_root = file->f_path.mnt->mnt_sb;
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/* First loaded module/firmware defines the root for all others. */
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spin_lock(&pinned_root_spinlock);
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/*
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* pinned_root is only NULL at startup. Otherwise, it is either
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* a valid reference, or an ERR_PTR.
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*/
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if (!pinned_root) {
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pinned_root = load_root;
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/*
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* Unlock now since it's only pinned_root we care about.
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* In the worst case, we will (correctly) report pinning
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* failures before we have announced that pinning is
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* enabled. This would be purely cosmetic.
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*/
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spin_unlock(&pinned_root_spinlock);
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check_pinning_enforcement(pinned_root);
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report_load(origin, file, "pinned");
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} else {
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spin_unlock(&pinned_root_spinlock);
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}
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if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
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if (unlikely(!enabled)) {
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report_load(origin, file, "pinning-ignored");
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return 0;
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}
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report_load(origin, file, "denied");
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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 loadpin_hooks[] = {
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LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
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LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
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};
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void __init loadpin_add_hooks(void)
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{
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pr_info("ready to pin (currently %sabled)", enabled ? "en" : "dis");
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security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks));
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}
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/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
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module_param(enabled, int, 0);
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MODULE_PARM_DESC(enabled, "Pin module/firmware loading (default: true)");
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