416 строки
10 KiB
C
416 строки
10 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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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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#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/kernel_read_file.h>
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#include <linux/lsm_hooks.h>
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#include <linux/mount.h>
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#include <linux/blkdev.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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#include <linux/dm-verity-loadpin.h>
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#include <uapi/linux/loadpin.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 enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
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static char *exclude_read_files[READING_MAX_ID];
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static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
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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_SECURITY_LOADPIN_VERITY
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static bool deny_reading_verity_digests;
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#endif
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#ifdef CONFIG_SYSCTL
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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 = "enforce",
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.data = &enforce,
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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 = SYSCTL_ZERO,
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.extra2 = SYSCTL_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("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
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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("enforcement 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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bool contents)
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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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/*
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* If we will not know that we'll be seeing the full contents
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* then we cannot trust a load will be complete and unchanged
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* off disk. Treat all contents=false hooks as if there were
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* no associated file struct.
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*/
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if (!contents)
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file = NULL;
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/* If the file id is excluded, ignore the pinning. */
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if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
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ignore_read_file_id[id]) {
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report_load(origin, file, "pinning-excluded");
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return 0;
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}
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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 (!enforce) {
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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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* enforcing. 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) ||
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((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
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if (unlikely(!enforce)) {
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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 int loadpin_load_data(enum kernel_load_data_id id, bool contents)
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{
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return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents);
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}
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static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
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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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LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
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};
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static void __init parse_exclude(void)
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{
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int i, j;
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char *cur;
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/*
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* Make sure all the arrays stay within expected sizes. This
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* is slightly weird because kernel_read_file_str[] includes
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* READING_MAX_ID, which isn't actually meaningful here.
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*/
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BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
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ARRAY_SIZE(ignore_read_file_id));
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BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
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ARRAY_SIZE(ignore_read_file_id));
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for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
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cur = exclude_read_files[i];
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if (!cur)
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break;
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if (*cur == '\0')
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continue;
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for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
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if (strcmp(cur, kernel_read_file_str[j]) == 0) {
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pr_info("excluding: %s\n",
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kernel_read_file_str[j]);
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ignore_read_file_id[j] = 1;
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/*
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* Can not break, because one read_file_str
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* may map to more than on read_file_id.
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*/
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}
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}
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}
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}
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static int __init loadpin_init(void)
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{
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pr_info("ready to pin (currently %senforcing)\n",
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enforce ? "" : "not ");
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parse_exclude();
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security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
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return 0;
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}
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DEFINE_LSM(loadpin) = {
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.name = "loadpin",
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.init = loadpin_init,
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};
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#ifdef CONFIG_SECURITY_LOADPIN_VERITY
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enum loadpin_securityfs_interface_index {
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LOADPIN_DM_VERITY,
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};
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static int read_trusted_verity_root_digests(unsigned int fd)
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{
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struct fd f;
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void *data;
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int rc;
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char *p, *d;
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if (deny_reading_verity_digests)
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return -EPERM;
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/* The list of trusted root digests can only be set up once */
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if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
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return -EPERM;
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f = fdget(fd);
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if (!f.file)
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return -EINVAL;
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data = kzalloc(SZ_4K, GFP_KERNEL);
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if (!data) {
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rc = -ENOMEM;
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goto err;
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}
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rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
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if (rc < 0)
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goto err;
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p = data;
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p[rc] = '\0';
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p = strim(p);
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p = strim(data);
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while ((d = strsep(&p, "\n")) != NULL) {
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int len = strlen(d);
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struct dm_verity_loadpin_trusted_root_digest *trd;
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if (len % 2) {
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rc = -EPROTO;
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goto err;
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}
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len /= 2;
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trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
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if (!trd) {
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rc = -ENOMEM;
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goto err;
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}
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if (hex2bin(trd->data, d, len)) {
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kfree(trd);
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rc = -EPROTO;
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goto err;
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}
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trd->len = len;
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list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
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}
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if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
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rc = -EPROTO;
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goto err;
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}
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kfree(data);
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fdput(f);
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return 0;
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err:
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kfree(data);
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/* any failure in loading/parsing invalidates the entire list */
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{
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struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
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list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
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list_del(&trd->node);
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kfree(trd);
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}
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}
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/* disallow further attempts after reading a corrupt/invalid file */
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deny_reading_verity_digests = true;
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fdput(f);
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return rc;
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}
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/******************************** securityfs ********************************/
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static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
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{
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void __user *uarg = (void __user *)arg;
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unsigned int fd;
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switch (cmd) {
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case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
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if (copy_from_user(&fd, uarg, sizeof(fd)))
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return -EFAULT;
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return read_trusted_verity_root_digests(fd);
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default:
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return -EINVAL;
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}
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}
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static const struct file_operations loadpin_dm_verity_ops = {
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.unlocked_ioctl = dm_verity_ioctl,
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.compat_ioctl = compat_ptr_ioctl,
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};
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/**
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* init_loadpin_securityfs - create the securityfs directory for LoadPin
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*
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* We can not put this method normally under the loadpin_init() code path since
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* the security subsystem gets initialized before the vfs caches.
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*
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* Returns 0 if the securityfs directory creation was successful.
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*/
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static int __init init_loadpin_securityfs(void)
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{
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struct dentry *loadpin_dir, *dentry;
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loadpin_dir = securityfs_create_dir("loadpin", NULL);
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if (IS_ERR(loadpin_dir)) {
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pr_err("LoadPin: could not create securityfs dir: %ld\n",
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PTR_ERR(loadpin_dir));
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return PTR_ERR(loadpin_dir);
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}
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dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
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(void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
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if (IS_ERR(dentry)) {
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pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
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PTR_ERR(dentry));
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return PTR_ERR(dentry);
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}
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return 0;
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}
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fs_initcall(init_loadpin_securityfs);
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#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
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/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
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module_param(enforce, int, 0);
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MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
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module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
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MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
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