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![Kees Cook](/assets/img/avatar_default.png)
As with the kernel_load_data LSM hook, add a "contents" flag to the kernel_read_file LSM hook that indicates whether the LSM can expect a matching call to the kernel_post_read_file LSM hook with the full contents of the file. With the coming addition of partial file read support for kernel_read_file*() API, the LSM will no longer be able to always see the entire contents of a file during the read calls. For cases where the LSM must read examine the complete file contents, it will need to do so on its own every time the kernel_read_file hook is called with contents=false (or reject such cases). Adjust all existing LSMs to retain existing behavior. Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com> Link: https://lore.kernel.org/r/20201002173828.2099543-12-keescook@chromium.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
255 lines
6.7 KiB
C
255 lines
6.7 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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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_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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char bdev[BDEVNAME_SIZE];
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ro = bdev_read_only(mnt_sb->s_bdev);
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bdevname(mnt_sb->s_bdev, bdev);
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pr_info("%s (%u:%u): %s\n", 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) || load_root != pinned_root) {
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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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/* 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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