text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * Module and Firmware Pinning Security Module
   *
   * Copyright 2011-2016 Google Inc.
   *
   * Author: Kees Cook <keescook@chromium.org>
   */
  
  #define pr_fmt(fmt) "LoadPin: " fmt
  
  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/lsm_hooks.h>
  #include <linux/mount.h>
  #include <linux/path.h>
  #include <linux/sched.h>	/* current */
  #include <linux/string_helpers.h>
  
  static void report_load(const char *origin, struct file *file, char *operation)
  {
  	char *cmdline, *pathname;
  
  	pathname = kstrdup_quotable_file(file, GFP_KERNEL);
  	cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
  
  	pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
  		  origin, operation,
  		  (pathname && pathname[0] != '<') ? "\"" : "",
  		  pathname,
  		  (pathname && pathname[0] != '<') ? "\"" : "",
  		  task_pid_nr(current),
  		  cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
  
  	kfree(cmdline);
  	kfree(pathname);
  }
  
  static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
  static char *exclude_read_files[READING_MAX_ID];
  static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
  static struct super_block *pinned_root;
  static DEFINE_SPINLOCK(pinned_root_spinlock);
  
  #ifdef CONFIG_SYSCTL
  
  static struct ctl_path loadpin_sysctl_path[] = {
  	{ .procname = "kernel", },
  	{ .procname = "loadpin", },
  	{ }
  };
  
  static struct ctl_table loadpin_sysctl_table[] = {
  	{
  		.procname       = "enforce",
  		.data           = &enforce,
  		.maxlen         = sizeof(int),
  		.mode           = 0644,
  		.proc_handler   = proc_dointvec_minmax,
  		.extra1         = SYSCTL_ZERO,
  		.extra2         = SYSCTL_ONE,
  	},
  	{ }
  };
  
  /*
   * This must be called after early kernel init, since then the rootdev
   * is available.
   */
  static void check_pinning_enforcement(struct super_block *mnt_sb)
  {
  	bool ro = false;
  
  	/*
  	 * If load pinning is not enforced via a read-only block
  	 * device, allow sysctl to change modes for testing.
  	 */
  	if (mnt_sb->s_bdev) {
  		char bdev[BDEVNAME_SIZE];
  
  		ro = bdev_read_only(mnt_sb->s_bdev);
  		bdevname(mnt_sb->s_bdev, bdev);
  		pr_info("%s (%u:%u): %s\n", bdev,
  			MAJOR(mnt_sb->s_bdev->bd_dev),
  			MINOR(mnt_sb->s_bdev->bd_dev),
  			ro ? "read-only" : "writable");
  	} else
  		pr_info("mnt_sb lacks block device, treating as: writable\n");
  
  	if (!ro) {
  		if (!register_sysctl_paths(loadpin_sysctl_path,
  					   loadpin_sysctl_table))
  			pr_notice("sysctl registration failed!\n");
  		else
  			pr_info("enforcement can be disabled.\n");
  	} else
  		pr_info("load pinning engaged.\n");
  }
  #else
  static void check_pinning_enforcement(struct super_block *mnt_sb)
  {
  	pr_info("load pinning engaged.\n");
  }
  #endif
  
  static void loadpin_sb_free_security(struct super_block *mnt_sb)
  {
  	/*
  	 * When unmounting the filesystem we were using for load
  	 * pinning, we acknowledge the superblock release, but make sure
  	 * no other modules or firmware can be loaded.
  	 */
  	if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
  		pinned_root = ERR_PTR(-EIO);
  		pr_info("umount pinned fs: refusing further loads\n");
  	}
  }
  
  static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
  {
  	struct super_block *load_root;
  	const char *origin = kernel_read_file_id_str(id);
  
  	/* If the file id is excluded, ignore the pinning. */
  	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
  	    ignore_read_file_id[id]) {
  		report_load(origin, file, "pinning-excluded");
  		return 0;
  	}
  
  	/* This handles the older init_module API that has a NULL file. */
  	if (!file) {
  		if (!enforce) {
  			report_load(origin, NULL, "old-api-pinning-ignored");
  			return 0;
  		}
  
  		report_load(origin, NULL, "old-api-denied");
  		return -EPERM;
  	}
  
  	load_root = file->f_path.mnt->mnt_sb;
  
  	/* First loaded module/firmware defines the root for all others. */
  	spin_lock(&pinned_root_spinlock);
  	/*
  	 * pinned_root is only NULL at startup. Otherwise, it is either
  	 * a valid reference, or an ERR_PTR.
  	 */
  	if (!pinned_root) {
  		pinned_root = load_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
  		 * enforcing. This would be purely cosmetic.
  		 */
  		spin_unlock(&pinned_root_spinlock);
  		check_pinning_enforcement(pinned_root);
  		report_load(origin, file, "pinned");
  	} else {
  		spin_unlock(&pinned_root_spinlock);
  	}
  
  	if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
  		if (unlikely(!enforce)) {
  			report_load(origin, file, "pinning-ignored");
  			return 0;
  		}
  
  		report_load(origin, file, "denied");
  		return -EPERM;
  	}
  
  	return 0;
  }
  
  static int loadpin_load_data(enum kernel_load_data_id id)
  {
  	return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
  }
  
  static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
  	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
  	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
  	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
  };
  
  static void __init parse_exclude(void)
  {
  	int i, j;
  	char *cur;
  
  	/*
  	 * Make sure all the arrays stay within expected sizes. This
  	 * is slightly weird because kernel_read_file_str[] includes
  	 * READING_MAX_ID, which isn't actually meaningful here.
  	 */
  	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
  		     ARRAY_SIZE(ignore_read_file_id));
  	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
  		     ARRAY_SIZE(ignore_read_file_id));
  
  	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
  		cur = exclude_read_files[i];
  		if (!cur)
  			break;
  		if (*cur == '\0')
  			continue;
  
  		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
  			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
  				pr_info("excluding: %s\n",
  					kernel_read_file_str[j]);
  				ignore_read_file_id[j] = 1;
  				/*
  				 * Can not break, because one read_file_str
  				 * may map to more than on read_file_id.
  				 */
  			}
  		}
  	}
  }
  
  static int __init loadpin_init(void)
  {
  	pr_info("ready to pin (currently %senforcing)\n",
  		enforce ? "" : "not ");
  	parse_exclude();
  	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
  	return 0;
  }
  
  DEFINE_LSM(loadpin) = {
  	.name = "loadpin",
  	.init = loadpin_init,
  };
  
  /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
  module_param(enforce, int, 0);
  MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
  module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
  MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
  