security/loadpin/loadpin.c

   1 /*
   2  * Module and Firmware Pinning Security Module
   3  *
   4  * Copyright 2011-2016 Google Inc.
   5  *
   6  * Author: Kees Cook <keescook@chromium.org>
   7  *
   8  * This software is licensed under the terms of the GNU General Public
   9  * License version 2, as published by the Free Software Foundation, and
  10  * may be copied, distributed, and modified under those terms.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  */
  17
  18 #define pr_fmt(fmt) "LoadPin: " fmt
  19
  20 #include <linux/module.h>
  21 #include <linux/fs.h>
  22 #include <linux/lsm_hooks.h>
  23 #include <linux/mount.h>
  24 #include <linux/path.h>
  25 #include <linux/sched.h>        /* current */
  26 #include <linux/string_helpers.h>
  27
  28 static void report_load(const char *origin, struct file *file, char *operation)
  29 {
  30         char *cmdline, *pathname;
  31
  32         pathname = kstrdup_quotable_file(file, GFP_KERNEL);
  33         cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
  34
  35         pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
  36                   origin, operation,
  37                   (pathname && pathname[0] != '<') ? "\"" : "",
  38                   pathname,
  39                   (pathname && pathname[0] != '<') ? "\"" : "",
  40                   task_pid_nr(current),
  41                   cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
  42
  43         kfree(cmdline);
  44         kfree(pathname);
  45 }
  46
  47 static int enabled = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENABLED);
  48 static struct super_block *pinned_root;
  49 static DEFINE_SPINLOCK(pinned_root_spinlock);
  50
  51 #ifdef CONFIG_SYSCTL
  52 static int zero;
  53 static int one = 1;
  54
  55 static struct ctl_path loadpin_sysctl_path[] = {
  56         { .procname = "kernel", },
  57         { .procname = "loadpin", },
  58         { }
  59 };
  60
  61 static struct ctl_table loadpin_sysctl_table[] = {
  62         {
  63                 .procname       = "enabled",
  64                 .data           = &enabled,
  65                 .maxlen         = sizeof(int),
  66                 .mode           = 0644,
  67                 .proc_handler   = proc_dointvec_minmax,
  68                 .extra1         = &zero,
  69                 .extra2         = &one,
  70         },
  71         { }
  72 };
  73
  74 /*
  75  * This must be called after early kernel init, since then the rootdev
  76  * is available.
  77  */
  78 static void check_pinning_enforcement(struct super_block *mnt_sb)
  79 {
  80         bool ro = false;
  81
  82         /*
  83          * If load pinning is not enforced via a read-only block
  84          * device, allow sysctl to change modes for testing.
  85          */
  86         if (mnt_sb->s_bdev) {
  87                 ro = bdev_read_only(mnt_sb->s_bdev);
  88                 pr_info("dev(%u,%u): %s\n",
  89                         MAJOR(mnt_sb->s_bdev->bd_dev),
  90                         MINOR(mnt_sb->s_bdev->bd_dev),
  91                         ro ? "read-only" : "writable");
  92         } else
  93                 pr_info("mnt_sb lacks block device, treating as: writable\n");
  94
  95         if (!ro) {
  96                 if (!register_sysctl_paths(loadpin_sysctl_path,
  97                                            loadpin_sysctl_table))
  98                         pr_notice("sysctl registration failed!\n");
  99                 else
 100                         pr_info("load pinning can be disabled.\n");
 101         } else
 102                 pr_info("load pinning engaged.\n");
 103 }
 104 #else
 105 static void check_pinning_enforcement(struct super_block *mnt_sb)
 106 {
 107         pr_info("load pinning engaged.\n");
 108 }
 109 #endif
 110
 111 static void loadpin_sb_free_security(struct super_block *mnt_sb)
 112 {
 113         /*
 114          * When unmounting the filesystem we were using for load
 115          * pinning, we acknowledge the superblock release, but make sure
 116          * no other modules or firmware can be loaded.
 117          */
 118         if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
 119                 pinned_root = ERR_PTR(-EIO);
 120                 pr_info("umount pinned fs: refusing further loads\n");
 121         }
 122 }
 123
 124 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
 125 {
 126         struct super_block *load_root;
 127         const char *origin = kernel_read_file_id_str(id);
 128
 129         /* This handles the older init_module API that has a NULL file. */
 130         if (!file) {
 131                 if (!enabled) {
 132                         report_load(origin, NULL, "old-api-pinning-ignored");
 133                         return 0;
 134                 }
 135
 136                 report_load(origin, NULL, "old-api-denied");
 137                 return -EPERM;
 138         }
 139
 140         load_root = file->f_path.mnt->mnt_sb;
 141
 142         /* First loaded module/firmware defines the root for all others. */
 143         spin_lock(&pinned_root_spinlock);
 144         /*
 145          * pinned_root is only NULL at startup. Otherwise, it is either
 146          * a valid reference, or an ERR_PTR.
 147          */
 148         if (!pinned_root) {
 149                 pinned_root = load_root;
 150                 /*
 151                  * Unlock now since it's only pinned_root we care about.
 152                  * In the worst case, we will (correctly) report pinning
 153                  * failures before we have announced that pinning is
 154                  * enabled. This would be purely cosmetic.
 155                  */
 156                 spin_unlock(&pinned_root_spinlock);
 157                 check_pinning_enforcement(pinned_root);
 158                 report_load(origin, file, "pinned");
 159         } else {
 160                 spin_unlock(&pinned_root_spinlock);
 161         }
 162
 163         if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
 164                 if (unlikely(!enabled)) {
 165                         report_load(origin, file, "pinning-ignored");
 166                         return 0;
 167                 }
 168
 169                 report_load(origin, file, "denied");
 170                 return -EPERM;
 171         }
 172
 173         return 0;
 174 }
 175
 176 static int loadpin_load_data(enum kernel_load_data_id id)
 177 {
 178         return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
 179 }
 180
 181 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
 182         LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
 183         LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
 184         LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
 185 };
 186
 187 void __init loadpin_add_hooks(void)
 188 {
 189         pr_info("ready to pin (currently %sabled)", enabled ? "en" : "dis");
 190         security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
 191 }
 192
 193 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
 194 module_param(enabled, int, 0);
 195 MODULE_PARM_DESC(enabled, "Pin module/firmware loading (default: true)");