security/loadpin/loadpin.c

   1 /*
   2  * Module and Firmware Pinning Security Module
   3  *
   4  * Copyright 2011-2016 Google Inc.
   5  *
   6  * Author: Kees Cook <[email protected]>
   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 enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
  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       = "enforce",
  64                 .data           = &enforce,
  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                 char bdev[BDEVNAME_SIZE];
  88
  89                 ro = bdev_read_only(mnt_sb->s_bdev);
  90                 bdevname(mnt_sb->s_bdev, bdev);
  91                 pr_info("%s (%u:%u): %s\n", bdev,
  92                         MAJOR(mnt_sb->s_bdev->bd_dev),
  93                         MINOR(mnt_sb->s_bdev->bd_dev),
  94                         ro ? "read-only" : "writable");
  95         } else
  96                 pr_info("mnt_sb lacks block device, treating as: writable\n");
  97
  98         if (!ro) {
  99                 if (!register_sysctl_paths(loadpin_sysctl_path,
 100                                            loadpin_sysctl_table))
 101                         pr_notice("sysctl registration failed!\n");
 102                 else
 103                         pr_info("enforcement can be disabled.\n");
 104         } else
 105                 pr_info("load pinning engaged.\n");
 106 }
 107 #else
 108 static void check_pinning_enforcement(struct super_block *mnt_sb)
 109 {
 110         pr_info("load pinning engaged.\n");
 111 }
 112 #endif
 113
 114 static void loadpin_sb_free_security(struct super_block *mnt_sb)
 115 {
 116         /*
 117          * When unmounting the filesystem we were using for load
 118          * pinning, we acknowledge the superblock release, but make sure
 119          * no other modules or firmware can be loaded.
 120          */
 121         if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
 122                 pinned_root = ERR_PTR(-EIO);
 123                 pr_info("umount pinned fs: refusing further loads\n");
 124         }
 125 }
 126
 127 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
 128 {
 129         struct super_block *load_root;
 130         const char *origin = kernel_read_file_id_str(id);
 131
 132         /* This handles the older init_module API that has a NULL file. */
 133         if (!file) {
 134                 if (!enforce) {
 135                         report_load(origin, NULL, "old-api-pinning-ignored");
 136                         return 0;
 137                 }
 138
 139                 report_load(origin, NULL, "old-api-denied");
 140                 return -EPERM;
 141         }
 142
 143         load_root = file->f_path.mnt->mnt_sb;
 144
 145         /* First loaded module/firmware defines the root for all others. */
 146         spin_lock(&pinned_root_spinlock);
 147         /*
 148          * pinned_root is only NULL at startup. Otherwise, it is either
 149          * a valid reference, or an ERR_PTR.
 150          */
 151         if (!pinned_root) {
 152                 pinned_root = load_root;
 153                 /*
 154                  * Unlock now since it's only pinned_root we care about.
 155                  * In the worst case, we will (correctly) report pinning
 156                  * failures before we have announced that pinning is
 157                  * enforcing. This would be purely cosmetic.
 158                  */
 159                 spin_unlock(&pinned_root_spinlock);
 160                 check_pinning_enforcement(pinned_root);
 161                 report_load(origin, file, "pinned");
 162         } else {
 163                 spin_unlock(&pinned_root_spinlock);
 164         }
 165
 166         if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
 167                 if (unlikely(!enforce)) {
 168                         report_load(origin, file, "pinning-ignored");
 169                         return 0;
 170                 }
 171
 172                 report_load(origin, file, "denied");
 173                 return -EPERM;
 174         }
 175
 176         return 0;
 177 }
 178
 179 static int loadpin_load_data(enum kernel_load_data_id id)
 180 {
 181         return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
 182 }
 183
 184 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
 185         LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
 186         LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
 187         LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
 188 };
 189
 190 void __init loadpin_add_hooks(void)
 191 {
 192         pr_info("ready to pin (currently %senforcing)\n",
 193                 enforce ? "" : "not ");
 194         security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
 195 }
 196
 197 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
 198 module_param(enforce, int, 0);
 199 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");