security/loadpin/loadpin.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Module and Firmware Pinning Security Module
   4  *
   5  * Copyright 2011-2016 Google Inc.
   6  *
   7  * Author: Kees Cook <keescook@chromium.org>
   8  */
   9
  10 #define pr_fmt(fmt) "LoadPin: " fmt
  11
  12 #include <linux/module.h>
  13 #include <linux/fs.h>
  14 #include <linux/kernel_read_file.h>
  15 #include <linux/lsm_hooks.h>
  16 #include <linux/mount.h>
  17 #include <linux/blkdev.h>
  18 #include <linux/path.h>
  19 #include <linux/sched.h>        /* current */
  20 #include <linux/string_helpers.h>
  21 #include <linux/dm-verity-loadpin.h>
  22 #include <uapi/linux/loadpin.h>
  23
  24 #define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS"
  25
  26 static void report_load(const char *origin, struct file *file, char *operation)
  27 {
  28         char *cmdline, *pathname;
  29
  30         pathname = kstrdup_quotable_file(file, GFP_KERNEL);
  31         cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
  32
  33         pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
  34                   origin, operation,
  35                   (pathname && pathname[0] != '<') ? "\"" : "",
  36                   pathname,
  37                   (pathname && pathname[0] != '<') ? "\"" : "",
  38                   task_pid_nr(current),
  39                   cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
  40
  41         kfree(cmdline);
  42         kfree(pathname);
  43 }
  44
  45 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
  46 static char *exclude_read_files[READING_MAX_ID];
  47 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
  48 static struct super_block *pinned_root;
  49 static DEFINE_SPINLOCK(pinned_root_spinlock);
  50 #ifdef CONFIG_SECURITY_LOADPIN_VERITY
  51 static bool deny_reading_verity_digests;
  52 #endif
  53
  54 #ifdef CONFIG_SYSCTL
  55
  56 static struct ctl_path loadpin_sysctl_path[] = {
  57         { .procname = "kernel", },
  58         { .procname = "loadpin", },
  59         { }
  60 };
  61
  62 static struct ctl_table loadpin_sysctl_table[] = {
  63         {
  64                 .procname       = "enforce",
  65                 .data           = &enforce,
  66                 .maxlen         = sizeof(int),
  67                 .mode           = 0644,
  68                 .proc_handler   = proc_dointvec_minmax,
  69                 .extra1         = SYSCTL_ZERO,
  70                 .extra2         = SYSCTL_ONE,
  71         },
  72         { }
  73 };
  74
  75 /*
  76  * This must be called after early kernel init, since then the rootdev
  77  * is available.
  78  */
  79 static void check_pinning_enforcement(struct super_block *mnt_sb)
  80 {
  81         bool ro = false;
  82
  83         /*
  84          * If load pinning is not enforced via a read-only block
  85          * device, allow sysctl to change modes for testing.
  86          */
  87         if (mnt_sb->s_bdev) {
  88                 ro = bdev_read_only(mnt_sb->s_bdev);
  89                 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
  90                         MAJOR(mnt_sb->s_bdev->bd_dev),
  91                         MINOR(mnt_sb->s_bdev->bd_dev),
  92                         ro ? "read-only" : "writable");
  93         } else
  94                 pr_info("mnt_sb lacks block device, treating as: writable\n");
  95
  96         if (!ro) {
  97                 if (!register_sysctl_paths(loadpin_sysctl_path,
  98                                            loadpin_sysctl_table))
  99                         pr_notice("sysctl registration failed!\n");
 100                 else
 101                         pr_info("enforcement can be disabled.\n");
 102         } else
 103                 pr_info("load pinning engaged.\n");
 104 }
 105 #else
 106 static void check_pinning_enforcement(struct super_block *mnt_sb)
 107 {
 108         pr_info("load pinning engaged.\n");
 109 }
 110 #endif
 111
 112 static void loadpin_sb_free_security(struct super_block *mnt_sb)
 113 {
 114         /*
 115          * When unmounting the filesystem we were using for load
 116          * pinning, we acknowledge the superblock release, but make sure
 117          * no other modules or firmware can be loaded.
 118          */
 119         if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
 120                 pinned_root = ERR_PTR(-EIO);
 121                 pr_info("umount pinned fs: refusing further loads\n");
 122         }
 123 }
 124
 125 static int loadpin_check(struct file *file, enum kernel_read_file_id id)
 126 {
 127         struct super_block *load_root;
 128         const char *origin = kernel_read_file_id_str(id);
 129
 130         /* If the file id is excluded, ignore the pinning. */
 131         if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
 132             ignore_read_file_id[id]) {
 133                 report_load(origin, file, "pinning-excluded");
 134                 return 0;
 135         }
 136
 137         /* This handles the older init_module API that has a NULL file. */
 138         if (!file) {
 139                 if (!enforce) {
 140                         report_load(origin, NULL, "old-api-pinning-ignored");
 141                         return 0;
 142                 }
 143
 144                 report_load(origin, NULL, "old-api-denied");
 145                 return -EPERM;
 146         }
 147
 148         load_root = file->f_path.mnt->mnt_sb;
 149
 150         /* First loaded module/firmware defines the root for all others. */
 151         spin_lock(&pinned_root_spinlock);
 152         /*
 153          * pinned_root is only NULL at startup. Otherwise, it is either
 154          * a valid reference, or an ERR_PTR.
 155          */
 156         if (!pinned_root) {
 157                 pinned_root = load_root;
 158                 /*
 159                  * Unlock now since it's only pinned_root we care about.
 160                  * In the worst case, we will (correctly) report pinning
 161                  * failures before we have announced that pinning is
 162                  * enforcing. This would be purely cosmetic.
 163                  */
 164                 spin_unlock(&pinned_root_spinlock);
 165                 check_pinning_enforcement(pinned_root);
 166                 report_load(origin, file, "pinned");
 167         } else {
 168                 spin_unlock(&pinned_root_spinlock);
 169         }
 170
 171         if (IS_ERR_OR_NULL(pinned_root) ||
 172             ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
 173                 if (unlikely(!enforce)) {
 174                         report_load(origin, file, "pinning-ignored");
 175                         return 0;
 176                 }
 177
 178                 report_load(origin, file, "denied");
 179                 return -EPERM;
 180         }
 181
 182         return 0;
 183 }
 184
 185 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
 186                              bool contents)
 187 {
 188         /*
 189          * LoadPin only cares about the _origin_ of a file, not its
 190          * contents, so we can ignore the "are full contents available"
 191          * argument here.
 192          */
 193         return loadpin_check(file, id);
 194 }
 195
 196 static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
 197 {
 198         /*
 199          * LoadPin only cares about the _origin_ of a file, not its
 200          * contents, so a NULL file is passed, and we can ignore the
 201          * state of "contents".
 202          */
 203         return loadpin_check(NULL, (enum kernel_read_file_id) id);
 204 }
 205
 206 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
 207         LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
 208         LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
 209         LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
 210 };
 211
 212 static void __init parse_exclude(void)
 213 {
 214         int i, j;
 215         char *cur;
 216
 217         /*
 218          * Make sure all the arrays stay within expected sizes. This
 219          * is slightly weird because kernel_read_file_str[] includes
 220          * READING_MAX_ID, which isn't actually meaningful here.
 221          */
 222         BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
 223                      ARRAY_SIZE(ignore_read_file_id));
 224         BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
 225                      ARRAY_SIZE(ignore_read_file_id));
 226
 227         for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
 228                 cur = exclude_read_files[i];
 229                 if (!cur)
 230                         break;
 231                 if (*cur == '\0')
 232                         continue;
 233
 234                 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
 235                         if (strcmp(cur, kernel_read_file_str[j]) == 0) {
 236                                 pr_info("excluding: %s\n",
 237                                         kernel_read_file_str[j]);
 238                                 ignore_read_file_id[j] = 1;
 239                                 /*
 240                                  * Can not break, because one read_file_str
 241                                  * may map to more than on read_file_id.
 242                                  */
 243                         }
 244                 }
 245         }
 246 }
 247
 248 static int __init loadpin_init(void)
 249 {
 250         pr_info("ready to pin (currently %senforcing)\n",
 251                 enforce ? "" : "not ");
 252         parse_exclude();
 253         security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
 254
 255         return 0;
 256 }
 257
 258 DEFINE_LSM(loadpin) = {
 259         .name = "loadpin",
 260         .init = loadpin_init,
 261 };
 262
 263 #ifdef CONFIG_SECURITY_LOADPIN_VERITY
 264
 265 enum loadpin_securityfs_interface_index {
 266         LOADPIN_DM_VERITY,
 267 };
 268
 269 static int read_trusted_verity_root_digests(unsigned int fd)
 270 {
 271         struct fd f;
 272         void *data;
 273         int rc;
 274         char *p, *d;
 275
 276         if (deny_reading_verity_digests)
 277                 return -EPERM;
 278
 279         /* The list of trusted root digests can only be set up once */
 280         if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
 281                 return -EPERM;
 282
 283         f = fdget(fd);
 284         if (!f.file)
 285                 return -EINVAL;
 286
 287         data = kzalloc(SZ_4K, GFP_KERNEL);
 288         if (!data) {
 289                 rc = -ENOMEM;
 290                 goto err;
 291         }
 292
 293         rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
 294         if (rc < 0)
 295                 goto err;
 296
 297         p = data;
 298         p[rc] = '\0';
 299         p = strim(p);
 300
 301         p = strim(data);
 302         while ((d = strsep(&p, "\n")) != NULL) {
 303                 int len;
 304                 struct dm_verity_loadpin_trusted_root_digest *trd;
 305
 306                 if (d == data) {
 307                         /* first line, validate header */
 308                         if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
 309                                 rc = -EPROTO;
 310                                 goto err;
 311                         }
 312
 313                         continue;
 314                 }
 315
 316                 len = strlen(d);
 317
 318                 if (len % 2) {
 319                         rc = -EPROTO;
 320                         goto err;
 321                 }
 322
 323                 len /= 2;
 324
 325                 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
 326                 if (!trd) {
 327                         rc = -ENOMEM;
 328                         goto err;
 329                 }
 330
 331                 if (hex2bin(trd->data, d, len)) {
 332                         kfree(trd);
 333                         rc = -EPROTO;
 334                         goto err;
 335                 }
 336
 337                 trd->len = len;
 338
 339                 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
 340         }
 341
 342         if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
 343                 rc = -EPROTO;
 344                 goto err;
 345         }
 346
 347         kfree(data);
 348         fdput(f);
 349
 350         return 0;
 351
 352 err:
 353         kfree(data);
 354
 355         /* any failure in loading/parsing invalidates the entire list */
 356         {
 357                 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
 358
 359                 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
 360                         list_del(&trd->node);
 361                         kfree(trd);
 362                 }
 363         }
 364
 365         /* disallow further attempts after reading a corrupt/invalid file */
 366         deny_reading_verity_digests = true;
 367
 368         fdput(f);
 369
 370         return rc;
 371 }
 372
 373 /******************************** securityfs ********************************/
 374
 375 static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 376 {
 377         void __user *uarg = (void __user *)arg;
 378         unsigned int fd;
 379
 380         switch (cmd) {
 381         case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
 382                 if (copy_from_user(&fd, uarg, sizeof(fd)))
 383                         return -EFAULT;
 384
 385                 return read_trusted_verity_root_digests(fd);
 386
 387         default:
 388                 return -EINVAL;
 389         }
 390 }
 391
 392 static const struct file_operations loadpin_dm_verity_ops = {
 393         .unlocked_ioctl = dm_verity_ioctl,
 394         .compat_ioctl = compat_ptr_ioctl,
 395 };
 396
 397 /**
 398  * init_loadpin_securityfs - create the securityfs directory for LoadPin
 399  *
 400  * We can not put this method normally under the loadpin_init() code path since
 401  * the security subsystem gets initialized before the vfs caches.
 402  *
 403  * Returns 0 if the securityfs directory creation was successful.
 404  */
 405 static int __init init_loadpin_securityfs(void)
 406 {
 407         struct dentry *loadpin_dir, *dentry;
 408
 409         loadpin_dir = securityfs_create_dir("loadpin", NULL);
 410         if (IS_ERR(loadpin_dir)) {
 411                 pr_err("LoadPin: could not create securityfs dir: %ld\n",
 412                        PTR_ERR(loadpin_dir));
 413                 return PTR_ERR(loadpin_dir);
 414         }
 415
 416         dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
 417                                         (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
 418         if (IS_ERR(dentry)) {
 419                 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
 420                        PTR_ERR(dentry));
 421                 return PTR_ERR(dentry);
 422         }
 423
 424         return 0;
 425 }
 426
 427 fs_initcall(init_loadpin_securityfs);
 428
 429 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */
 430
 431 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
 432 module_param(enforce, int, 0);
 433 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
 434 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
 435 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");