security/integrity/ima/ima_appraise.c

   1 /*
   2  * Copyright (C) 2011 IBM Corporation
   3  *
   4  * Author:
   5  * Mimi Zohar <zohar@us.ibm.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation, version 2 of the License.
  10  */
  11 #include <linux/init.h>
  12 #include <linux/file.h>
  13 #include <linux/fs.h>
  14 #include <linux/xattr.h>
  15 #include <linux/magic.h>
  16 #include <linux/ima.h>
  17 #include <linux/evm.h>
  18
  19 #include "ima.h"
  20
  21 static int __init default_appraise_setup(char *str)
  22 {
  23 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
  24         if (strncmp(str, "off", 3) == 0)
  25                 ima_appraise = 0;
  26         else if (strncmp(str, "log", 3) == 0)
  27                 ima_appraise = IMA_APPRAISE_LOG;
  28         else if (strncmp(str, "fix", 3) == 0)
  29                 ima_appraise = IMA_APPRAISE_FIX;
  30 #endif
  31         return 1;
  32 }
  33
  34 __setup("ima_appraise=", default_appraise_setup);
  35
  36 /*
  37  * is_ima_appraise_enabled - return appraise status
  38  *
  39  * Only return enabled, if not in ima_appraise="fix" or "log" modes.
  40  */
  41 bool is_ima_appraise_enabled(void)
  42 {
  43         return ima_appraise & IMA_APPRAISE_ENFORCE;
  44 }
  45
  46 /*
  47  * ima_must_appraise - set appraise flag
  48  *
  49  * Return 1 to appraise or hash
  50  */
  51 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
  52 {
  53         u32 secid;
  54
  55         if (!ima_appraise)
  56                 return 0;
  57
  58         security_task_getsecid(current, &secid);
  59         return ima_match_policy(inode, current_cred(), secid, func, mask,
  60                                 IMA_APPRAISE | IMA_HASH, NULL);
  61 }
  62
  63 static int ima_fix_xattr(struct dentry *dentry,
  64                          struct integrity_iint_cache *iint)
  65 {
  66         int rc, offset;
  67         u8 algo = iint->ima_hash->algo;
  68
  69         if (algo <= HASH_ALGO_SHA1) {
  70                 offset = 1;
  71                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  72         } else {
  73                 offset = 0;
  74                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  75                 iint->ima_hash->xattr.ng.algo = algo;
  76         }
  77         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  78                                    &iint->ima_hash->xattr.data[offset],
  79                                    (sizeof(iint->ima_hash->xattr) - offset) +
  80                                    iint->ima_hash->length, 0);
  81         return rc;
  82 }
  83
  84 /* Return specific func appraised cached result */
  85 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
  86                                            enum ima_hooks func)
  87 {
  88         switch (func) {
  89         case MMAP_CHECK:
  90                 return iint->ima_mmap_status;
  91         case BPRM_CHECK:
  92                 return iint->ima_bprm_status;
  93         case CREDS_CHECK:
  94                 return iint->ima_creds_status;
  95         case FILE_CHECK:
  96         case POST_SETATTR:
  97                 return iint->ima_file_status;
  98         case MODULE_CHECK ... MAX_CHECK - 1:
  99         default:
 100                 return iint->ima_read_status;
 101         }
 102 }
 103
 104 static void ima_set_cache_status(struct integrity_iint_cache *iint,
 105                                  enum ima_hooks func,
 106                                  enum integrity_status status)
 107 {
 108         switch (func) {
 109         case MMAP_CHECK:
 110                 iint->ima_mmap_status = status;
 111                 break;
 112         case BPRM_CHECK:
 113                 iint->ima_bprm_status = status;
 114                 break;
 115         case CREDS_CHECK:
 116                 iint->ima_creds_status = status;
 117                 break;
 118         case FILE_CHECK:
 119         case POST_SETATTR:
 120                 iint->ima_file_status = status;
 121                 break;
 122         case MODULE_CHECK ... MAX_CHECK - 1:
 123         default:
 124                 iint->ima_read_status = status;
 125                 break;
 126         }
 127 }
 128
 129 static void ima_cache_flags(struct integrity_iint_cache *iint,
 130                              enum ima_hooks func)
 131 {
 132         switch (func) {
 133         case MMAP_CHECK:
 134                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 135                 break;
 136         case BPRM_CHECK:
 137                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 138                 break;
 139         case CREDS_CHECK:
 140                 iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
 141                 break;
 142         case FILE_CHECK:
 143         case POST_SETATTR:
 144                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 145                 break;
 146         case MODULE_CHECK ... MAX_CHECK - 1:
 147         default:
 148                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 149                 break;
 150         }
 151 }
 152
 153 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 154                                  int xattr_len)
 155 {
 156         struct signature_v2_hdr *sig;
 157         enum hash_algo ret;
 158
 159         if (!xattr_value || xattr_len < 2)
 160                 /* return default hash algo */
 161                 return ima_hash_algo;
 162
 163         switch (xattr_value->type) {
 164         case EVM_IMA_XATTR_DIGSIG:
 165                 sig = (typeof(sig))xattr_value;
 166                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 167                         return ima_hash_algo;
 168                 return sig->hash_algo;
 169                 break;
 170         case IMA_XATTR_DIGEST_NG:
 171                 ret = xattr_value->digest[0];
 172                 if (ret < HASH_ALGO__LAST)
 173                         return ret;
 174                 break;
 175         case IMA_XATTR_DIGEST:
 176                 /* this is for backward compatibility */
 177                 if (xattr_len == 21) {
 178                         unsigned int zero = 0;
 179                         if (!memcmp(&xattr_value->digest[16], &zero, 4))
 180                                 return HASH_ALGO_MD5;
 181                         else
 182                                 return HASH_ALGO_SHA1;
 183                 } else if (xattr_len == 17)
 184                         return HASH_ALGO_MD5;
 185                 break;
 186         }
 187
 188         /* return default hash algo */
 189         return ima_hash_algo;
 190 }
 191
 192 int ima_read_xattr(struct dentry *dentry,
 193                    struct evm_ima_xattr_data **xattr_value)
 194 {
 195         ssize_t ret;
 196
 197         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 198                                  0, GFP_NOFS);
 199         if (ret == -EOPNOTSUPP)
 200                 ret = 0;
 201         return ret;
 202 }
 203
 204 /*
 205  * ima_appraise_measurement - appraise file measurement
 206  *
 207  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 208  * Assuming success, compare the xattr hash with the collected measurement.
 209  *
 210  * Return 0 on success, error code otherwise
 211  */
 212 int ima_appraise_measurement(enum ima_hooks func,
 213                              struct integrity_iint_cache *iint,
 214                              struct file *file, const unsigned char *filename,
 215                              struct evm_ima_xattr_data *xattr_value,
 216                              int xattr_len)
 217 {
 218         static const char op[] = "appraise_data";
 219         const char *cause = "unknown";
 220         struct dentry *dentry = file_dentry(file);
 221         struct inode *inode = d_backing_inode(dentry);
 222         enum integrity_status status = INTEGRITY_UNKNOWN;
 223         int rc = xattr_len, hash_start = 0;
 224
 225         if (!(inode->i_opflags & IOP_XATTR))
 226                 return INTEGRITY_UNKNOWN;
 227
 228         if (rc <= 0) {
 229                 if (rc && rc != -ENODATA)
 230                         goto out;
 231
 232                 cause = iint->flags & IMA_DIGSIG_REQUIRED ?
 233                                 "IMA-signature-required" : "missing-hash";
 234                 status = INTEGRITY_NOLABEL;
 235                 if (file->f_mode & FMODE_CREATED)
 236                         iint->flags |= IMA_NEW_FILE;
 237                 if ((iint->flags & IMA_NEW_FILE) &&
 238                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 239                      (inode->i_size == 0)))
 240                         status = INTEGRITY_PASS;
 241                 goto out;
 242         }
 243
 244         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 245         switch (status) {
 246         case INTEGRITY_PASS:
 247         case INTEGRITY_PASS_IMMUTABLE:
 248         case INTEGRITY_UNKNOWN:
 249                 break;
 250         case INTEGRITY_NOXATTRS:        /* No EVM protected xattrs. */
 251         case INTEGRITY_NOLABEL:         /* No security.evm xattr. */
 252                 cause = "missing-HMAC";
 253                 goto out;
 254         case INTEGRITY_FAIL:            /* Invalid HMAC/signature. */
 255                 cause = "invalid-HMAC";
 256                 goto out;
 257         default:
 258                 WARN_ONCE(true, "Unexpected integrity status %d\n", status);
 259         }
 260
 261         switch (xattr_value->type) {
 262         case IMA_XATTR_DIGEST_NG:
 263                 /* first byte contains algorithm id */
 264                 hash_start = 1;
 265                 /* fall through */
 266         case IMA_XATTR_DIGEST:
 267                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 268                         cause = "IMA-signature-required";
 269                         status = INTEGRITY_FAIL;
 270                         break;
 271                 }
 272                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 273                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 274                                 iint->ima_hash->length)
 275                         /* xattr length may be longer. md5 hash in previous
 276                            version occupied 20 bytes in xattr, instead of 16
 277                          */
 278                         rc = memcmp(&xattr_value->digest[hash_start],
 279                                     iint->ima_hash->digest,
 280                                     iint->ima_hash->length);
 281                 else
 282                         rc = -EINVAL;
 283                 if (rc) {
 284                         cause = "invalid-hash";
 285                         status = INTEGRITY_FAIL;
 286                         break;
 287                 }
 288                 status = INTEGRITY_PASS;
 289                 break;
 290         case EVM_IMA_XATTR_DIGSIG:
 291                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 292                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 293                                              (const char *)xattr_value,
 294                                              xattr_len,
 295                                              iint->ima_hash->digest,
 296                                              iint->ima_hash->length);
 297                 if (rc == -EOPNOTSUPP) {
 298                         status = INTEGRITY_UNKNOWN;
 299                         break;
 300                 }
 301                 if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 302                     func == KEXEC_KERNEL_CHECK)
 303                         rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
 304                                                      (const char *)xattr_value,
 305                                                      xattr_len,
 306                                                      iint->ima_hash->digest,
 307                                                      iint->ima_hash->length);
 308                 if (rc) {
 309                         cause = "invalid-signature";
 310                         status = INTEGRITY_FAIL;
 311                 } else {
 312                         status = INTEGRITY_PASS;
 313                 }
 314                 break;
 315         default:
 316                 status = INTEGRITY_UNKNOWN;
 317                 cause = "unknown-ima-data";
 318                 break;
 319         }
 320
 321 out:
 322         /*
 323          * File signatures on some filesystems can not be properly verified.
 324          * When such filesystems are mounted by an untrusted mounter or on a
 325          * system not willing to accept such a risk, fail the file signature
 326          * verification.
 327          */
 328         if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
 329             ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
 330              (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 331                 status = INTEGRITY_FAIL;
 332                 cause = "unverifiable-signature";
 333                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 334                                     op, cause, rc, 0);
 335         } else if (status != INTEGRITY_PASS) {
 336                 /* Fix mode, but don't replace file signatures. */
 337                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 338                     (!xattr_value ||
 339                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 340                         if (!ima_fix_xattr(dentry, iint))
 341                                 status = INTEGRITY_PASS;
 342                 }
 343
 344                 /* Permit new files with file signatures, but without data. */
 345                 if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
 346                     xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
 347                         status = INTEGRITY_PASS;
 348                 }
 349
 350                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 351                                     op, cause, rc, 0);
 352         } else {
 353                 ima_cache_flags(iint, func);
 354         }
 355
 356         ima_set_cache_status(iint, func, status);
 357         return status;
 358 }
 359
 360 /*
 361  * ima_update_xattr - update 'security.ima' hash value
 362  */
 363 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 364 {
 365         struct dentry *dentry = file_dentry(file);
 366         int rc = 0;
 367
 368         /* do not collect and update hash for digital signatures */
 369         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 370                 return;
 371
 372         if ((iint->ima_file_status != INTEGRITY_PASS) &&
 373             !(iint->flags & IMA_HASH))
 374                 return;
 375
 376         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
 377         if (rc < 0)
 378                 return;
 379
 380         inode_lock(file_inode(file));
 381         ima_fix_xattr(dentry, iint);
 382         inode_unlock(file_inode(file));
 383 }
 384
 385 /**
 386  * ima_inode_post_setattr - reflect file metadata changes
 387  * @dentry: pointer to the affected dentry
 388  *
 389  * Changes to a dentry's metadata might result in needing to appraise.
 390  *
 391  * This function is called from notify_change(), which expects the caller
 392  * to lock the inode's i_mutex.
 393  */
 394 void ima_inode_post_setattr(struct dentry *dentry)
 395 {
 396         struct inode *inode = d_backing_inode(dentry);
 397         struct integrity_iint_cache *iint;
 398         int action;
 399
 400         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 401             || !(inode->i_opflags & IOP_XATTR))
 402                 return;
 403
 404         action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 405         if (!action)
 406                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 407         iint = integrity_iint_find(inode);
 408         if (iint) {
 409                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 410                 if (!action)
 411                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 412         }
 413 }
 414
 415 /*
 416  * ima_protect_xattr - protect 'security.ima'
 417  *
 418  * Ensure that not just anyone can modify or remove 'security.ima'.
 419  */
 420 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 421                              const void *xattr_value, size_t xattr_value_len)
 422 {
 423         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 424                 if (!capable(CAP_SYS_ADMIN))
 425                         return -EPERM;
 426                 return 1;
 427         }
 428         return 0;
 429 }
 430
 431 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 432 {
 433         struct integrity_iint_cache *iint;
 434
 435         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 436                 return;
 437
 438         iint = integrity_iint_find(inode);
 439         if (!iint)
 440                 return;
 441         iint->measured_pcrs = 0;
 442         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 443         if (digsig)
 444                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 445         else
 446                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 447 }
 448
 449 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 450                        const void *xattr_value, size_t xattr_value_len)
 451 {
 452         const struct evm_ima_xattr_data *xvalue = xattr_value;
 453         int result;
 454
 455         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 456                                    xattr_value_len);
 457         if (result == 1) {
 458                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 459                         return -EINVAL;
 460                 ima_reset_appraise_flags(d_backing_inode(dentry),
 461                         xvalue->type == EVM_IMA_XATTR_DIGSIG);
 462                 result = 0;
 463         }
 464         return result;
 465 }
 466
 467 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 468 {
 469         int result;
 470
 471         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 472         if (result == 1) {
 473                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 474                 result = 0;
 475         }
 476         return result;
 477 }