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/module.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         case FILE_CHECK:
 118         case POST_SETATTR:
 119                 iint->ima_file_status = status;
 120                 break;
 121         case MODULE_CHECK ... MAX_CHECK - 1:
 122         default:
 123                 iint->ima_read_status = status;
 124                 break;
 125         }
 126 }
 127
 128 static void ima_cache_flags(struct integrity_iint_cache *iint,
 129                              enum ima_hooks func)
 130 {
 131         switch (func) {
 132         case MMAP_CHECK:
 133                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 134                 break;
 135         case BPRM_CHECK:
 136                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 137                 break;
 138         case CREDS_CHECK:
 139                 iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
 140                 break;
 141         case FILE_CHECK:
 142         case POST_SETATTR:
 143                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 144                 break;
 145         case MODULE_CHECK ... MAX_CHECK - 1:
 146         default:
 147                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 148                 break;
 149         }
 150 }
 151
 152 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 153                                  int xattr_len)
 154 {
 155         struct signature_v2_hdr *sig;
 156         enum hash_algo ret;
 157
 158         if (!xattr_value || xattr_len < 2)
 159                 /* return default hash algo */
 160                 return ima_hash_algo;
 161
 162         switch (xattr_value->type) {
 163         case EVM_IMA_XATTR_DIGSIG:
 164                 sig = (typeof(sig))xattr_value;
 165                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 166                         return ima_hash_algo;
 167                 return sig->hash_algo;
 168                 break;
 169         case IMA_XATTR_DIGEST_NG:
 170                 ret = xattr_value->digest[0];
 171                 if (ret < HASH_ALGO__LAST)
 172                         return ret;
 173                 break;
 174         case IMA_XATTR_DIGEST:
 175                 /* this is for backward compatibility */
 176                 if (xattr_len == 21) {
 177                         unsigned int zero = 0;
 178                         if (!memcmp(&xattr_value->digest[16], &zero, 4))
 179                                 return HASH_ALGO_MD5;
 180                         else
 181                                 return HASH_ALGO_SHA1;
 182                 } else if (xattr_len == 17)
 183                         return HASH_ALGO_MD5;
 184                 break;
 185         }
 186
 187         /* return default hash algo */
 188         return ima_hash_algo;
 189 }
 190
 191 int ima_read_xattr(struct dentry *dentry,
 192                    struct evm_ima_xattr_data **xattr_value)
 193 {
 194         ssize_t ret;
 195
 196         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 197                                  0, GFP_NOFS);
 198         if (ret == -EOPNOTSUPP)
 199                 ret = 0;
 200         return ret;
 201 }
 202
 203 /*
 204  * ima_appraise_measurement - appraise file measurement
 205  *
 206  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 207  * Assuming success, compare the xattr hash with the collected measurement.
 208  *
 209  * Return 0 on success, error code otherwise
 210  */
 211 int ima_appraise_measurement(enum ima_hooks func,
 212                              struct integrity_iint_cache *iint,
 213                              struct file *file, const unsigned char *filename,
 214                              struct evm_ima_xattr_data *xattr_value,
 215                              int xattr_len)
 216 {
 217         static const char op[] = "appraise_data";
 218         const char *cause = "unknown";
 219         struct dentry *dentry = file_dentry(file);
 220         struct inode *inode = d_backing_inode(dentry);
 221         enum integrity_status status = INTEGRITY_UNKNOWN;
 222         int rc = xattr_len, hash_start = 0;
 223
 224         if (!(inode->i_opflags & IOP_XATTR))
 225                 return INTEGRITY_UNKNOWN;
 226
 227         if (rc <= 0) {
 228                 if (rc && rc != -ENODATA)
 229                         goto out;
 230
 231                 cause = iint->flags & IMA_DIGSIG_REQUIRED ?
 232                                 "IMA-signature-required" : "missing-hash";
 233                 status = INTEGRITY_NOLABEL;
 234                 if (file->f_mode & FMODE_CREATED)
 235                         iint->flags |= IMA_NEW_FILE;
 236                 if ((iint->flags & IMA_NEW_FILE) &&
 237                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 238                      (inode->i_size == 0)))
 239                         status = INTEGRITY_PASS;
 240                 goto out;
 241         }
 242
 243         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 244         switch (status) {
 245         case INTEGRITY_PASS:
 246         case INTEGRITY_PASS_IMMUTABLE:
 247         case INTEGRITY_UNKNOWN:
 248                 break;
 249         case INTEGRITY_NOXATTRS:        /* No EVM protected xattrs. */
 250         case INTEGRITY_NOLABEL:         /* No security.evm xattr. */
 251                 cause = "missing-HMAC";
 252                 goto out;
 253         case INTEGRITY_FAIL:            /* Invalid HMAC/signature. */
 254                 cause = "invalid-HMAC";
 255                 goto out;
 256         default:
 257                 WARN_ONCE(true, "Unexpected integrity status %d\n", status);
 258         }
 259
 260         switch (xattr_value->type) {
 261         case IMA_XATTR_DIGEST_NG:
 262                 /* first byte contains algorithm id */
 263                 hash_start = 1;
 264                 /* fall through */
 265         case IMA_XATTR_DIGEST:
 266                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 267                         cause = "IMA-signature-required";
 268                         status = INTEGRITY_FAIL;
 269                         break;
 270                 }
 271                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 272                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 273                                 iint->ima_hash->length)
 274                         /* xattr length may be longer. md5 hash in previous
 275                            version occupied 20 bytes in xattr, instead of 16
 276                          */
 277                         rc = memcmp(&xattr_value->digest[hash_start],
 278                                     iint->ima_hash->digest,
 279                                     iint->ima_hash->length);
 280                 else
 281                         rc = -EINVAL;
 282                 if (rc) {
 283                         cause = "invalid-hash";
 284                         status = INTEGRITY_FAIL;
 285                         break;
 286                 }
 287                 status = INTEGRITY_PASS;
 288                 break;
 289         case EVM_IMA_XATTR_DIGSIG:
 290                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 291                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 292                                              (const char *)xattr_value, rc,
 293                                              iint->ima_hash->digest,
 294                                              iint->ima_hash->length);
 295                 if (rc == -EOPNOTSUPP) {
 296                         status = INTEGRITY_UNKNOWN;
 297                 } else if (rc) {
 298                         cause = "invalid-signature";
 299                         status = INTEGRITY_FAIL;
 300                 } else {
 301                         status = INTEGRITY_PASS;
 302                 }
 303                 break;
 304         default:
 305                 status = INTEGRITY_UNKNOWN;
 306                 cause = "unknown-ima-data";
 307                 break;
 308         }
 309
 310 out:
 311         /*
 312          * File signatures on some filesystems can not be properly verified.
 313          * When such filesystems are mounted by an untrusted mounter or on a
 314          * system not willing to accept such a risk, fail the file signature
 315          * verification.
 316          */
 317         if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
 318             ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
 319              (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 320                 status = INTEGRITY_FAIL;
 321                 cause = "unverifiable-signature";
 322                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 323                                     op, cause, rc, 0);
 324         } else if (status != INTEGRITY_PASS) {
 325                 /* Fix mode, but don't replace file signatures. */
 326                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 327                     (!xattr_value ||
 328                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 329                         if (!ima_fix_xattr(dentry, iint))
 330                                 status = INTEGRITY_PASS;
 331                 }
 332
 333                 /* Permit new files with file signatures, but without data. */
 334                 if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
 335                     xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
 336                         status = INTEGRITY_PASS;
 337                 }
 338
 339                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 340                                     op, cause, rc, 0);
 341         } else {
 342                 ima_cache_flags(iint, func);
 343         }
 344
 345         ima_set_cache_status(iint, func, status);
 346         return status;
 347 }
 348
 349 /*
 350  * ima_update_xattr - update 'security.ima' hash value
 351  */
 352 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 353 {
 354         struct dentry *dentry = file_dentry(file);
 355         int rc = 0;
 356
 357         /* do not collect and update hash for digital signatures */
 358         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 359                 return;
 360
 361         if ((iint->ima_file_status != INTEGRITY_PASS) &&
 362             !(iint->flags & IMA_HASH))
 363                 return;
 364
 365         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
 366         if (rc < 0)
 367                 return;
 368
 369         inode_lock(file_inode(file));
 370         ima_fix_xattr(dentry, iint);
 371         inode_unlock(file_inode(file));
 372 }
 373
 374 /**
 375  * ima_inode_post_setattr - reflect file metadata changes
 376  * @dentry: pointer to the affected dentry
 377  *
 378  * Changes to a dentry's metadata might result in needing to appraise.
 379  *
 380  * This function is called from notify_change(), which expects the caller
 381  * to lock the inode's i_mutex.
 382  */
 383 void ima_inode_post_setattr(struct dentry *dentry)
 384 {
 385         struct inode *inode = d_backing_inode(dentry);
 386         struct integrity_iint_cache *iint;
 387         int action;
 388
 389         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 390             || !(inode->i_opflags & IOP_XATTR))
 391                 return;
 392
 393         action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 394         if (!action)
 395                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 396         iint = integrity_iint_find(inode);
 397         if (iint) {
 398                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 399                 if (!action)
 400                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 401         }
 402 }
 403
 404 /*
 405  * ima_protect_xattr - protect 'security.ima'
 406  *
 407  * Ensure that not just anyone can modify or remove 'security.ima'.
 408  */
 409 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 410                              const void *xattr_value, size_t xattr_value_len)
 411 {
 412         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 413                 if (!capable(CAP_SYS_ADMIN))
 414                         return -EPERM;
 415                 return 1;
 416         }
 417         return 0;
 418 }
 419
 420 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 421 {
 422         struct integrity_iint_cache *iint;
 423
 424         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 425                 return;
 426
 427         iint = integrity_iint_find(inode);
 428         if (!iint)
 429                 return;
 430         iint->measured_pcrs = 0;
 431         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 432         if (digsig)
 433                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 434         else
 435                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 436 }
 437
 438 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 439                        const void *xattr_value, size_t xattr_value_len)
 440 {
 441         const struct evm_ima_xattr_data *xvalue = xattr_value;
 442         int result;
 443
 444         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 445                                    xattr_value_len);
 446         if (result == 1) {
 447                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 448                         return -EINVAL;
 449                 ima_reset_appraise_flags(d_backing_inode(dentry),
 450                         xvalue->type == EVM_IMA_XATTR_DIGSIG);
 451                 result = 0;
 452         }
 453         return result;
 454 }
 455
 456 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 457 {
 458         int result;
 459
 460         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 461         if (result == 1) {
 462                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 463                 result = 0;
 464         }
 465         return result;
 466 }