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         if (strncmp(str, "off", 3) == 0)
  24                 ima_appraise = 0;
  25         else if (strncmp(str, "log", 3) == 0)
  26                 ima_appraise = IMA_APPRAISE_LOG;
  27         else if (strncmp(str, "fix", 3) == 0)
  28                 ima_appraise = IMA_APPRAISE_FIX;
  29         return 1;
  30 }
  31
  32 __setup("ima_appraise=", default_appraise_setup);
  33
  34 /*
  35  * ima_must_appraise - set appraise flag
  36  *
  37  * Return 1 to appraise
  38  */
  39 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
  40 {
  41         if (!ima_appraise)
  42                 return 0;
  43
  44         return ima_match_policy(inode, func, mask, IMA_APPRAISE, NULL);
  45 }
  46
  47 static int ima_fix_xattr(struct dentry *dentry,
  48                          struct integrity_iint_cache *iint)
  49 {
  50         int rc, offset;
  51         u8 algo = iint->ima_hash->algo;
  52
  53         if (algo <= HASH_ALGO_SHA1) {
  54                 offset = 1;
  55                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  56         } else {
  57                 offset = 0;
  58                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  59                 iint->ima_hash->xattr.ng.algo = algo;
  60         }
  61         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  62                                    &iint->ima_hash->xattr.data[offset],
  63                                    (sizeof(iint->ima_hash->xattr) - offset) +
  64                                    iint->ima_hash->length, 0);
  65         return rc;
  66 }
  67
  68 /* Return specific func appraised cached result */
  69 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
  70                                            enum ima_hooks func)
  71 {
  72         switch (func) {
  73         case MMAP_CHECK:
  74                 return iint->ima_mmap_status;
  75         case BPRM_CHECK:
  76                 return iint->ima_bprm_status;
  77         case FILE_CHECK:
  78         case POST_SETATTR:
  79                 return iint->ima_file_status;
  80         case MODULE_CHECK ... MAX_CHECK - 1:
  81         default:
  82                 return iint->ima_read_status;
  83         }
  84 }
  85
  86 static void ima_set_cache_status(struct integrity_iint_cache *iint,
  87                                  enum ima_hooks func,
  88                                  enum integrity_status status)
  89 {
  90         switch (func) {
  91         case MMAP_CHECK:
  92                 iint->ima_mmap_status = status;
  93                 break;
  94         case BPRM_CHECK:
  95                 iint->ima_bprm_status = status;
  96                 break;
  97         case FILE_CHECK:
  98         case POST_SETATTR:
  99                 iint->ima_file_status = status;
 100                 break;
 101         case MODULE_CHECK ... MAX_CHECK - 1:
 102         default:
 103                 iint->ima_read_status = status;
 104                 break;
 105         }
 106 }
 107
 108 static void ima_cache_flags(struct integrity_iint_cache *iint,
 109                              enum ima_hooks func)
 110 {
 111         switch (func) {
 112         case MMAP_CHECK:
 113                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 114                 break;
 115         case BPRM_CHECK:
 116                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 117                 break;
 118         case FILE_CHECK:
 119         case POST_SETATTR:
 120                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 121                 break;
 122         case MODULE_CHECK ... MAX_CHECK - 1:
 123         default:
 124                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 125                 break;
 126         }
 127 }
 128
 129 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 130                                  int xattr_len)
 131 {
 132         struct signature_v2_hdr *sig;
 133
 134         if (!xattr_value || xattr_len < 2)
 135                 /* return default hash algo */
 136                 return ima_hash_algo;
 137
 138         switch (xattr_value->type) {
 139         case EVM_IMA_XATTR_DIGSIG:
 140                 sig = (typeof(sig))xattr_value;
 141                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 142                         return ima_hash_algo;
 143                 return sig->hash_algo;
 144                 break;
 145         case IMA_XATTR_DIGEST_NG:
 146                 return xattr_value->digest[0];
 147                 break;
 148         case IMA_XATTR_DIGEST:
 149                 /* this is for backward compatibility */
 150                 if (xattr_len == 21) {
 151                         unsigned int zero = 0;
 152                         if (!memcmp(&xattr_value->digest[16], &zero, 4))
 153                                 return HASH_ALGO_MD5;
 154                         else
 155                                 return HASH_ALGO_SHA1;
 156                 } else if (xattr_len == 17)
 157                         return HASH_ALGO_MD5;
 158                 break;
 159         }
 160
 161         /* return default hash algo */
 162         return ima_hash_algo;
 163 }
 164
 165 int ima_read_xattr(struct dentry *dentry,
 166                    struct evm_ima_xattr_data **xattr_value)
 167 {
 168         ssize_t ret;
 169
 170         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 171                                  0, GFP_NOFS);
 172         if (ret == -EOPNOTSUPP)
 173                 ret = 0;
 174         return ret;
 175 }
 176
 177 /*
 178  * ima_appraise_measurement - appraise file measurement
 179  *
 180  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 181  * Assuming success, compare the xattr hash with the collected measurement.
 182  *
 183  * Return 0 on success, error code otherwise
 184  */
 185 int ima_appraise_measurement(enum ima_hooks func,
 186                              struct integrity_iint_cache *iint,
 187                              struct file *file, const unsigned char *filename,
 188                              struct evm_ima_xattr_data *xattr_value,
 189                              int xattr_len, int opened)
 190 {
 191         static const char op[] = "appraise_data";
 192         char *cause = "unknown";
 193         struct dentry *dentry = file_dentry(file);
 194         struct inode *inode = d_backing_inode(dentry);
 195         enum integrity_status status = INTEGRITY_UNKNOWN;
 196         int rc = xattr_len, hash_start = 0;
 197
 198         if (!(inode->i_opflags & IOP_XATTR))
 199                 return INTEGRITY_UNKNOWN;
 200
 201         if (rc <= 0) {
 202                 if (rc && rc != -ENODATA)
 203                         goto out;
 204
 205                 cause = "missing-hash";
 206                 status = INTEGRITY_NOLABEL;
 207                 if (opened & FILE_CREATED)
 208                         iint->flags |= IMA_NEW_FILE;
 209                 if ((iint->flags & IMA_NEW_FILE) &&
 210                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 211                      (inode->i_size == 0)))
 212                         status = INTEGRITY_PASS;
 213                 goto out;
 214         }
 215
 216         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 217         if ((status != INTEGRITY_PASS) &&
 218             (status != INTEGRITY_PASS_IMMUTABLE) &&
 219             (status != INTEGRITY_UNKNOWN)) {
 220                 if ((status == INTEGRITY_NOLABEL)
 221                     || (status == INTEGRITY_NOXATTRS))
 222                         cause = "missing-HMAC";
 223                 else if (status == INTEGRITY_FAIL)
 224                         cause = "invalid-HMAC";
 225                 goto out;
 226         }
 227         switch (xattr_value->type) {
 228         case IMA_XATTR_DIGEST_NG:
 229                 /* first byte contains algorithm id */
 230                 hash_start = 1;
 231         case IMA_XATTR_DIGEST:
 232                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 233                         cause = "IMA-signature-required";
 234                         status = INTEGRITY_FAIL;
 235                         break;
 236                 }
 237                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 238                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 239                                 iint->ima_hash->length)
 240                         /* xattr length may be longer. md5 hash in previous
 241                            version occupied 20 bytes in xattr, instead of 16
 242                          */
 243                         rc = memcmp(&xattr_value->digest[hash_start],
 244                                     iint->ima_hash->digest,
 245                                     iint->ima_hash->length);
 246                 else
 247                         rc = -EINVAL;
 248                 if (rc) {
 249                         cause = "invalid-hash";
 250                         status = INTEGRITY_FAIL;
 251                         break;
 252                 }
 253                 status = INTEGRITY_PASS;
 254                 break;
 255         case EVM_IMA_XATTR_DIGSIG:
 256                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 257                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 258                                              (const char *)xattr_value, rc,
 259                                              iint->ima_hash->digest,
 260                                              iint->ima_hash->length);
 261                 if (rc == -EOPNOTSUPP) {
 262                         status = INTEGRITY_UNKNOWN;
 263                 } else if (rc) {
 264                         cause = "invalid-signature";
 265                         status = INTEGRITY_FAIL;
 266                 } else {
 267                         status = INTEGRITY_PASS;
 268                 }
 269                 break;
 270         default:
 271                 status = INTEGRITY_UNKNOWN;
 272                 cause = "unknown-ima-data";
 273                 break;
 274         }
 275
 276 out:
 277         if (status != INTEGRITY_PASS) {
 278                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 279                     (!xattr_value ||
 280                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 281                         if (!ima_fix_xattr(dentry, iint))
 282                                 status = INTEGRITY_PASS;
 283                 } else if ((inode->i_size == 0) &&
 284                            (iint->flags & IMA_NEW_FILE) &&
 285                            (xattr_value &&
 286                             xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
 287                         status = INTEGRITY_PASS;
 288                 }
 289                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 290                                     op, cause, rc, 0);
 291         } else {
 292                 ima_cache_flags(iint, func);
 293         }
 294         ima_set_cache_status(iint, func, status);
 295         return status;
 296 }
 297
 298 /*
 299  * ima_update_xattr - update 'security.ima' hash value
 300  */
 301 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 302 {
 303         struct dentry *dentry = file_dentry(file);
 304         int rc = 0;
 305
 306         /* do not collect and update hash for digital signatures */
 307         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 308                 return;
 309
 310         if (iint->ima_file_status != INTEGRITY_PASS)
 311                 return;
 312
 313         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
 314         if (rc < 0)
 315                 return;
 316
 317         inode_lock(file_inode(file));
 318         ima_fix_xattr(dentry, iint);
 319         inode_unlock(file_inode(file));
 320 }
 321
 322 /**
 323  * ima_inode_post_setattr - reflect file metadata changes
 324  * @dentry: pointer to the affected dentry
 325  *
 326  * Changes to a dentry's metadata might result in needing to appraise.
 327  *
 328  * This function is called from notify_change(), which expects the caller
 329  * to lock the inode's i_mutex.
 330  */
 331 void ima_inode_post_setattr(struct dentry *dentry)
 332 {
 333         struct inode *inode = d_backing_inode(dentry);
 334         struct integrity_iint_cache *iint;
 335         int must_appraise;
 336
 337         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 338             || !(inode->i_opflags & IOP_XATTR))
 339                 return;
 340
 341         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 342         if (!must_appraise)
 343                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 344         iint = integrity_iint_find(inode);
 345         if (iint) {
 346                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 347                 if (!must_appraise)
 348                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 349         }
 350 }
 351
 352 /*
 353  * ima_protect_xattr - protect 'security.ima'
 354  *
 355  * Ensure that not just anyone can modify or remove 'security.ima'.
 356  */
 357 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 358                              const void *xattr_value, size_t xattr_value_len)
 359 {
 360         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 361                 if (!capable(CAP_SYS_ADMIN))
 362                         return -EPERM;
 363                 return 1;
 364         }
 365         return 0;
 366 }
 367
 368 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 369 {
 370         struct integrity_iint_cache *iint;
 371
 372         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 373                 return;
 374
 375         iint = integrity_iint_find(inode);
 376         if (!iint)
 377                 return;
 378         iint->measured_pcrs = 0;
 379         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 380         if (digsig)
 381                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 382         else
 383                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 384 }
 385
 386 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 387                        const void *xattr_value, size_t xattr_value_len)
 388 {
 389         const struct evm_ima_xattr_data *xvalue = xattr_value;
 390         int result;
 391
 392         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 393                                    xattr_value_len);
 394         if (result == 1) {
 395                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 396                         return -EINVAL;
 397                 ima_reset_appraise_flags(d_backing_inode(dentry),
 398                          (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0);
 399                 result = 0;
 400         }
 401         return result;
 402 }
 403
 404 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 405 {
 406         int result;
 407
 408         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 409         if (result == 1) {
 410                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 411                 result = 0;
 412         }
 413         return result;
 414 }