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                         status = INTEGRITY_PASS;
 210                 }
 211                 goto out;
 212         }
 213
 214         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 215         if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
 216                 if ((status == INTEGRITY_NOLABEL)
 217                     || (status == INTEGRITY_NOXATTRS))
 218                         cause = "missing-HMAC";
 219                 else if (status == INTEGRITY_FAIL)
 220                         cause = "invalid-HMAC";
 221                 goto out;
 222         }
 223         switch (xattr_value->type) {
 224         case IMA_XATTR_DIGEST_NG:
 225                 /* first byte contains algorithm id */
 226                 hash_start = 1;
 227         case IMA_XATTR_DIGEST:
 228                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 229                         cause = "IMA-signature-required";
 230                         status = INTEGRITY_FAIL;
 231                         break;
 232                 }
 233                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 234                                 iint->ima_hash->length)
 235                         /* xattr length may be longer. md5 hash in previous
 236                            version occupied 20 bytes in xattr, instead of 16
 237                          */
 238                         rc = memcmp(&xattr_value->digest[hash_start],
 239                                     iint->ima_hash->digest,
 240                                     iint->ima_hash->length);
 241                 else
 242                         rc = -EINVAL;
 243                 if (rc) {
 244                         cause = "invalid-hash";
 245                         status = INTEGRITY_FAIL;
 246                         break;
 247                 }
 248                 status = INTEGRITY_PASS;
 249                 break;
 250         case EVM_IMA_XATTR_DIGSIG:
 251                 iint->flags |= IMA_DIGSIG;
 252                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 253                                              (const char *)xattr_value, rc,
 254                                              iint->ima_hash->digest,
 255                                              iint->ima_hash->length);
 256                 if (rc == -EOPNOTSUPP) {
 257                         status = INTEGRITY_UNKNOWN;
 258                 } else if (rc) {
 259                         cause = "invalid-signature";
 260                         status = INTEGRITY_FAIL;
 261                 } else {
 262                         status = INTEGRITY_PASS;
 263                 }
 264                 break;
 265         default:
 266                 status = INTEGRITY_UNKNOWN;
 267                 cause = "unknown-ima-data";
 268                 break;
 269         }
 270
 271 out:
 272         if (status != INTEGRITY_PASS) {
 273                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 274                     (!xattr_value ||
 275                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 276                         if (!ima_fix_xattr(dentry, iint))
 277                                 status = INTEGRITY_PASS;
 278                 } else if ((inode->i_size == 0) &&
 279                            (iint->flags & IMA_NEW_FILE) &&
 280                            (xattr_value &&
 281                             xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
 282                         status = INTEGRITY_PASS;
 283                 }
 284                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 285                                     op, cause, rc, 0);
 286         } else {
 287                 ima_cache_flags(iint, func);
 288         }
 289         ima_set_cache_status(iint, func, status);
 290         return status;
 291 }
 292
 293 /*
 294  * ima_update_xattr - update 'security.ima' hash value
 295  */
 296 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 297 {
 298         struct dentry *dentry = file_dentry(file);
 299         int rc = 0;
 300
 301         /* do not collect and update hash for digital signatures */
 302         if (iint->flags & IMA_DIGSIG)
 303                 return;
 304
 305         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
 306         if (rc < 0)
 307                 return;
 308
 309         ima_fix_xattr(dentry, iint);
 310 }
 311
 312 /**
 313  * ima_inode_post_setattr - reflect file metadata changes
 314  * @dentry: pointer to the affected dentry
 315  *
 316  * Changes to a dentry's metadata might result in needing to appraise.
 317  *
 318  * This function is called from notify_change(), which expects the caller
 319  * to lock the inode's i_mutex.
 320  */
 321 void ima_inode_post_setattr(struct dentry *dentry)
 322 {
 323         struct inode *inode = d_backing_inode(dentry);
 324         struct integrity_iint_cache *iint;
 325         int must_appraise;
 326
 327         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 328             || !(inode->i_opflags & IOP_XATTR))
 329                 return;
 330
 331         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 332         iint = integrity_iint_find(inode);
 333         if (iint) {
 334                 iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
 335                                  IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
 336                                  IMA_ACTION_RULE_FLAGS);
 337                 if (must_appraise)
 338                         iint->flags |= IMA_APPRAISE;
 339         }
 340         if (!must_appraise)
 341                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 342 }
 343
 344 /*
 345  * ima_protect_xattr - protect 'security.ima'
 346  *
 347  * Ensure that not just anyone can modify or remove 'security.ima'.
 348  */
 349 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 350                              const void *xattr_value, size_t xattr_value_len)
 351 {
 352         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 353                 if (!capable(CAP_SYS_ADMIN))
 354                         return -EPERM;
 355                 return 1;
 356         }
 357         return 0;
 358 }
 359
 360 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 361 {
 362         struct integrity_iint_cache *iint;
 363
 364         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 365                 return;
 366
 367         iint = integrity_iint_find(inode);
 368         if (!iint)
 369                 return;
 370
 371         iint->flags &= ~IMA_DONE_MASK;
 372         iint->measured_pcrs = 0;
 373         if (digsig)
 374                 iint->flags |= IMA_DIGSIG;
 375         return;
 376 }
 377
 378 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 379                        const void *xattr_value, size_t xattr_value_len)
 380 {
 381         const struct evm_ima_xattr_data *xvalue = xattr_value;
 382         int result;
 383
 384         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 385                                    xattr_value_len);
 386         if (result == 1) {
 387                 bool digsig;
 388
 389                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 390                         return -EINVAL;
 391                 digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG);
 392                 if (!digsig && (ima_appraise & IMA_APPRAISE_ENFORCE))
 393                         return -EPERM;
 394                 ima_reset_appraise_flags(d_backing_inode(dentry), digsig);
 395                 result = 0;
 396         }
 397         return result;
 398 }
 399
 400 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 401 {
 402         int result;
 403
 404         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 405         if (result == 1) {
 406                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 407                 result = 0;
 408         }
 409         return result;
 410 }