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 #include <crypto/hash_info.h>
  19
  20 #include "ima.h"
  21
  22 static int __init default_appraise_setup(char *str)
  23 {
  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         return 1;
  31 }
  32
  33 __setup("ima_appraise=", default_appraise_setup);
  34
  35 /*
  36  * ima_must_appraise - set appraise flag
  37  *
  38  * Return 1 to appraise
  39  */
  40 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
  41 {
  42         if (!ima_appraise)
  43                 return 0;
  44
  45         return ima_match_policy(inode, func, mask, IMA_APPRAISE);
  46 }
  47
  48 static int ima_fix_xattr(struct dentry *dentry,
  49                          struct integrity_iint_cache *iint)
  50 {
  51         int rc, offset;
  52         u8 algo = iint->ima_hash->algo;
  53
  54         if (algo <= HASH_ALGO_SHA1) {
  55                 offset = 1;
  56                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  57         } else {
  58                 offset = 0;
  59                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  60                 iint->ima_hash->xattr.ng.algo = algo;
  61         }
  62         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  63                                    &iint->ima_hash->xattr.data[offset],
  64                                    (sizeof(iint->ima_hash->xattr) - offset) +
  65                                    iint->ima_hash->length, 0);
  66         return rc;
  67 }
  68
  69 /* Return specific func appraised cached result */
  70 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
  71                                            int func)
  72 {
  73         switch (func) {
  74         case MMAP_CHECK:
  75                 return iint->ima_mmap_status;
  76         case BPRM_CHECK:
  77                 return iint->ima_bprm_status;
  78         case MODULE_CHECK:
  79                 return iint->ima_module_status;
  80         case FIRMWARE_CHECK:
  81                 return iint->ima_firmware_status;
  82         case FILE_CHECK:
  83         default:
  84                 return iint->ima_file_status;
  85         }
  86 }
  87
  88 static void ima_set_cache_status(struct integrity_iint_cache *iint,
  89                                  int func, enum integrity_status status)
  90 {
  91         switch (func) {
  92         case MMAP_CHECK:
  93                 iint->ima_mmap_status = status;
  94                 break;
  95         case BPRM_CHECK:
  96                 iint->ima_bprm_status = status;
  97                 break;
  98         case MODULE_CHECK:
  99                 iint->ima_module_status = status;
 100                 break;
 101         case FIRMWARE_CHECK:
 102                 iint->ima_firmware_status = status;
 103                 break;
 104         case FILE_CHECK:
 105         default:
 106                 iint->ima_file_status = status;
 107                 break;
 108         }
 109 }
 110
 111 static void ima_cache_flags(struct integrity_iint_cache *iint, int func)
 112 {
 113         switch (func) {
 114         case MMAP_CHECK:
 115                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 116                 break;
 117         case BPRM_CHECK:
 118                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 119                 break;
 120         case MODULE_CHECK:
 121                 iint->flags |= (IMA_MODULE_APPRAISED | IMA_APPRAISED);
 122                 break;
 123         case FIRMWARE_CHECK:
 124                 iint->flags |= (IMA_FIRMWARE_APPRAISED | IMA_APPRAISED);
 125                 break;
 126         case FILE_CHECK:
 127         default:
 128                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 129                 break;
 130         }
 131 }
 132
 133 void ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value, int xattr_len,
 134                        struct ima_digest_data *hash)
 135 {
 136         struct signature_v2_hdr *sig;
 137
 138         if (!xattr_value || xattr_len < 2)
 139                 return;
 140
 141         switch (xattr_value->type) {
 142         case EVM_IMA_XATTR_DIGSIG:
 143                 sig = (typeof(sig))xattr_value;
 144                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 145                         return;
 146                 hash->algo = sig->hash_algo;
 147                 break;
 148         case IMA_XATTR_DIGEST_NG:
 149                 hash->algo = xattr_value->digest[0];
 150                 break;
 151         case IMA_XATTR_DIGEST:
 152                 /* this is for backward compatibility */
 153                 if (xattr_len == 21) {
 154                         unsigned int zero = 0;
 155                         if (!memcmp(&xattr_value->digest[16], &zero, 4))
 156                                 hash->algo = HASH_ALGO_MD5;
 157                         else
 158                                 hash->algo = HASH_ALGO_SHA1;
 159                 } else if (xattr_len == 17)
 160                         hash->algo = HASH_ALGO_MD5;
 161                 break;
 162         }
 163 }
 164
 165 int ima_read_xattr(struct dentry *dentry,
 166                    struct evm_ima_xattr_data **xattr_value)
 167 {
 168         struct inode *inode = d_backing_inode(dentry);
 169
 170         if (!inode->i_op->getxattr)
 171                 return 0;
 172
 173         return vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 174                                   0, GFP_NOFS);
 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(int func, struct integrity_iint_cache *iint,
 186                              struct file *file, const unsigned char *filename,
 187                              struct evm_ima_xattr_data *xattr_value,
 188                              int xattr_len, int opened)
 189 {
 190         static const char op[] = "appraise_data";
 191         char *cause = "unknown";
 192         struct dentry *dentry = file_dentry(file);
 193         struct inode *inode = d_backing_inode(dentry);
 194         enum integrity_status status = INTEGRITY_UNKNOWN;
 195         int rc = xattr_len, hash_start = 0;
 196
 197         if (!inode->i_op->getxattr)
 198                 return INTEGRITY_UNKNOWN;
 199
 200         if (rc <= 0) {
 201                 if (rc && rc != -ENODATA)
 202                         goto out;
 203
 204                 cause = "missing-hash";
 205                 status = INTEGRITY_NOLABEL;
 206                 if (opened & FILE_CREATED)
 207                         iint->flags |= IMA_NEW_FILE;
 208                 if ((iint->flags & IMA_NEW_FILE) &&
 209                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 210                      (inode->i_size == 0)))
 211                         status = INTEGRITY_PASS;
 212                 goto out;
 213         }
 214
 215         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 216         if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
 217                 if ((status == INTEGRITY_NOLABEL)
 218                     || (status == INTEGRITY_NOXATTRS))
 219                         cause = "missing-HMAC";
 220                 else if (status == INTEGRITY_FAIL)
 221                         cause = "invalid-HMAC";
 222                 goto out;
 223         }
 224         switch (xattr_value->type) {
 225         case IMA_XATTR_DIGEST_NG:
 226                 /* first byte contains algorithm id */
 227                 hash_start = 1;
 228         case IMA_XATTR_DIGEST:
 229                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 230                         cause = "IMA-signature-required";
 231                         status = INTEGRITY_FAIL;
 232                         break;
 233                 }
 234                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 235                                 iint->ima_hash->length)
 236                         /* xattr length may be longer. md5 hash in previous
 237                            version occupied 20 bytes in xattr, instead of 16
 238                          */
 239                         rc = memcmp(&xattr_value->digest[hash_start],
 240                                     iint->ima_hash->digest,
 241                                     iint->ima_hash->length);
 242                 else
 243                         rc = -EINVAL;
 244                 if (rc) {
 245                         cause = "invalid-hash";
 246                         status = INTEGRITY_FAIL;
 247                         break;
 248                 }
 249                 status = INTEGRITY_PASS;
 250                 break;
 251         case EVM_IMA_XATTR_DIGSIG:
 252                 iint->flags |= IMA_DIGSIG;
 253                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 254                                              (const char *)xattr_value, rc,
 255                                              iint->ima_hash->digest,
 256                                              iint->ima_hash->length);
 257                 if (rc == -EOPNOTSUPP) {
 258                         status = INTEGRITY_UNKNOWN;
 259                 } else if (rc) {
 260                         cause = "invalid-signature";
 261                         status = INTEGRITY_FAIL;
 262                 } else {
 263                         status = INTEGRITY_PASS;
 264                 }
 265                 break;
 266         default:
 267                 status = INTEGRITY_UNKNOWN;
 268                 cause = "unknown-ima-data";
 269                 break;
 270         }
 271
 272 out:
 273         if (status != INTEGRITY_PASS) {
 274                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 275                     (!xattr_value ||
 276                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 277                         if (!ima_fix_xattr(dentry, iint))
 278                                 status = INTEGRITY_PASS;
 279                 }
 280                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 281                                     op, cause, rc, 0);
 282         } else {
 283                 ima_cache_flags(iint, func);
 284         }
 285         ima_set_cache_status(iint, func, status);
 286         return status;
 287 }
 288
 289 /*
 290  * ima_update_xattr - update 'security.ima' hash value
 291  */
 292 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 293 {
 294         struct dentry *dentry = file_dentry(file);
 295         int rc = 0;
 296
 297         /* do not collect and update hash for digital signatures */
 298         if (iint->flags & IMA_DIGSIG)
 299                 return;
 300
 301         if (iint->ima_file_status != INTEGRITY_PASS)
 302                 return;
 303
 304         rc = ima_collect_measurement(iint, file, NULL, NULL);
 305         if (rc < 0)
 306                 return;
 307
 308         ima_fix_xattr(dentry, iint);
 309 }
 310
 311 /**
 312  * ima_inode_post_setattr - reflect file metadata changes
 313  * @dentry: pointer to the affected dentry
 314  *
 315  * Changes to a dentry's metadata might result in needing to appraise.
 316  *
 317  * This function is called from notify_change(), which expects the caller
 318  * to lock the inode's i_mutex.
 319  */
 320 void ima_inode_post_setattr(struct dentry *dentry)
 321 {
 322         struct inode *inode = d_backing_inode(dentry);
 323         struct integrity_iint_cache *iint;
 324         int must_appraise, rc;
 325
 326         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 327             || !inode->i_op->removexattr)
 328                 return;
 329
 330         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 331         iint = integrity_iint_find(inode);
 332         if (iint) {
 333                 iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
 334                                  IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
 335                                  IMA_ACTION_FLAGS);
 336                 if (must_appraise)
 337                         iint->flags |= IMA_APPRAISE;
 338         }
 339         if (!must_appraise)
 340                 rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
 341         return;
 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         if (digsig)
 373                 iint->flags |= IMA_DIGSIG;
 374         return;
 375 }
 376
 377 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 378                        const void *xattr_value, size_t xattr_value_len)
 379 {
 380         const struct evm_ima_xattr_data *xvalue = xattr_value;
 381         int result;
 382
 383         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 384                                    xattr_value_len);
 385         if (result == 1) {
 386                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 387                         return -EINVAL;
 388                 ima_reset_appraise_flags(d_backing_inode(dentry),
 389                          (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0);
 390                 result = 0;
 391         }
 392         return result;
 393 }
 394
 395 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 396 {
 397         int result;
 398
 399         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 400         if (result == 1) {
 401                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 402                 result = 0;
 403         }
 404         return result;
 405 }