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