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 FIRMWARE_CHECK:
  79                 return iint->ima_firmware_status;
  80         case FILE_CHECK:
  81         default:
  82                 return iint->ima_file_status;
  83         }
  84 }
  85
  86 static void ima_set_cache_status(struct integrity_iint_cache *iint,
  87                                  int func, enum integrity_status status)
  88 {
  89         switch (func) {
  90         case MMAP_CHECK:
  91                 iint->ima_mmap_status = status;
  92                 break;
  93         case BPRM_CHECK:
  94                 iint->ima_bprm_status = status;
  95                 break;
  96         case MODULE_CHECK:
  97                 iint->ima_module_status = status;
  98                 break;
  99         case FIRMWARE_CHECK:
 100                 iint->ima_firmware_status = status;
 101                 break;
 102         case FILE_CHECK:
 103         default:
 104                 iint->ima_file_status = status;
 105                 break;
 106         }
 107 }
 108
 109 static void ima_cache_flags(struct integrity_iint_cache *iint, int 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 MODULE_CHECK:
 119                 iint->flags |= (IMA_MODULE_APPRAISED | IMA_APPRAISED);
 120                 break;
 121         case FIRMWARE_CHECK:
 122                 iint->flags |= (IMA_FIRMWARE_APPRAISED | IMA_APPRAISED);
 123                 break;
 124         case FILE_CHECK:
 125         default:
 126                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 127                 break;
 128         }
 129 }
 130
 131 void ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value, int xattr_len,
 132                        struct ima_digest_data *hash)
 133 {
 134         struct signature_v2_hdr *sig;
 135
 136         if (!xattr_value || xattr_len < 2)
 137                 return;
 138
 139         switch (xattr_value->type) {
 140         case EVM_IMA_XATTR_DIGSIG:
 141                 sig = (typeof(sig))xattr_value;
 142                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 143                         return;
 144                 hash->algo = sig->hash_algo;
 145                 break;
 146         case IMA_XATTR_DIGEST_NG:
 147                 hash->algo = xattr_value->digest[0];
 148                 break;
 149         case IMA_XATTR_DIGEST:
 150                 /* this is for backward compatibility */
 151                 if (xattr_len == 21) {
 152                         unsigned int zero = 0;
 153                         if (!memcmp(&xattr_value->digest[16], &zero, 4))
 154                                 hash->algo = HASH_ALGO_MD5;
 155                         else
 156                                 hash->algo = HASH_ALGO_SHA1;
 157                 } else if (xattr_len == 17)
 158                         hash->algo = HASH_ALGO_MD5;
 159                 break;
 160         }
 161 }
 162
 163 int ima_read_xattr(struct dentry *dentry,
 164                    struct evm_ima_xattr_data **xattr_value)
 165 {
 166         struct inode *inode = dentry->d_inode;
 167
 168         if (!inode->i_op->getxattr)
 169                 return 0;
 170
 171         return vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 172                                   0, GFP_NOFS);
 173 }
 174
 175 /*
 176  * ima_appraise_measurement - appraise file measurement
 177  *
 178  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 179  * Assuming success, compare the xattr hash with the collected measurement.
 180  *
 181  * Return 0 on success, error code otherwise
 182  */
 183 int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
 184                              struct file *file, const unsigned char *filename,
 185                              struct evm_ima_xattr_data *xattr_value,
 186                              int xattr_len)
 187 {
 188         static const char op[] = "appraise_data";
 189         char *cause = "unknown";
 190         struct dentry *dentry = file->f_dentry;
 191         struct inode *inode = dentry->d_inode;
 192         enum integrity_status status = INTEGRITY_UNKNOWN;
 193         int rc = xattr_len, hash_start = 0;
 194
 195         if (!ima_appraise)
 196                 return 0;
 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 (inode->i_size == 0) {
 207                         iint->flags |= IMA_NEW_FILE;
 208                         status = INTEGRITY_PASS;
 209                 }
 210                 goto out;
 211         }
 212
 213         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 214         if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
 215                 if ((status == INTEGRITY_NOLABEL)
 216                     || (status == INTEGRITY_NOXATTRS))
 217                         cause = "missing-HMAC";
 218                 else if (status == INTEGRITY_FAIL)
 219                         cause = "invalid-HMAC";
 220                 goto out;
 221         }
 222         switch (xattr_value->type) {
 223         case IMA_XATTR_DIGEST_NG:
 224                 /* first byte contains algorithm id */
 225                 hash_start = 1;
 226         case IMA_XATTR_DIGEST:
 227                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 228                         cause = "IMA-signature-required";
 229                         status = INTEGRITY_FAIL;
 230                         break;
 231                 }
 232                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 233                                 iint->ima_hash->length)
 234                         /* xattr length may be longer. md5 hash in previous
 235                            version occupied 20 bytes in xattr, instead of 16
 236                          */
 237                         rc = memcmp(&xattr_value->digest[hash_start],
 238                                     iint->ima_hash->digest,
 239                                     iint->ima_hash->length);
 240                 else
 241                         rc = -EINVAL;
 242                 if (rc) {
 243                         cause = "invalid-hash";
 244                         status = INTEGRITY_FAIL;
 245                         break;
 246                 }
 247                 status = INTEGRITY_PASS;
 248                 break;
 249         case EVM_IMA_XATTR_DIGSIG:
 250                 iint->flags |= IMA_DIGSIG;
 251                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 252                                              (const char *)xattr_value, rc,
 253                                              iint->ima_hash->digest,
 254                                              iint->ima_hash->length);
 255                 if (rc == -EOPNOTSUPP) {
 256                         status = INTEGRITY_UNKNOWN;
 257                 } else if (rc) {
 258                         cause = "invalid-signature";
 259                         status = INTEGRITY_FAIL;
 260                 } else {
 261                         status = INTEGRITY_PASS;
 262                 }
 263                 break;
 264         default:
 265                 status = INTEGRITY_UNKNOWN;
 266                 cause = "unknown-ima-data";
 267                 break;
 268         }
 269
 270 out:
 271         if (status != INTEGRITY_PASS) {
 272                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 273                     (!xattr_value ||
 274                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 275                         if (!ima_fix_xattr(dentry, iint))
 276                                 status = INTEGRITY_PASS;
 277                 }
 278                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 279                                     op, cause, rc, 0);
 280         } else {
 281                 ima_cache_flags(iint, func);
 282         }
 283         ima_set_cache_status(iint, func, status);
 284         return status;
 285 }
 286
 287 /*
 288  * ima_update_xattr - update 'security.ima' hash value
 289  */
 290 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 291 {
 292         struct dentry *dentry = file->f_dentry;
 293         int rc = 0;
 294
 295         /* do not collect and update hash for digital signatures */
 296         if (iint->flags & IMA_DIGSIG)
 297                 return;
 298
 299         rc = ima_collect_measurement(iint, file, NULL, NULL);
 300         if (rc < 0)
 301                 return;
 302
 303         ima_fix_xattr(dentry, iint);
 304 }
 305
 306 /**
 307  * ima_inode_post_setattr - reflect file metadata changes
 308  * @dentry: pointer to the affected dentry
 309  *
 310  * Changes to a dentry's metadata might result in needing to appraise.
 311  *
 312  * This function is called from notify_change(), which expects the caller
 313  * to lock the inode's i_mutex.
 314  */
 315 void ima_inode_post_setattr(struct dentry *dentry)
 316 {
 317         struct inode *inode = dentry->d_inode;
 318         struct integrity_iint_cache *iint;
 319         int must_appraise, rc;
 320
 321         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode)
 322             || !inode->i_op->removexattr)
 323                 return;
 324
 325         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 326         iint = integrity_iint_find(inode);
 327         if (iint) {
 328                 iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
 329                                  IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
 330                                  IMA_ACTION_FLAGS);
 331                 if (must_appraise)
 332                         iint->flags |= IMA_APPRAISE;
 333         }
 334         if (!must_appraise)
 335                 rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
 336         return;
 337 }
 338
 339 /*
 340  * ima_protect_xattr - protect 'security.ima'
 341  *
 342  * Ensure that not just anyone can modify or remove 'security.ima'.
 343  */
 344 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 345                              const void *xattr_value, size_t xattr_value_len)
 346 {
 347         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 348                 if (!capable(CAP_SYS_ADMIN))
 349                         return -EPERM;
 350                 return 1;
 351         }
 352         return 0;
 353 }
 354
 355 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 356 {
 357         struct integrity_iint_cache *iint;
 358
 359         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode))
 360                 return;
 361
 362         iint = integrity_iint_find(inode);
 363         if (!iint)
 364                 return;
 365
 366         iint->flags &= ~IMA_DONE_MASK;
 367         if (digsig)
 368                 iint->flags |= IMA_DIGSIG;
 369         return;
 370 }
 371
 372 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 373                        const void *xattr_value, size_t xattr_value_len)
 374 {
 375         const struct evm_ima_xattr_data *xvalue = xattr_value;
 376         int result;
 377
 378         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 379                                    xattr_value_len);
 380         if (result == 1) {
 381                 ima_reset_appraise_flags(dentry->d_inode,
 382                          (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0);
 383                 result = 0;
 384         }
 385         return result;
 386 }
 387
 388 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 389 {
 390         int result;
 391
 392         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 393         if (result == 1) {
 394                 ima_reset_appraise_flags(dentry->d_inode, 0);
 395                 result = 0;
 396         }
 397         return result;
 398 }