security/integrity/ima/ima_appraise.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2011 IBM Corporation
   4  *
   5  * Author:
   6  * Mimi Zohar <zohar@us.ibm.com>
   7  */
   8 #include <linux/init.h>
   9 #include <linux/file.h>
  10 #include <linux/fs.h>
  11 #include <linux/xattr.h>
  12 #include <linux/magic.h>
  13 #include <linux/ima.h>
  14 #include <linux/evm.h>
  15
  16 #include "ima.h"
  17
  18 static int __init default_appraise_setup(char *str)
  19 {
  20 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
  21         if (strncmp(str, "off", 3) == 0)
  22                 ima_appraise = 0;
  23         else if (strncmp(str, "log", 3) == 0)
  24                 ima_appraise = IMA_APPRAISE_LOG;
  25         else if (strncmp(str, "fix", 3) == 0)
  26                 ima_appraise = IMA_APPRAISE_FIX;
  27 #endif
  28         return 1;
  29 }
  30
  31 __setup("ima_appraise=", default_appraise_setup);
  32
  33 /*
  34  * is_ima_appraise_enabled - return appraise status
  35  *
  36  * Only return enabled, if not in ima_appraise="fix" or "log" modes.
  37  */
  38 bool is_ima_appraise_enabled(void)
  39 {
  40         return ima_appraise & IMA_APPRAISE_ENFORCE;
  41 }
  42
  43 /*
  44  * ima_must_appraise - set appraise flag
  45  *
  46  * Return 1 to appraise or hash
  47  */
  48 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
  49 {
  50         u32 secid;
  51
  52         if (!ima_appraise)
  53                 return 0;
  54
  55         security_task_getsecid(current, &secid);
  56         return ima_match_policy(inode, current_cred(), secid, func, mask,
  57                                 IMA_APPRAISE | IMA_HASH, NULL, NULL);
  58 }
  59
  60 static int ima_fix_xattr(struct dentry *dentry,
  61                          struct integrity_iint_cache *iint)
  62 {
  63         int rc, offset;
  64         u8 algo = iint->ima_hash->algo;
  65
  66         if (algo <= HASH_ALGO_SHA1) {
  67                 offset = 1;
  68                 iint->ima_hash->xattr.sha1.type = IMA_XATTR_DIGEST;
  69         } else {
  70                 offset = 0;
  71                 iint->ima_hash->xattr.ng.type = IMA_XATTR_DIGEST_NG;
  72                 iint->ima_hash->xattr.ng.algo = algo;
  73         }
  74         rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  75                                    &iint->ima_hash->xattr.data[offset],
  76                                    (sizeof(iint->ima_hash->xattr) - offset) +
  77                                    iint->ima_hash->length, 0);
  78         return rc;
  79 }
  80
  81 /* Return specific func appraised cached result */
  82 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
  83                                            enum ima_hooks func)
  84 {
  85         switch (func) {
  86         case MMAP_CHECK:
  87                 return iint->ima_mmap_status;
  88         case BPRM_CHECK:
  89                 return iint->ima_bprm_status;
  90         case CREDS_CHECK:
  91                 return iint->ima_creds_status;
  92         case FILE_CHECK:
  93         case POST_SETATTR:
  94                 return iint->ima_file_status;
  95         case MODULE_CHECK ... MAX_CHECK - 1:
  96         default:
  97                 return iint->ima_read_status;
  98         }
  99 }
 100
 101 static void ima_set_cache_status(struct integrity_iint_cache *iint,
 102                                  enum ima_hooks func,
 103                                  enum integrity_status status)
 104 {
 105         switch (func) {
 106         case MMAP_CHECK:
 107                 iint->ima_mmap_status = status;
 108                 break;
 109         case BPRM_CHECK:
 110                 iint->ima_bprm_status = status;
 111                 break;
 112         case CREDS_CHECK:
 113                 iint->ima_creds_status = status;
 114                 break;
 115         case FILE_CHECK:
 116         case POST_SETATTR:
 117                 iint->ima_file_status = status;
 118                 break;
 119         case MODULE_CHECK ... MAX_CHECK - 1:
 120         default:
 121                 iint->ima_read_status = status;
 122                 break;
 123         }
 124 }
 125
 126 static void ima_cache_flags(struct integrity_iint_cache *iint,
 127                              enum ima_hooks func)
 128 {
 129         switch (func) {
 130         case MMAP_CHECK:
 131                 iint->flags |= (IMA_MMAP_APPRAISED | IMA_APPRAISED);
 132                 break;
 133         case BPRM_CHECK:
 134                 iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 135                 break;
 136         case CREDS_CHECK:
 137                 iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
 138                 break;
 139         case FILE_CHECK:
 140         case POST_SETATTR:
 141                 iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
 142                 break;
 143         case MODULE_CHECK ... MAX_CHECK - 1:
 144         default:
 145                 iint->flags |= (IMA_READ_APPRAISED | IMA_APPRAISED);
 146                 break;
 147         }
 148 }
 149
 150 enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 151                                  int xattr_len)
 152 {
 153         struct signature_v2_hdr *sig;
 154         enum hash_algo ret;
 155
 156         if (!xattr_value || xattr_len < 2)
 157                 /* return default hash algo */
 158                 return ima_hash_algo;
 159
 160         switch (xattr_value->type) {
 161         case EVM_IMA_XATTR_DIGSIG:
 162                 sig = (typeof(sig))xattr_value;
 163                 if (sig->version != 2 || xattr_len <= sizeof(*sig))
 164                         return ima_hash_algo;
 165                 return sig->hash_algo;
 166                 break;
 167         case IMA_XATTR_DIGEST_NG:
 168                 /* first byte contains algorithm id */
 169                 ret = xattr_value->data[0];
 170                 if (ret < HASH_ALGO__LAST)
 171                         return ret;
 172                 break;
 173         case IMA_XATTR_DIGEST:
 174                 /* this is for backward compatibility */
 175                 if (xattr_len == 21) {
 176                         unsigned int zero = 0;
 177                         if (!memcmp(&xattr_value->data[16], &zero, 4))
 178                                 return HASH_ALGO_MD5;
 179                         else
 180                                 return HASH_ALGO_SHA1;
 181                 } else if (xattr_len == 17)
 182                         return HASH_ALGO_MD5;
 183                 break;
 184         }
 185
 186         /* return default hash algo */
 187         return ima_hash_algo;
 188 }
 189
 190 int ima_read_xattr(struct dentry *dentry,
 191                    struct evm_ima_xattr_data **xattr_value)
 192 {
 193         ssize_t ret;
 194
 195         ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
 196                                  0, GFP_NOFS);
 197         if (ret == -EOPNOTSUPP)
 198                 ret = 0;
 199         return ret;
 200 }
 201
 202 /*
 203  * ima_appraise_measurement - appraise file measurement
 204  *
 205  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
 206  * Assuming success, compare the xattr hash with the collected measurement.
 207  *
 208  * Return 0 on success, error code otherwise
 209  */
 210 int ima_appraise_measurement(enum ima_hooks func,
 211                              struct integrity_iint_cache *iint,
 212                              struct file *file, const unsigned char *filename,
 213                              struct evm_ima_xattr_data *xattr_value,
 214                              int xattr_len)
 215 {
 216         static const char op[] = "appraise_data";
 217         const char *cause = "unknown";
 218         struct dentry *dentry = file_dentry(file);
 219         struct inode *inode = d_backing_inode(dentry);
 220         enum integrity_status status = INTEGRITY_UNKNOWN;
 221         int rc = xattr_len, hash_start = 0;
 222
 223         if (!(inode->i_opflags & IOP_XATTR))
 224                 return INTEGRITY_UNKNOWN;
 225
 226         if (rc <= 0) {
 227                 if (rc && rc != -ENODATA)
 228                         goto out;
 229
 230                 cause = iint->flags & IMA_DIGSIG_REQUIRED ?
 231                                 "IMA-signature-required" : "missing-hash";
 232                 status = INTEGRITY_NOLABEL;
 233                 if (file->f_mode & FMODE_CREATED)
 234                         iint->flags |= IMA_NEW_FILE;
 235                 if ((iint->flags & IMA_NEW_FILE) &&
 236                     (!(iint->flags & IMA_DIGSIG_REQUIRED) ||
 237                      (inode->i_size == 0)))
 238                         status = INTEGRITY_PASS;
 239                 goto out;
 240         }
 241
 242         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
 243         switch (status) {
 244         case INTEGRITY_PASS:
 245         case INTEGRITY_PASS_IMMUTABLE:
 246         case INTEGRITY_UNKNOWN:
 247                 break;
 248         case INTEGRITY_NOXATTRS:        /* No EVM protected xattrs. */
 249         case INTEGRITY_NOLABEL:         /* No security.evm xattr. */
 250                 cause = "missing-HMAC";
 251                 goto out;
 252         case INTEGRITY_FAIL:            /* Invalid HMAC/signature. */
 253                 cause = "invalid-HMAC";
 254                 goto out;
 255         default:
 256                 WARN_ONCE(true, "Unexpected integrity status %d\n", status);
 257         }
 258
 259         switch (xattr_value->type) {
 260         case IMA_XATTR_DIGEST_NG:
 261                 /* first byte contains algorithm id */
 262                 hash_start = 1;
 263                 /* fall through */
 264         case IMA_XATTR_DIGEST:
 265                 if (iint->flags & IMA_DIGSIG_REQUIRED) {
 266                         cause = "IMA-signature-required";
 267                         status = INTEGRITY_FAIL;
 268                         break;
 269                 }
 270                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 271                 if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 272                                 iint->ima_hash->length)
 273                         /* xattr length may be longer. md5 hash in previous
 274                            version occupied 20 bytes in xattr, instead of 16
 275                          */
 276                         rc = memcmp(&xattr_value->data[hash_start],
 277                                     iint->ima_hash->digest,
 278                                     iint->ima_hash->length);
 279                 else
 280                         rc = -EINVAL;
 281                 if (rc) {
 282                         cause = "invalid-hash";
 283                         status = INTEGRITY_FAIL;
 284                         break;
 285                 }
 286                 status = INTEGRITY_PASS;
 287                 break;
 288         case EVM_IMA_XATTR_DIGSIG:
 289                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 290                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 291                                              (const char *)xattr_value,
 292                                              xattr_len,
 293                                              iint->ima_hash->digest,
 294                                              iint->ima_hash->length);
 295                 if (rc == -EOPNOTSUPP) {
 296                         status = INTEGRITY_UNKNOWN;
 297                         break;
 298                 }
 299                 if (IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING) && rc &&
 300                     func == KEXEC_KERNEL_CHECK)
 301                         rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
 302                                                      (const char *)xattr_value,
 303                                                      xattr_len,
 304                                                      iint->ima_hash->digest,
 305                                                      iint->ima_hash->length);
 306                 if (rc) {
 307                         cause = "invalid-signature";
 308                         status = INTEGRITY_FAIL;
 309                 } else {
 310                         status = INTEGRITY_PASS;
 311                 }
 312                 break;
 313         default:
 314                 status = INTEGRITY_UNKNOWN;
 315                 cause = "unknown-ima-data";
 316                 break;
 317         }
 318
 319 out:
 320         /*
 321          * File signatures on some filesystems can not be properly verified.
 322          * When such filesystems are mounted by an untrusted mounter or on a
 323          * system not willing to accept such a risk, fail the file signature
 324          * verification.
 325          */
 326         if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
 327             ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
 328              (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 329                 status = INTEGRITY_FAIL;
 330                 cause = "unverifiable-signature";
 331                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 332                                     op, cause, rc, 0);
 333         } else if (status != INTEGRITY_PASS) {
 334                 /* Fix mode, but don't replace file signatures. */
 335                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 336                     (!xattr_value ||
 337                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 338                         if (!ima_fix_xattr(dentry, iint))
 339                                 status = INTEGRITY_PASS;
 340                 }
 341
 342                 /* Permit new files with file signatures, but without data. */
 343                 if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
 344                     xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
 345                         status = INTEGRITY_PASS;
 346                 }
 347
 348                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 349                                     op, cause, rc, 0);
 350         } else {
 351                 ima_cache_flags(iint, func);
 352         }
 353
 354         ima_set_cache_status(iint, func, status);
 355         return status;
 356 }
 357
 358 /*
 359  * ima_update_xattr - update 'security.ima' hash value
 360  */
 361 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 362 {
 363         struct dentry *dentry = file_dentry(file);
 364         int rc = 0;
 365
 366         /* do not collect and update hash for digital signatures */
 367         if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 368                 return;
 369
 370         if ((iint->ima_file_status != INTEGRITY_PASS) &&
 371             !(iint->flags & IMA_HASH))
 372                 return;
 373
 374         rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
 375         if (rc < 0)
 376                 return;
 377
 378         inode_lock(file_inode(file));
 379         ima_fix_xattr(dentry, iint);
 380         inode_unlock(file_inode(file));
 381 }
 382
 383 /**
 384  * ima_inode_post_setattr - reflect file metadata changes
 385  * @dentry: pointer to the affected dentry
 386  *
 387  * Changes to a dentry's metadata might result in needing to appraise.
 388  *
 389  * This function is called from notify_change(), which expects the caller
 390  * to lock the inode's i_mutex.
 391  */
 392 void ima_inode_post_setattr(struct dentry *dentry)
 393 {
 394         struct inode *inode = d_backing_inode(dentry);
 395         struct integrity_iint_cache *iint;
 396         int action;
 397
 398         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 399             || !(inode->i_opflags & IOP_XATTR))
 400                 return;
 401
 402         action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 403         if (!action)
 404                 __vfs_removexattr(dentry, XATTR_NAME_IMA);
 405         iint = integrity_iint_find(inode);
 406         if (iint) {
 407                 set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
 408                 if (!action)
 409                         clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 410         }
 411 }
 412
 413 /*
 414  * ima_protect_xattr - protect 'security.ima'
 415  *
 416  * Ensure that not just anyone can modify or remove 'security.ima'.
 417  */
 418 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 419                              const void *xattr_value, size_t xattr_value_len)
 420 {
 421         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 422                 if (!capable(CAP_SYS_ADMIN))
 423                         return -EPERM;
 424                 return 1;
 425         }
 426         return 0;
 427 }
 428
 429 static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 430 {
 431         struct integrity_iint_cache *iint;
 432
 433         if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
 434                 return;
 435
 436         iint = integrity_iint_find(inode);
 437         if (!iint)
 438                 return;
 439         iint->measured_pcrs = 0;
 440         set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 441         if (digsig)
 442                 set_bit(IMA_DIGSIG, &iint->atomic_flags);
 443         else
 444                 clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 445 }
 446
 447 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 448                        const void *xattr_value, size_t xattr_value_len)
 449 {
 450         const struct evm_ima_xattr_data *xvalue = xattr_value;
 451         int result;
 452
 453         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 454                                    xattr_value_len);
 455         if (result == 1) {
 456                 if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 457                         return -EINVAL;
 458                 ima_reset_appraise_flags(d_backing_inode(dentry),
 459                         xvalue->type == EVM_IMA_XATTR_DIGSIG);
 460                 result = 0;
 461         }
 462         return result;
 463 }
 464
 465 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 466 {
 467         int result;
 468
 469         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 470         if (result == 1) {
 471                 ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 472                 result = 0;
 473         }
 474         return result;
 475 }