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Linux/security/integrity/ima/ima_appraise.c

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

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