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
  19 #include "ima.h"
  20
  21 static int __init default_appraise_setup(char *str)
  22 {
  23         if (strncmp(str, "off", 3) == 0)
  24                 ima_appraise = 0;
  25         else if (strncmp(str, "fix", 3) == 0)
  26                 ima_appraise = IMA_APPRAISE_FIX;
  27         return 1;
  28 }
  29
  30 __setup("ima_appraise=", default_appraise_setup);
  31
  32 /*
  33  * ima_must_appraise - set appraise flag
  34  *
  35  * Return 1 to appraise
  36  */
  37 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
  38 {
  39         if (!ima_appraise)
  40                 return 0;
  41
  42         return ima_match_policy(inode, func, mask, IMA_APPRAISE);
  43 }
  44
  45 static int ima_fix_xattr(struct dentry *dentry,
  46                           struct integrity_iint_cache *iint)
  47 {
  48         iint->ima_xattr.type = IMA_XATTR_DIGEST;
  49         return __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  50                                      (u8 *)&iint->ima_xattr,
  51                                       sizeof(iint->ima_xattr), 0);
  52 }
  53
  54 /*
  55  * ima_appraise_measurement - appraise file measurement
  56  *
  57  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
  58  * Assuming success, compare the xattr hash with the collected measurement.
  59  *
  60  * Return 0 on success, error code otherwise
  61  */
  62 int ima_appraise_measurement(struct integrity_iint_cache *iint,
  63                              struct file *file, const unsigned char *filename)
  64 {
  65         struct dentry *dentry = file->f_dentry;
  66         struct inode *inode = dentry->d_inode;
  67         struct evm_ima_xattr_data *xattr_value = NULL;
  68         enum integrity_status status = INTEGRITY_UNKNOWN;
  69         const char *op = "appraise_data";
  70         char *cause = "unknown";
  71         int rc;
  72
  73         if (!ima_appraise)
  74                 return 0;
  75         if (!inode->i_op->getxattr)
  76                 return INTEGRITY_UNKNOWN;
  77
  78         if (iint->flags & IMA_APPRAISED)
  79                 return iint->ima_status;
  80
  81         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)&xattr_value,
  82                                 0, GFP_NOFS);
  83         if (rc <= 0) {
  84                 if (rc && rc != -ENODATA)
  85                         goto out;
  86
  87                 cause = "missing-hash";
  88                 status =
  89                     (inode->i_size == 0) ? INTEGRITY_PASS : INTEGRITY_NOLABEL;
  90                 goto out;
  91         }
  92
  93         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
  94         if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
  95                 if ((status == INTEGRITY_NOLABEL)
  96                     || (status == INTEGRITY_NOXATTRS))
  97                         cause = "missing-HMAC";
  98                 else if (status == INTEGRITY_FAIL)
  99                         cause = "invalid-HMAC";
 100                 goto out;
 101         }
 102
 103         switch (xattr_value->type) {
 104         case IMA_XATTR_DIGEST:
 105                 rc = memcmp(xattr_value->digest, iint->ima_xattr.digest,
 106                             IMA_DIGEST_SIZE);
 107                 if (rc) {
 108                         cause = "invalid-hash";
 109                         status = INTEGRITY_FAIL;
 110                         break;
 111                 }
 112                 status = INTEGRITY_PASS;
 113                 break;
 114         case EVM_IMA_XATTR_DIGSIG:
 115                 iint->flags |= IMA_DIGSIG;
 116                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 117                                              xattr_value->digest, rc - 1,
 118                                              iint->ima_xattr.digest,
 119                                              IMA_DIGEST_SIZE);
 120                 if (rc == -EOPNOTSUPP) {
 121                         status = INTEGRITY_UNKNOWN;
 122                 } else if (rc) {
 123                         cause = "invalid-signature";
 124                         status = INTEGRITY_FAIL;
 125                 } else {
 126                         status = INTEGRITY_PASS;
 127                 }
 128                 break;
 129         default:
 130                 status = INTEGRITY_UNKNOWN;
 131                 cause = "unknown-ima-data";
 132                 break;
 133         }
 134
 135 out:
 136         if (status != INTEGRITY_PASS) {
 137                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 138                     (!xattr_value ||
 139                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 140                         if (!ima_fix_xattr(dentry, iint))
 141                                 status = INTEGRITY_PASS;
 142                 }
 143                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 144                                     op, cause, rc, 0);
 145         } else {
 146                 iint->flags |= IMA_APPRAISED;
 147         }
 148         iint->ima_status = status;
 149         kfree(xattr_value);
 150         return status;
 151 }
 152
 153 /*
 154  * ima_update_xattr - update 'security.ima' hash value
 155  */
 156 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 157 {
 158         struct dentry *dentry = file->f_dentry;
 159         int rc = 0;
 160
 161         /* do not collect and update hash for digital signatures */
 162         if (iint->flags & IMA_DIGSIG)
 163                 return;
 164
 165         rc = ima_collect_measurement(iint, file);
 166         if (rc < 0)
 167                 return;
 168
 169         ima_fix_xattr(dentry, iint);
 170 }
 171
 172 /**
 173  * ima_inode_post_setattr - reflect file metadata changes
 174  * @dentry: pointer to the affected dentry
 175  *
 176  * Changes to a dentry's metadata might result in needing to appraise.
 177  *
 178  * This function is called from notify_change(), which expects the caller
 179  * to lock the inode's i_mutex.
 180  */
 181 void ima_inode_post_setattr(struct dentry *dentry)
 182 {
 183         struct inode *inode = dentry->d_inode;
 184         struct integrity_iint_cache *iint;
 185         int must_appraise, rc;
 186
 187         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode)
 188             || !inode->i_op->removexattr)
 189                 return;
 190
 191         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 192         iint = integrity_iint_find(inode);
 193         if (iint) {
 194                 if (must_appraise)
 195                         iint->flags |= IMA_APPRAISE;
 196                 else
 197                         iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED);
 198         }
 199         if (!must_appraise)
 200                 rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
 201         return;
 202 }
 203
 204 /*
 205  * ima_protect_xattr - protect 'security.ima'
 206  *
 207  * Ensure that not just anyone can modify or remove 'security.ima'.
 208  */
 209 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 210                              const void *xattr_value, size_t xattr_value_len)
 211 {
 212         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 213                 if (!capable(CAP_SYS_ADMIN))
 214                         return -EPERM;
 215                 return 1;
 216         }
 217         return 0;
 218 }
 219
 220 static void ima_reset_appraise_flags(struct inode *inode)
 221 {
 222         struct integrity_iint_cache *iint;
 223
 224         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode))
 225                 return;
 226
 227         iint = integrity_iint_find(inode);
 228         if (!iint)
 229                 return;
 230
 231         iint->flags &= ~IMA_DONE_MASK;
 232         return;
 233 }
 234
 235 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 236                        const void *xattr_value, size_t xattr_value_len)
 237 {
 238         int result;
 239
 240         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 241                                    xattr_value_len);
 242         if (result == 1) {
 243                 ima_reset_appraise_flags(dentry->d_inode);
 244                 result = 0;
 245         }
 246         return result;
 247 }
 248
 249 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 250 {
 251         int result;
 252
 253         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 254         if (result == 1) {
 255                 ima_reset_appraise_flags(dentry->d_inode);
 256                 result = 0;
 257         }
 258         return result;
 259 }