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, enum ima_hooks func, int mask)
  38 {
  39         if (!ima_appraise)
  40                 return 0;
  41
  42         return ima_match_policy(inode, func, mask, IMA_APPRAISE);
  43 }
  44
  45 static void ima_fix_xattr(struct dentry *dentry,
  46                           struct integrity_iint_cache *iint)
  47 {
  48         iint->ima_xattr.type = IMA_XATTR_DIGEST;
  49         __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA, (u8 *)&iint->ima_xattr,
  50                               sizeof iint->ima_xattr, 0);
  51 }
  52
  53 /*
  54  * ima_appraise_measurement - appraise file measurement
  55  *
  56  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
  57  * Assuming success, compare the xattr hash with the collected measurement.
  58  *
  59  * Return 0 on success, error code otherwise
  60  */
  61 int ima_appraise_measurement(struct integrity_iint_cache *iint,
  62                              struct file *file, const unsigned char *filename)
  63 {
  64         struct dentry *dentry = file->f_dentry;
  65         struct inode *inode = dentry->d_inode;
  66         struct evm_ima_xattr_data *xattr_value = NULL;
  67         enum integrity_status status = INTEGRITY_UNKNOWN;
  68         const char *op = "appraise_data";
  69         char *cause = "unknown";
  70         int rc;
  71
  72         if (!ima_appraise)
  73                 return 0;
  74         if (!inode->i_op->getxattr)
  75                 return INTEGRITY_UNKNOWN;
  76
  77         if (iint->flags & IMA_APPRAISED)
  78                 return iint->ima_status;
  79
  80         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)&xattr_value,
  81                                 0, GFP_NOFS);
  82         if (rc <= 0) {
  83                 if (rc && rc != -ENODATA)
  84                         goto out;
  85
  86                 cause = "missing-hash";
  87                 status =
  88                     (inode->i_size == 0) ? INTEGRITY_PASS : INTEGRITY_NOLABEL;
  89                 goto out;
  90         }
  91
  92         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
  93         if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
  94                 if ((status == INTEGRITY_NOLABEL)
  95                     || (status == INTEGRITY_NOXATTRS))
  96                         cause = "missing-HMAC";
  97                 else if (status == INTEGRITY_FAIL)
  98                         cause = "invalid-HMAC";
  99                 goto out;
 100         }
 101
 102         switch (xattr_value->type) {
 103         case IMA_XATTR_DIGEST:
 104                 rc = memcmp(xattr_value->digest, iint->ima_xattr.digest,
 105                             IMA_DIGEST_SIZE);
 106                 if (rc) {
 107                         cause = "invalid-hash";
 108                         status = INTEGRITY_FAIL;
 109                         print_hex_dump_bytes("security.ima: ", DUMP_PREFIX_NONE,
 110                                              xattr_value, sizeof(*xattr_value));
 111                         print_hex_dump_bytes("collected: ", DUMP_PREFIX_NONE,
 112                                              (u8 *)&iint->ima_xattr,
 113                                              sizeof iint->ima_xattr);
 114                         break;
 115                 }
 116                 status = INTEGRITY_PASS;
 117                 break;
 118         case EVM_IMA_XATTR_DIGSIG:
 119                 iint->flags |= IMA_DIGSIG;
 120                 rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 121                                              xattr_value->digest, rc - 1,
 122                                              iint->ima_xattr.digest,
 123                                              IMA_DIGEST_SIZE);
 124                 if (rc == -EOPNOTSUPP) {
 125                         status = INTEGRITY_UNKNOWN;
 126                 } else if (rc) {
 127                         cause = "invalid-signature";
 128                         status = INTEGRITY_FAIL;
 129                 } else {
 130                         status = INTEGRITY_PASS;
 131                 }
 132                 break;
 133         default:
 134                 status = INTEGRITY_UNKNOWN;
 135                 cause = "unknown-ima-data";
 136                 break;
 137         }
 138
 139 out:
 140         if (status != INTEGRITY_PASS) {
 141                 if ((ima_appraise & IMA_APPRAISE_FIX) &&
 142                     (!xattr_value ||
 143                      xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 144                         ima_fix_xattr(dentry, iint);
 145                         status = INTEGRITY_PASS;
 146                 }
 147                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 148                                     op, cause, rc, 0);
 149         } else {
 150                 iint->flags |= IMA_APPRAISED;
 151         }
 152         iint->ima_status = status;
 153         kfree(xattr_value);
 154         return status;
 155 }
 156
 157 /*
 158  * ima_update_xattr - update 'security.ima' hash value
 159  */
 160 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 161 {
 162         struct dentry *dentry = file->f_dentry;
 163         int rc = 0;
 164
 165         /* do not collect and update hash for digital signatures */
 166         if (iint->flags & IMA_DIGSIG)
 167                 return;
 168
 169         rc = ima_collect_measurement(iint, file);
 170         if (rc < 0)
 171                 return;
 172
 173         ima_fix_xattr(dentry, iint);
 174 }
 175
 176 /**
 177  * ima_inode_post_setattr - reflect file metadata changes
 178  * @dentry: pointer to the affected dentry
 179  *
 180  * Changes to a dentry's metadata might result in needing to appraise.
 181  *
 182  * This function is called from notify_change(), which expects the caller
 183  * to lock the inode's i_mutex.
 184  */
 185 void ima_inode_post_setattr(struct dentry *dentry)
 186 {
 187         struct inode *inode = dentry->d_inode;
 188         struct integrity_iint_cache *iint;
 189         int must_appraise, rc;
 190
 191         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode)
 192             || !inode->i_op->removexattr)
 193                 return;
 194
 195         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 196         iint = integrity_iint_find(inode);
 197         if (iint) {
 198                 if (must_appraise)
 199                         iint->flags |= IMA_APPRAISE;
 200                 else
 201                         iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED);
 202         }
 203         if (!must_appraise)
 204                 rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
 205         return;
 206 }
 207
 208 /*
 209  * ima_protect_xattr - protect 'security.ima'
 210  *
 211  * Ensure that not just anyone can modify or remove 'security.ima'.
 212  */
 213 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 214                              const void *xattr_value, size_t xattr_value_len)
 215 {
 216         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 217                 if (!capable(CAP_SYS_ADMIN))
 218                         return -EPERM;
 219                 return 1;
 220         }
 221         return 0;
 222 }
 223
 224 static void ima_reset_appraise_flags(struct inode *inode)
 225 {
 226         struct integrity_iint_cache *iint;
 227
 228         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode))
 229                 return;
 230
 231         iint = integrity_iint_find(inode);
 232         if (!iint)
 233                 return;
 234
 235         iint->flags &= ~IMA_DONE_MASK;
 236         return;
 237 }
 238
 239 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 240                        const void *xattr_value, size_t xattr_value_len)
 241 {
 242         int result;
 243
 244         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 245                                    xattr_value_len);
 246         if (result == 1) {
 247                 ima_reset_appraise_flags(dentry->d_inode);
 248                 result = 0;
 249         }
 250         return result;
 251 }
 252
 253 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 254 {
 255         int result;
 256
 257         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 258         if (result == 1) {
 259                 ima_reset_appraise_flags(dentry->d_inode);
 260                 result = 0;
 261         }
 262         return result;
 263 }