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;
  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 = inode->i_op->getxattr(dentry, XATTR_NAME_IMA, (u8 *)&xattr_value,
  81                                    sizeof xattr_value);
  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, (u8 *)&xattr_value,
  93                                  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         rc = memcmp(xattr_value.digest, iint->ima_xattr.digest,
 104                     IMA_DIGEST_SIZE);
 105         if (rc) {
 106                 status = INTEGRITY_FAIL;
 107                 cause = "invalid-hash";
 108                 print_hex_dump_bytes("security.ima: ", DUMP_PREFIX_NONE,
 109                                      &xattr_value, sizeof xattr_value);
 110                 print_hex_dump_bytes("collected: ", DUMP_PREFIX_NONE,
 111                                      (u8 *)&iint->ima_xattr,
 112                                      sizeof iint->ima_xattr);
 113                 goto out;
 114         }
 115         status = INTEGRITY_PASS;
 116         iint->flags |= IMA_APPRAISED;
 117 out:
 118         if (status != INTEGRITY_PASS) {
 119                 if (ima_appraise & IMA_APPRAISE_FIX) {
 120                         ima_fix_xattr(dentry, iint);
 121                         status = INTEGRITY_PASS;
 122                 }
 123                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 124                                     op, cause, rc, 0);
 125         }
 126         iint->ima_status = status;
 127         return status;
 128 }
 129
 130 /*
 131  * ima_update_xattr - update 'security.ima' hash value
 132  */
 133 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 134 {
 135         struct dentry *dentry = file->f_dentry;
 136         int rc = 0;
 137
 138         rc = ima_collect_measurement(iint, file);
 139         if (rc < 0)
 140                 return;
 141         ima_fix_xattr(dentry, iint);
 142 }
 143
 144 /**
 145  * ima_inode_post_setattr - reflect file metadata changes
 146  * @dentry: pointer to the affected dentry
 147  *
 148  * Changes to a dentry's metadata might result in needing to appraise.
 149  *
 150  * This function is called from notify_change(), which expects the caller
 151  * to lock the inode's i_mutex.
 152  */
 153 void ima_inode_post_setattr(struct dentry *dentry)
 154 {
 155         struct inode *inode = dentry->d_inode;
 156         struct integrity_iint_cache *iint;
 157         int must_appraise, rc;
 158
 159         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode)
 160             || !inode->i_op->removexattr)
 161                 return;
 162
 163         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 164         iint = integrity_iint_find(inode);
 165         if (iint) {
 166                 if (must_appraise)
 167                         iint->flags |= IMA_APPRAISE;
 168                 else
 169                         iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED);
 170         }
 171         if (!must_appraise)
 172                 rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
 173         return;
 174 }
 175
 176 /*
 177  * ima_protect_xattr - protect 'security.ima'
 178  *
 179  * Ensure that not just anyone can modify or remove 'security.ima'.
 180  */
 181 static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
 182                              const void *xattr_value, size_t xattr_value_len)
 183 {
 184         if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
 185                 if (!capable(CAP_SYS_ADMIN))
 186                         return -EPERM;
 187                 return 1;
 188         }
 189         return 0;
 190 }
 191
 192 static void ima_reset_appraise_flags(struct inode *inode)
 193 {
 194         struct integrity_iint_cache *iint;
 195
 196         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode))
 197                 return;
 198
 199         iint = integrity_iint_find(inode);
 200         if (!iint)
 201                 return;
 202
 203         iint->flags &= ~(IMA_COLLECTED | IMA_APPRAISED | IMA_MEASURED);
 204         return;
 205 }
 206
 207 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 208                        const void *xattr_value, size_t xattr_value_len)
 209 {
 210         int result;
 211
 212         result = ima_protect_xattr(dentry, xattr_name, xattr_value,
 213                                    xattr_value_len);
 214         if (result == 1) {
 215                 ima_reset_appraise_flags(dentry->d_inode);
 216                 result = 0;
 217         }
 218         return result;
 219 }
 220
 221 int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 222 {
 223         int result;
 224
 225         result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 226         if (result == 1) {
 227                 ima_reset_appraise_flags(dentry->d_inode);
 228                 result = 0;
 229         }
 230         return result;
 231 }