security/integrity/evm/evm_crypto.c

   1 /*
   2  * Copyright (C) 2005-2010 IBM Corporation
   3  *
   4  * Authors:
   5  * Mimi Zohar <zohar@us.ibm.com>
   6  * Kylene Hall <kjhall@us.ibm.com>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation, version 2 of the License.
  11  *
  12  * File: evm_crypto.c
  13  *       Using root's kernel master key (kmk), calculate the HMAC
  14  */
  15
  16 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  17
  18 #include <linux/module.h>
  19 #include <linux/crypto.h>
  20 #include <linux/xattr.h>
  21 #include <keys/encrypted-type.h>
  22 #include <crypto/hash.h>
  23 #include "evm.h"
  24
  25 #define EVMKEY "evm-key"
  26 #define MAX_KEY_SIZE 128
  27 static unsigned char evmkey[MAX_KEY_SIZE];
  28 static int evmkey_len = MAX_KEY_SIZE;
  29
  30 struct crypto_shash *hmac_tfm;
  31 struct crypto_shash *hash_tfm;
  32
  33 static DEFINE_MUTEX(mutex);
  34
  35 static struct shash_desc *init_desc(char type)
  36 {
  37         long rc;
  38         char *algo;
  39         struct crypto_shash **tfm;
  40         struct shash_desc *desc;
  41
  42         if (type == EVM_XATTR_HMAC) {
  43                 tfm = &hmac_tfm;
  44                 algo = evm_hmac;
  45         } else {
  46                 tfm = &hash_tfm;
  47                 algo = evm_hash;
  48         }
  49
  50         if (*tfm == NULL) {
  51                 mutex_lock(&mutex);
  52                 if (*tfm)
  53                         goto out;
  54                 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
  55                 if (IS_ERR(*tfm)) {
  56                         rc = PTR_ERR(*tfm);
  57                         pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
  58                         *tfm = NULL;
  59                         mutex_unlock(&mutex);
  60                         return ERR_PTR(rc);
  61                 }
  62                 if (type == EVM_XATTR_HMAC) {
  63                         rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
  64                         if (rc) {
  65                                 crypto_free_shash(*tfm);
  66                                 *tfm = NULL;
  67                                 mutex_unlock(&mutex);
  68                                 return ERR_PTR(rc);
  69                         }
  70                 }
  71 out:
  72                 mutex_unlock(&mutex);
  73         }
  74
  75         desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
  76                         GFP_KERNEL);
  77         if (!desc)
  78                 return ERR_PTR(-ENOMEM);
  79
  80         desc->tfm = *tfm;
  81         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
  82
  83         rc = crypto_shash_init(desc);
  84         if (rc) {
  85                 kfree(desc);
  86                 return ERR_PTR(rc);
  87         }
  88         return desc;
  89 }
  90
  91 /* Protect against 'cutting & pasting' security.evm xattr, include inode
  92  * specific info.
  93  *
  94  * (Additional directory/file metadata needs to be added for more complete
  95  * protection.)
  96  */
  97 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
  98                           char *digest)
  99 {
 100         struct h_misc {
 101                 unsigned long ino;
 102                 __u32 generation;
 103                 uid_t uid;
 104                 gid_t gid;
 105                 umode_t mode;
 106         } hmac_misc;
 107
 108         memset(&hmac_misc, 0, sizeof(hmac_misc));
 109         hmac_misc.ino = inode->i_ino;
 110         hmac_misc.generation = inode->i_generation;
 111         hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 112         hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 113         hmac_misc.mode = inode->i_mode;
 114         crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 115         if (evm_hmac_attrs & EVM_ATTR_FSUUID)
 116                 crypto_shash_update(desc, inode->i_sb->s_uuid,
 117                                     sizeof(inode->i_sb->s_uuid));
 118         crypto_shash_final(desc, digest);
 119 }
 120
 121 /*
 122  * Calculate the HMAC value across the set of protected security xattrs.
 123  *
 124  * Instead of retrieving the requested xattr, for performance, calculate
 125  * the hmac using the requested xattr value. Don't alloc/free memory for
 126  * each xattr, but attempt to re-use the previously allocated memory.
 127  */
 128 static int evm_calc_hmac_or_hash(struct dentry *dentry,
 129                                 const char *req_xattr_name,
 130                                 const char *req_xattr_value,
 131                                 size_t req_xattr_value_len,
 132                                 char type, char *digest)
 133 {
 134         struct inode *inode = d_backing_inode(dentry);
 135         struct shash_desc *desc;
 136         char **xattrname;
 137         size_t xattr_size = 0;
 138         char *xattr_value = NULL;
 139         int error;
 140         int size;
 141
 142         if (!inode->i_op->getxattr)
 143                 return -EOPNOTSUPP;
 144         desc = init_desc(type);
 145         if (IS_ERR(desc))
 146                 return PTR_ERR(desc);
 147
 148         error = -ENODATA;
 149         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 150                 if ((req_xattr_name && req_xattr_value)
 151                     && !strcmp(*xattrname, req_xattr_name)) {
 152                         error = 0;
 153                         crypto_shash_update(desc, (const u8 *)req_xattr_value,
 154                                              req_xattr_value_len);
 155                         continue;
 156                 }
 157                 size = vfs_getxattr_alloc(dentry, *xattrname,
 158                                           &xattr_value, xattr_size, GFP_NOFS);
 159                 if (size == -ENOMEM) {
 160                         error = -ENOMEM;
 161                         goto out;
 162                 }
 163                 if (size < 0)
 164                         continue;
 165
 166                 error = 0;
 167                 xattr_size = size;
 168                 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 169         }
 170         hmac_add_misc(desc, inode, digest);
 171
 172 out:
 173         kfree(xattr_value);
 174         kfree(desc);
 175         return error;
 176 }
 177
 178 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 179                   const char *req_xattr_value, size_t req_xattr_value_len,
 180                   char *digest)
 181 {
 182         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 183                                 req_xattr_value_len, EVM_XATTR_HMAC, digest);
 184 }
 185
 186 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 187                   const char *req_xattr_value, size_t req_xattr_value_len,
 188                   char *digest)
 189 {
 190         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 191                                 req_xattr_value_len, IMA_XATTR_DIGEST, digest);
 192 }
 193
 194 /*
 195  * Calculate the hmac and update security.evm xattr
 196  *
 197  * Expects to be called with i_mutex locked.
 198  */
 199 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 200                         const char *xattr_value, size_t xattr_value_len)
 201 {
 202         struct inode *inode = d_backing_inode(dentry);
 203         struct evm_ima_xattr_data xattr_data;
 204         int rc = 0;
 205
 206         rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 207                            xattr_value_len, xattr_data.digest);
 208         if (rc == 0) {
 209                 xattr_data.type = EVM_XATTR_HMAC;
 210                 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 211                                            &xattr_data,
 212                                            sizeof(xattr_data), 0);
 213         } else if (rc == -ENODATA && inode->i_op->removexattr) {
 214                 rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM);
 215         }
 216         return rc;
 217 }
 218
 219 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 220                   char *hmac_val)
 221 {
 222         struct shash_desc *desc;
 223
 224         desc = init_desc(EVM_XATTR_HMAC);
 225         if (IS_ERR(desc)) {
 226                 pr_info("init_desc failed\n");
 227                 return PTR_ERR(desc);
 228         }
 229
 230         crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 231         hmac_add_misc(desc, inode, hmac_val);
 232         kfree(desc);
 233         return 0;
 234 }
 235
 236 /*
 237  * Get the key from the TPM for the SHA1-HMAC
 238  */
 239 int evm_init_key(void)
 240 {
 241         struct key *evm_key;
 242         struct encrypted_key_payload *ekp;
 243         int rc = 0;
 244
 245         evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 246         if (IS_ERR(evm_key))
 247                 return -ENOENT;
 248
 249         down_read(&evm_key->sem);
 250         ekp = evm_key->payload.data;
 251         if (ekp->decrypted_datalen > MAX_KEY_SIZE) {
 252                 rc = -EINVAL;
 253                 goto out;
 254         }
 255         memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen);
 256 out:
 257         /* burn the original key contents */
 258         memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 259         up_read(&evm_key->sem);
 260         key_put(evm_key);
 261         return rc;
 262 }