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