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