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