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