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 <linux/scatterlist.h>
  20 #include <keys/encrypted-type.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 static int init_desc(struct hash_desc *desc)
  29 {
  30         int rc;
  31
  32         desc->tfm = crypto_alloc_hash(evm_hmac, 0, CRYPTO_ALG_ASYNC);
  33         if (IS_ERR(desc->tfm)) {
  34                 pr_info("Can not allocate %s (reason: %ld)\n",
  35                         evm_hmac, PTR_ERR(desc->tfm));
  36                 rc = PTR_ERR(desc->tfm);
  37                 return rc;
  38         }
  39         desc->flags = 0;
  40         rc = crypto_hash_setkey(desc->tfm, evmkey, evmkey_len);
  41         if (rc)
  42                 goto out;
  43         rc = crypto_hash_init(desc);
  44 out:
  45         if (rc)
  46                 crypto_free_hash(desc->tfm);
  47         return rc;
  48 }
  49
  50 /* Protect against 'cutting & pasting' security.evm xattr, include inode
  51  * specific info.
  52  *
  53  * (Additional directory/file metadata needs to be added for more complete
  54  * protection.)
  55  */
  56 static void hmac_add_misc(struct hash_desc *desc, struct inode *inode,
  57                           char *digest)
  58 {
  59         struct h_misc {
  60                 unsigned long ino;
  61                 __u32 generation;
  62                 uid_t uid;
  63                 gid_t gid;
  64                 umode_t mode;
  65         } hmac_misc;
  66         struct scatterlist sg[1];
  67
  68         memset(&hmac_misc, 0, sizeof hmac_misc);
  69         hmac_misc.ino = inode->i_ino;
  70         hmac_misc.generation = inode->i_generation;
  71         hmac_misc.uid = inode->i_uid;
  72         hmac_misc.gid = inode->i_gid;
  73         hmac_misc.mode = inode->i_mode;
  74         sg_init_one(sg, &hmac_misc, sizeof hmac_misc);
  75         crypto_hash_update(desc, sg, sizeof hmac_misc);
  76         crypto_hash_final(desc, digest);
  77 }
  78
  79 /*
  80  * Calculate the HMAC value across the set of protected security xattrs.
  81  *
  82  * Instead of retrieving the requested xattr, for performance, calculate
  83  * the hmac using the requested xattr value. Don't alloc/free memory for
  84  * each xattr, but attempt to re-use the previously allocated memory.
  85  */
  86 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
  87                   const char *req_xattr_value, size_t req_xattr_value_len,
  88                   char *digest)
  89 {
  90         struct inode *inode = dentry->d_inode;
  91         struct hash_desc desc;
  92         struct scatterlist sg[1];
  93         char **xattrname;
  94         size_t xattr_size = 0;
  95         char *xattr_value = NULL;
  96         int error;
  97         int size;
  98
  99         if (!inode->i_op || !inode->i_op->getxattr)
 100                 return -EOPNOTSUPP;
 101         error = init_desc(&desc);
 102         if (error)
 103                 return error;
 104
 105         error = -ENODATA;
 106         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 107                 if ((req_xattr_name && req_xattr_value)
 108                     && !strcmp(*xattrname, req_xattr_name)) {
 109                         error = 0;
 110                         sg_init_one(sg, req_xattr_value, req_xattr_value_len);
 111                         crypto_hash_update(&desc, sg, req_xattr_value_len);
 112                         continue;
 113                 }
 114                 size = vfs_getxattr_alloc(dentry, *xattrname,
 115                                           &xattr_value, xattr_size, GFP_NOFS);
 116                 if (size == -ENOMEM) {
 117                         error = -ENOMEM;
 118                         goto out;
 119                 }
 120                 if (size < 0)
 121                         continue;
 122
 123                 error = 0;
 124                 xattr_size = size;
 125                 sg_init_one(sg, xattr_value, xattr_size);
 126                 crypto_hash_update(&desc, sg, xattr_size);
 127         }
 128         hmac_add_misc(&desc, inode, digest);
 129         kfree(xattr_value);
 130 out:
 131         crypto_free_hash(desc.tfm);
 132         return error;
 133 }
 134
 135 /*
 136  * Calculate the hmac and update security.evm xattr
 137  *
 138  * Expects to be called with i_mutex locked.
 139  */
 140 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 141                         const char *xattr_value, size_t xattr_value_len)
 142 {
 143         struct inode *inode = dentry->d_inode;
 144         struct evm_ima_xattr_data xattr_data;
 145         int rc = 0;
 146
 147         rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 148                            xattr_value_len, xattr_data.digest);
 149         if (rc == 0) {
 150                 xattr_data.type = EVM_XATTR_HMAC;
 151                 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 152                                            &xattr_data,
 153                                            sizeof(xattr_data), 0);
 154         }
 155         else if (rc == -ENODATA)
 156                 rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM);
 157         return rc;
 158 }
 159
 160 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 161                   char *hmac_val)
 162 {
 163         struct hash_desc desc;
 164         struct scatterlist sg[1];
 165         int error;
 166
 167         error = init_desc(&desc);
 168         if (error != 0) {
 169                 printk(KERN_INFO "init_desc failed\n");
 170                 return error;
 171         }
 172
 173         sg_init_one(sg, lsm_xattr->value, lsm_xattr->value_len);
 174         crypto_hash_update(&desc, sg, lsm_xattr->value_len);
 175         hmac_add_misc(&desc, inode, hmac_val);
 176         crypto_free_hash(desc.tfm);
 177         return 0;
 178 }
 179
 180 /*
 181  * Get the key from the TPM for the SHA1-HMAC
 182  */
 183 int evm_init_key(void)
 184 {
 185         struct key *evm_key;
 186         struct encrypted_key_payload *ekp;
 187         int rc = 0;
 188
 189         evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 190         if (IS_ERR(evm_key))
 191                 return -ENOENT;
 192
 193         down_read(&evm_key->sem);
 194         ekp = evm_key->payload.data;
 195         if (ekp->decrypted_datalen > MAX_KEY_SIZE) {
 196                 rc = -EINVAL;
 197                 goto out;
 198         }
 199         memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen);
 200 out:
 201         /* burn the original key contents */
 202         memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 203         up_read(&evm_key->sem);
 204         key_put(evm_key);
 205         return rc;
 206 }