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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  17
  18 #include <linux/module.h>
  19 #include <linux/crypto.h>
  20 #include <linux/xattr.h>
  21 #include <linux/evm.h>
  22 #include <keys/encrypted-type.h>
  23 #include <crypto/hash.h>
  24 #include "evm.h"
  25
  26 #define EVMKEY "evm-key"
  27 #define MAX_KEY_SIZE 128
  28 static unsigned char evmkey[MAX_KEY_SIZE];
  29 static int evmkey_len = MAX_KEY_SIZE;
  30
  31 struct crypto_shash *hmac_tfm;
  32 struct crypto_shash *hash_tfm;
  33
  34 static DEFINE_MUTEX(mutex);
  35
  36 #define EVM_SET_KEY_BUSY 0
  37
  38 static unsigned long evm_set_key_flags;
  39
  40 /**
  41  * evm_set_key() - set EVM HMAC key from the kernel
  42  * @key: pointer to a buffer with the key data
  43  * @size: length of the key data
  44  *
  45  * This function allows setting the EVM HMAC key from the kernel
  46  * without using the "encrypted" key subsystem keys. It can be used
  47  * by the crypto HW kernel module which has its own way of managing
  48  * keys.
  49  *
  50  * key length should be between 32 and 128 bytes long
  51  */
  52 int evm_set_key(void *key, size_t keylen)
  53 {
  54         int rc;
  55
  56         rc = -EBUSY;
  57         if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
  58                 goto busy;
  59         rc = -EINVAL;
  60         if (keylen > MAX_KEY_SIZE)
  61                 goto inval;
  62         memcpy(evmkey, key, keylen);
  63         evm_initialized |= EVM_INIT_HMAC;
  64         pr_info("key initialized\n");
  65         return 0;
  66 inval:
  67         clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
  68 busy:
  69         pr_err("key initialization failed\n");
  70         return rc;
  71 }
  72 EXPORT_SYMBOL_GPL(evm_set_key);
  73
  74 static struct shash_desc *init_desc(char type)
  75 {
  76         long rc;
  77         char *algo;
  78         struct crypto_shash **tfm;
  79         struct shash_desc *desc;
  80
  81         if (type == EVM_XATTR_HMAC) {
  82                 if (!(evm_initialized & EVM_INIT_HMAC)) {
  83                         pr_err("HMAC key is not set\n");
  84                         return ERR_PTR(-ENOKEY);
  85                 }
  86                 tfm = &hmac_tfm;
  87                 algo = evm_hmac;
  88         } else {
  89                 tfm = &hash_tfm;
  90                 algo = evm_hash;
  91         }
  92
  93         if (*tfm == NULL) {
  94                 mutex_lock(&mutex);
  95                 if (*tfm)
  96                         goto out;
  97                 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
  98                 if (IS_ERR(*tfm)) {
  99                         rc = PTR_ERR(*tfm);
 100                         pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
 101                         *tfm = NULL;
 102                         mutex_unlock(&mutex);
 103                         return ERR_PTR(rc);
 104                 }
 105                 if (type == EVM_XATTR_HMAC) {
 106                         rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
 107                         if (rc) {
 108                                 crypto_free_shash(*tfm);
 109                                 *tfm = NULL;
 110                                 mutex_unlock(&mutex);
 111                                 return ERR_PTR(rc);
 112                         }
 113                 }
 114 out:
 115                 mutex_unlock(&mutex);
 116         }
 117
 118         desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 119                         GFP_KERNEL);
 120         if (!desc)
 121                 return ERR_PTR(-ENOMEM);
 122
 123         desc->tfm = *tfm;
 124         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 125
 126         rc = crypto_shash_init(desc);
 127         if (rc) {
 128                 kfree(desc);
 129                 return ERR_PTR(rc);
 130         }
 131         return desc;
 132 }
 133
 134 /* Protect against 'cutting & pasting' security.evm xattr, include inode
 135  * specific info.
 136  *
 137  * (Additional directory/file metadata needs to be added for more complete
 138  * protection.)
 139  */
 140 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 141                           char *digest)
 142 {
 143         struct h_misc {
 144                 unsigned long ino;
 145                 __u32 generation;
 146                 uid_t uid;
 147                 gid_t gid;
 148                 umode_t mode;
 149         } hmac_misc;
 150
 151         memset(&hmac_misc, 0, sizeof(hmac_misc));
 152         hmac_misc.ino = inode->i_ino;
 153         hmac_misc.generation = inode->i_generation;
 154         /* The hmac uid and gid must be encoded in the initial user
 155          * namespace (not the filesystems user namespace) as encoding
 156          * them in the filesystems user namespace allows an attack
 157          * where first they are written in an unprivileged fuse mount
 158          * of a filesystem and then the system is tricked to mount the
 159          * filesystem for real on next boot and trust it because
 160          * everything is signed.
 161          */
 162         hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 163         hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 164         hmac_misc.mode = inode->i_mode;
 165         crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 166         if (evm_hmac_attrs & EVM_ATTR_FSUUID)
 167                 crypto_shash_update(desc, inode->i_sb->s_uuid,
 168                                     sizeof(inode->i_sb->s_uuid));
 169         crypto_shash_final(desc, digest);
 170 }
 171
 172 /*
 173  * Calculate the HMAC value across the set of protected security xattrs.
 174  *
 175  * Instead of retrieving the requested xattr, for performance, calculate
 176  * the hmac using the requested xattr value. Don't alloc/free memory for
 177  * each xattr, but attempt to re-use the previously allocated memory.
 178  */
 179 static int evm_calc_hmac_or_hash(struct dentry *dentry,
 180                                 const char *req_xattr_name,
 181                                 const char *req_xattr_value,
 182                                 size_t req_xattr_value_len,
 183                                 char type, char *digest)
 184 {
 185         struct inode *inode = d_backing_inode(dentry);
 186         struct shash_desc *desc;
 187         char **xattrname;
 188         size_t xattr_size = 0;
 189         char *xattr_value = NULL;
 190         int error;
 191         int size;
 192
 193         if (!(inode->i_opflags & IOP_XATTR))
 194                 return -EOPNOTSUPP;
 195
 196         desc = init_desc(type);
 197         if (IS_ERR(desc))
 198                 return PTR_ERR(desc);
 199
 200         error = -ENODATA;
 201         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 202                 if ((req_xattr_name && req_xattr_value)
 203                     && !strcmp(*xattrname, req_xattr_name)) {
 204                         error = 0;
 205                         crypto_shash_update(desc, (const u8 *)req_xattr_value,
 206                                              req_xattr_value_len);
 207                         continue;
 208                 }
 209                 size = vfs_getxattr_alloc(dentry, *xattrname,
 210                                           &xattr_value, xattr_size, GFP_NOFS);
 211                 if (size == -ENOMEM) {
 212                         error = -ENOMEM;
 213                         goto out;
 214                 }
 215                 if (size < 0)
 216                         continue;
 217
 218                 error = 0;
 219                 xattr_size = size;
 220                 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 221         }
 222         hmac_add_misc(desc, inode, digest);
 223
 224 out:
 225         kfree(xattr_value);
 226         kfree(desc);
 227         return error;
 228 }
 229
 230 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 231                   const char *req_xattr_value, size_t req_xattr_value_len,
 232                   char *digest)
 233 {
 234         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 235                                 req_xattr_value_len, EVM_XATTR_HMAC, digest);
 236 }
 237
 238 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 239                   const char *req_xattr_value, size_t req_xattr_value_len,
 240                   char *digest)
 241 {
 242         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 243                                 req_xattr_value_len, IMA_XATTR_DIGEST, digest);
 244 }
 245
 246 /*
 247  * Calculate the hmac and update security.evm xattr
 248  *
 249  * Expects to be called with i_mutex locked.
 250  */
 251 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 252                         const char *xattr_value, size_t xattr_value_len)
 253 {
 254         struct inode *inode = d_backing_inode(dentry);
 255         struct evm_ima_xattr_data xattr_data;
 256         int rc = 0;
 257
 258         rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 259                            xattr_value_len, xattr_data.digest);
 260         if (rc == 0) {
 261                 xattr_data.type = EVM_XATTR_HMAC;
 262                 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 263                                            &xattr_data,
 264                                            sizeof(xattr_data), 0);
 265         } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 266                 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 267         }
 268         return rc;
 269 }
 270
 271 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 272                   char *hmac_val)
 273 {
 274         struct shash_desc *desc;
 275
 276         desc = init_desc(EVM_XATTR_HMAC);
 277         if (IS_ERR(desc)) {
 278                 pr_info("init_desc failed\n");
 279                 return PTR_ERR(desc);
 280         }
 281
 282         crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 283         hmac_add_misc(desc, inode, hmac_val);
 284         kfree(desc);
 285         return 0;
 286 }
 287
 288 /*
 289  * Get the key from the TPM for the SHA1-HMAC
 290  */
 291 int evm_init_key(void)
 292 {
 293         struct key *evm_key;
 294         struct encrypted_key_payload *ekp;
 295         int rc;
 296
 297         evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 298         if (IS_ERR(evm_key))
 299                 return -ENOENT;
 300
 301         down_read(&evm_key->sem);
 302         ekp = evm_key->payload.data[0];
 303
 304         rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
 305
 306         /* burn the original key contents */
 307         memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 308         up_read(&evm_key->sem);
 309         key_put(evm_key);
 310         return rc;
 311 }