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_once("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 type, 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         /* Don't include the inode or generation number in portable
 153          * signatures
 154          */
 155         if (type != EVM_XATTR_PORTABLE_DIGSIG) {
 156                 hmac_misc.ino = inode->i_ino;
 157                 hmac_misc.generation = inode->i_generation;
 158         }
 159         /* The hmac uid and gid must be encoded in the initial user
 160          * namespace (not the filesystems user namespace) as encoding
 161          * them in the filesystems user namespace allows an attack
 162          * where first they are written in an unprivileged fuse mount
 163          * of a filesystem and then the system is tricked to mount the
 164          * filesystem for real on next boot and trust it because
 165          * everything is signed.
 166          */
 167         hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 168         hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 169         hmac_misc.mode = inode->i_mode;
 170         crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 171         if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
 172             type != EVM_XATTR_PORTABLE_DIGSIG)
 173                 crypto_shash_update(desc, &inode->i_sb->s_uuid.b[0],
 174                                     sizeof(inode->i_sb->s_uuid));
 175         crypto_shash_final(desc, digest);
 176 }
 177
 178 /*
 179  * Calculate the HMAC value across the set of protected security xattrs.
 180  *
 181  * Instead of retrieving the requested xattr, for performance, calculate
 182  * the hmac using the requested xattr value. Don't alloc/free memory for
 183  * each xattr, but attempt to re-use the previously allocated memory.
 184  */
 185 static int evm_calc_hmac_or_hash(struct dentry *dentry,
 186                                 const char *req_xattr_name,
 187                                 const char *req_xattr_value,
 188                                 size_t req_xattr_value_len,
 189                                 char type, char *digest)
 190 {
 191         struct inode *inode = d_backing_inode(dentry);
 192         struct shash_desc *desc;
 193         char **xattrname;
 194         size_t xattr_size = 0;
 195         char *xattr_value = NULL;
 196         int error;
 197         int size;
 198         bool ima_present = false;
 199
 200         if (!(inode->i_opflags & IOP_XATTR))
 201                 return -EOPNOTSUPP;
 202
 203         desc = init_desc(type);
 204         if (IS_ERR(desc))
 205                 return PTR_ERR(desc);
 206
 207         error = -ENODATA;
 208         for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 209                 bool is_ima = false;
 210
 211                 if (strcmp(*xattrname, XATTR_NAME_IMA) == 0)
 212                         is_ima = true;
 213
 214                 if ((req_xattr_name && req_xattr_value)
 215                     && !strcmp(*xattrname, req_xattr_name)) {
 216                         error = 0;
 217                         crypto_shash_update(desc, (const u8 *)req_xattr_value,
 218                                              req_xattr_value_len);
 219                         if (is_ima)
 220                                 ima_present = true;
 221                         continue;
 222                 }
 223                 size = vfs_getxattr_alloc(dentry, *xattrname,
 224                                           &xattr_value, xattr_size, GFP_NOFS);
 225                 if (size == -ENOMEM) {
 226                         error = -ENOMEM;
 227                         goto out;
 228                 }
 229                 if (size < 0)
 230                         continue;
 231
 232                 error = 0;
 233                 xattr_size = size;
 234                 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 235                 if (is_ima)
 236                         ima_present = true;
 237         }
 238         hmac_add_misc(desc, inode, type, digest);
 239
 240         /* Portable EVM signatures must include an IMA hash */
 241         if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
 242                 return -EPERM;
 243 out:
 244         kfree(xattr_value);
 245         kfree(desc);
 246         return error;
 247 }
 248
 249 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 250                   const char *req_xattr_value, size_t req_xattr_value_len,
 251                   char *digest)
 252 {
 253         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 254                                req_xattr_value_len, EVM_XATTR_HMAC, digest);
 255 }
 256
 257 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 258                   const char *req_xattr_value, size_t req_xattr_value_len,
 259                   char type, char *digest)
 260 {
 261         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 262                                      req_xattr_value_len, type, digest);
 263 }
 264
 265 static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
 266 {
 267         const struct evm_ima_xattr_data *xattr_data = NULL;
 268         struct integrity_iint_cache *iint;
 269         int rc = 0;
 270
 271         iint = integrity_iint_find(inode);
 272         if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
 273                 return 1;
 274
 275         /* Do this the hard way */
 276         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 277                                 GFP_NOFS);
 278         if (rc <= 0) {
 279                 if (rc == -ENODATA)
 280                         return 0;
 281                 return rc;
 282         }
 283         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
 284                 rc = 1;
 285         else
 286                 rc = 0;
 287
 288         kfree(xattr_data);
 289         return rc;
 290 }
 291
 292
 293 /*
 294  * Calculate the hmac and update security.evm xattr
 295  *
 296  * Expects to be called with i_mutex locked.
 297  */
 298 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 299                         const char *xattr_value, size_t xattr_value_len)
 300 {
 301         struct inode *inode = d_backing_inode(dentry);
 302         struct evm_ima_xattr_data xattr_data;
 303         int rc = 0;
 304
 305         /*
 306          * Don't permit any transformation of the EVM xattr if the signature
 307          * is of an immutable type
 308          */
 309         rc = evm_is_immutable(dentry, inode);
 310         if (rc < 0)
 311                 return rc;
 312         if (rc)
 313                 return -EPERM;
 314
 315         rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 316                            xattr_value_len, xattr_data.digest);
 317         if (rc == 0) {
 318                 xattr_data.type = EVM_XATTR_HMAC;
 319                 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 320                                            &xattr_data,
 321                                            sizeof(xattr_data), 0);
 322         } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 323                 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 324         }
 325         return rc;
 326 }
 327
 328 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 329                   char *hmac_val)
 330 {
 331         struct shash_desc *desc;
 332
 333         desc = init_desc(EVM_XATTR_HMAC);
 334         if (IS_ERR(desc)) {
 335                 pr_info("init_desc failed\n");
 336                 return PTR_ERR(desc);
 337         }
 338
 339         crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 340         hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
 341         kfree(desc);
 342         return 0;
 343 }
 344
 345 /*
 346  * Get the key from the TPM for the SHA1-HMAC
 347  */
 348 int evm_init_key(void)
 349 {
 350         struct key *evm_key;
 351         struct encrypted_key_payload *ekp;
 352         int rc;
 353
 354         evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 355         if (IS_ERR(evm_key))
 356                 return -ENOENT;
 357
 358         down_read(&evm_key->sem);
 359         ekp = evm_key->payload.data[0];
 360
 361         rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
 362
 363         /* burn the original key contents */
 364         memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 365         up_read(&evm_key->sem);
 366         key_put(evm_key);
 367         return rc;
 368 }