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 <crypto/hash_info.h>
  25 #include "evm.h"
  26
  27 #define EVMKEY "evm-key"
  28 #define MAX_KEY_SIZE 128
  29 static unsigned char evmkey[MAX_KEY_SIZE];
  30 static int evmkey_len = MAX_KEY_SIZE;
  31
  32 struct crypto_shash *hmac_tfm;
  33 static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
  34
  35 static DEFINE_MUTEX(mutex);
  36
  37 #define EVM_SET_KEY_BUSY 0
  38
  39 static unsigned long evm_set_key_flags;
  40
  41 static char * const evm_hmac = "hmac(sha1)";
  42
  43 /**
  44  * evm_set_key() - set EVM HMAC key from the kernel
  45  * @key: pointer to a buffer with the key data
  46  * @size: length of the key data
  47  *
  48  * This function allows setting the EVM HMAC key from the kernel
  49  * without using the "encrypted" key subsystem keys. It can be used
  50  * by the crypto HW kernel module which has its own way of managing
  51  * keys.
  52  *
  53  * key length should be between 32 and 128 bytes long
  54  */
  55 int evm_set_key(void *key, size_t keylen)
  56 {
  57         int rc;
  58
  59         rc = -EBUSY;
  60         if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
  61                 goto busy;
  62         rc = -EINVAL;
  63         if (keylen > MAX_KEY_SIZE)
  64                 goto inval;
  65         memcpy(evmkey, key, keylen);
  66         evm_initialized |= EVM_INIT_HMAC;
  67         pr_info("key initialized\n");
  68         return 0;
  69 inval:
  70         clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
  71 busy:
  72         pr_err("key initialization failed\n");
  73         return rc;
  74 }
  75 EXPORT_SYMBOL_GPL(evm_set_key);
  76
  77 static struct shash_desc *init_desc(char type, uint8_t hash_algo)
  78 {
  79         long rc;
  80         const char *algo;
  81         struct crypto_shash **tfm;
  82         struct shash_desc *desc;
  83
  84         if (type == EVM_XATTR_HMAC) {
  85                 if (!(evm_initialized & EVM_INIT_HMAC)) {
  86                         pr_err_once("HMAC key is not set\n");
  87                         return ERR_PTR(-ENOKEY);
  88                 }
  89                 tfm = &hmac_tfm;
  90                 algo = evm_hmac;
  91         } else {
  92                 if (hash_algo >= HASH_ALGO__LAST)
  93                         return ERR_PTR(-EINVAL);
  94
  95                 tfm = &evm_tfm[hash_algo];
  96                 algo = hash_algo_name[hash_algo];
  97         }
  98
  99         if (IS_ERR_OR_NULL(*tfm)) {
 100                 mutex_lock(&mutex);
 101                 if (*tfm)
 102                         goto out;
 103                 *tfm = crypto_alloc_shash(algo, 0,
 104                                           CRYPTO_ALG_ASYNC | CRYPTO_NOLOAD);
 105                 if (IS_ERR(*tfm)) {
 106                         rc = PTR_ERR(*tfm);
 107                         pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
 108                         *tfm = NULL;
 109                         mutex_unlock(&mutex);
 110                         return ERR_PTR(rc);
 111                 }
 112                 if (type == EVM_XATTR_HMAC) {
 113                         rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
 114                         if (rc) {
 115                                 crypto_free_shash(*tfm);
 116                                 *tfm = NULL;
 117                                 mutex_unlock(&mutex);
 118                                 return ERR_PTR(rc);
 119                         }
 120                 }
 121 out:
 122                 mutex_unlock(&mutex);
 123         }
 124
 125         desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 126                         GFP_KERNEL);
 127         if (!desc)
 128                 return ERR_PTR(-ENOMEM);
 129
 130         desc->tfm = *tfm;
 131         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 132
 133         rc = crypto_shash_init(desc);
 134         if (rc) {
 135                 kfree(desc);
 136                 return ERR_PTR(rc);
 137         }
 138         return desc;
 139 }
 140
 141 /* Protect against 'cutting & pasting' security.evm xattr, include inode
 142  * specific info.
 143  *
 144  * (Additional directory/file metadata needs to be added for more complete
 145  * protection.)
 146  */
 147 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 148                           char type, char *digest)
 149 {
 150         struct h_misc {
 151                 unsigned long ino;
 152                 __u32 generation;
 153                 uid_t uid;
 154                 gid_t gid;
 155                 umode_t mode;
 156         } hmac_misc;
 157
 158         memset(&hmac_misc, 0, sizeof(hmac_misc));
 159         /* Don't include the inode or generation number in portable
 160          * signatures
 161          */
 162         if (type != EVM_XATTR_PORTABLE_DIGSIG) {
 163                 hmac_misc.ino = inode->i_ino;
 164                 hmac_misc.generation = inode->i_generation;
 165         }
 166         /* The hmac uid and gid must be encoded in the initial user
 167          * namespace (not the filesystems user namespace) as encoding
 168          * them in the filesystems user namespace allows an attack
 169          * where first they are written in an unprivileged fuse mount
 170          * of a filesystem and then the system is tricked to mount the
 171          * filesystem for real on next boot and trust it because
 172          * everything is signed.
 173          */
 174         hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 175         hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 176         hmac_misc.mode = inode->i_mode;
 177         crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 178         if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
 179             type != EVM_XATTR_PORTABLE_DIGSIG)
 180                 crypto_shash_update(desc, &inode->i_sb->s_uuid.b[0],
 181                                     sizeof(inode->i_sb->s_uuid));
 182         crypto_shash_final(desc, digest);
 183 }
 184
 185 /*
 186  * Calculate the HMAC value across the set of protected security xattrs.
 187  *
 188  * Instead of retrieving the requested xattr, for performance, calculate
 189  * the hmac using the requested xattr value. Don't alloc/free memory for
 190  * each xattr, but attempt to re-use the previously allocated memory.
 191  */
 192 static int evm_calc_hmac_or_hash(struct dentry *dentry,
 193                                  const char *req_xattr_name,
 194                                  const char *req_xattr_value,
 195                                  size_t req_xattr_value_len,
 196                                  uint8_t type, struct evm_digest *data)
 197 {
 198         struct inode *inode = d_backing_inode(dentry);
 199         struct xattr_list *xattr;
 200         struct shash_desc *desc;
 201         size_t xattr_size = 0;
 202         char *xattr_value = NULL;
 203         int error;
 204         int size;
 205         bool ima_present = false;
 206
 207         if (!(inode->i_opflags & IOP_XATTR) ||
 208             inode->i_sb->s_user_ns != &init_user_ns)
 209                 return -EOPNOTSUPP;
 210
 211         desc = init_desc(type, data->hdr.algo);
 212         if (IS_ERR(desc))
 213                 return PTR_ERR(desc);
 214
 215         data->hdr.length = crypto_shash_digestsize(desc->tfm);
 216
 217         error = -ENODATA;
 218         list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
 219                 bool is_ima = false;
 220
 221                 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
 222                         is_ima = true;
 223
 224                 if ((req_xattr_name && req_xattr_value)
 225                     && !strcmp(xattr->name, req_xattr_name)) {
 226                         error = 0;
 227                         crypto_shash_update(desc, (const u8 *)req_xattr_value,
 228                                              req_xattr_value_len);
 229                         if (is_ima)
 230                                 ima_present = true;
 231                         continue;
 232                 }
 233                 size = vfs_getxattr_alloc(dentry, xattr->name,
 234                                           &xattr_value, xattr_size, GFP_NOFS);
 235                 if (size == -ENOMEM) {
 236                         error = -ENOMEM;
 237                         goto out;
 238                 }
 239                 if (size < 0)
 240                         continue;
 241
 242                 error = 0;
 243                 xattr_size = size;
 244                 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 245                 if (is_ima)
 246                         ima_present = true;
 247         }
 248         hmac_add_misc(desc, inode, type, data->digest);
 249
 250         /* Portable EVM signatures must include an IMA hash */
 251         if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
 252                 return -EPERM;
 253 out:
 254         kfree(xattr_value);
 255         kfree(desc);
 256         return error;
 257 }
 258
 259 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 260                   const char *req_xattr_value, size_t req_xattr_value_len,
 261                   struct evm_digest *data)
 262 {
 263         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 264                                     req_xattr_value_len, EVM_XATTR_HMAC, data);
 265 }
 266
 267 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 268                   const char *req_xattr_value, size_t req_xattr_value_len,
 269                   char type, struct evm_digest *data)
 270 {
 271         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 272                                      req_xattr_value_len, type, data);
 273 }
 274
 275 static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
 276 {
 277         const struct evm_ima_xattr_data *xattr_data = NULL;
 278         struct integrity_iint_cache *iint;
 279         int rc = 0;
 280
 281         iint = integrity_iint_find(inode);
 282         if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
 283                 return 1;
 284
 285         /* Do this the hard way */
 286         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 287                                 GFP_NOFS);
 288         if (rc <= 0) {
 289                 if (rc == -ENODATA)
 290                         return 0;
 291                 return rc;
 292         }
 293         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
 294                 rc = 1;
 295         else
 296                 rc = 0;
 297
 298         kfree(xattr_data);
 299         return rc;
 300 }
 301
 302
 303 /*
 304  * Calculate the hmac and update security.evm xattr
 305  *
 306  * Expects to be called with i_mutex locked.
 307  */
 308 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 309                         const char *xattr_value, size_t xattr_value_len)
 310 {
 311         struct inode *inode = d_backing_inode(dentry);
 312         struct evm_digest data;
 313         int rc = 0;
 314
 315         /*
 316          * Don't permit any transformation of the EVM xattr if the signature
 317          * is of an immutable type
 318          */
 319         rc = evm_is_immutable(dentry, inode);
 320         if (rc < 0)
 321                 return rc;
 322         if (rc)
 323                 return -EPERM;
 324
 325         data.hdr.algo = HASH_ALGO_SHA1;
 326         rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 327                            xattr_value_len, &data);
 328         if (rc == 0) {
 329                 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
 330                 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 331                                            &data.hdr.xattr.data[1],
 332                                            SHA1_DIGEST_SIZE + 1, 0);
 333         } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 334                 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 335         }
 336         return rc;
 337 }
 338
 339 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 340                   char *hmac_val)
 341 {
 342         struct shash_desc *desc;
 343
 344         desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
 345         if (IS_ERR(desc)) {
 346                 pr_info("init_desc failed\n");
 347                 return PTR_ERR(desc);
 348         }
 349
 350         crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 351         hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
 352         kfree(desc);
 353         return 0;
 354 }
 355
 356 /*
 357  * Get the key from the TPM for the SHA1-HMAC
 358  */
 359 int evm_init_key(void)
 360 {
 361         struct key *evm_key;
 362         struct encrypted_key_payload *ekp;
 363         int rc;
 364
 365         evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 366         if (IS_ERR(evm_key))
 367                 return -ENOENT;
 368
 369         down_read(&evm_key->sem);
 370         ekp = evm_key->payload.data[0];
 371
 372         rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
 373
 374         /* burn the original key contents */
 375         memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 376         up_read(&evm_key->sem);
 377         key_put(evm_key);
 378         return rc;
 379 }