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