security/integrity/evm/evm_crypto.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2005-2010 IBM Corporation
   4  *
   5  * Authors:
   6  * Mimi Zohar <zohar@us.ibm.com>
   7  * Kylene Hall <kjhall@us.ibm.com>
   8  *
   9  * File: evm_crypto.c
  10  *       Using root's kernel master key (kmk), calculate the HMAC
  11  */
  12
  13 #include <linux/export.h>
  14 #include <linux/crypto.h>
  15 #include <linux/xattr.h>
  16 #include <linux/evm.h>
  17 #include <keys/encrypted-type.h>
  18 #include <crypto/hash.h>
  19 #include <crypto/hash_info.h>
  20 #include "evm.h"
  21
  22 #define EVMKEY "evm-key"
  23 #define MAX_KEY_SIZE 128
  24 static unsigned char evmkey[MAX_KEY_SIZE];
  25 static const int evmkey_len = MAX_KEY_SIZE;
  26
  27 struct crypto_shash *hmac_tfm;
  28 static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
  29
  30 static DEFINE_MUTEX(mutex);
  31
  32 #define EVM_SET_KEY_BUSY 0
  33
  34 static unsigned long evm_set_key_flags;
  35
  36 static const char evm_hmac[] = "hmac(sha1)";
  37
  38 /**
  39  * evm_set_key() - set EVM HMAC key from the kernel
  40  * @key: pointer to a buffer with the key data
  41  * @size: length of the key data
  42  *
  43  * This function allows setting the EVM HMAC key from the kernel
  44  * without using the "encrypted" key subsystem keys. It can be used
  45  * by the crypto HW kernel module which has its own way of managing
  46  * keys.
  47  *
  48  * key length should be between 32 and 128 bytes long
  49  */
  50 int evm_set_key(void *key, size_t keylen)
  51 {
  52         int rc;
  53
  54         rc = -EBUSY;
  55         if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
  56                 goto busy;
  57         rc = -EINVAL;
  58         if (keylen > MAX_KEY_SIZE)
  59                 goto inval;
  60         memcpy(evmkey, key, keylen);
  61         evm_initialized |= EVM_INIT_HMAC;
  62         pr_info("key initialized\n");
  63         return 0;
  64 inval:
  65         clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
  66 busy:
  67         pr_err("key initialization failed\n");
  68         return rc;
  69 }
  70 EXPORT_SYMBOL_GPL(evm_set_key);
  71
  72 static struct shash_desc *init_desc(char type, uint8_t hash_algo)
  73 {
  74         long rc;
  75         const char *algo;
  76         struct crypto_shash **tfm;
  77         struct shash_desc *desc;
  78
  79         if (type == EVM_XATTR_HMAC) {
  80                 if (!(evm_initialized & EVM_INIT_HMAC)) {
  81                         pr_err_once("HMAC key is not set\n");
  82                         return ERR_PTR(-ENOKEY);
  83                 }
  84                 tfm = &hmac_tfm;
  85                 algo = evm_hmac;
  86         } else {
  87                 if (hash_algo >= HASH_ALGO__LAST)
  88                         return ERR_PTR(-EINVAL);
  89
  90                 tfm = &evm_tfm[hash_algo];
  91                 algo = hash_algo_name[hash_algo];
  92         }
  93
  94         if (*tfm == NULL) {
  95                 mutex_lock(&mutex);
  96                 if (*tfm)
  97                         goto out;
  98                 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
  99                 if (IS_ERR(*tfm)) {
 100                         rc = PTR_ERR(*tfm);
 101                         pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
 102                         *tfm = NULL;
 103                         mutex_unlock(&mutex);
 104                         return ERR_PTR(rc);
 105                 }
 106                 if (type == EVM_XATTR_HMAC) {
 107                         rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
 108                         if (rc) {
 109                                 crypto_free_shash(*tfm);
 110                                 *tfm = NULL;
 111                                 mutex_unlock(&mutex);
 112                                 return ERR_PTR(rc);
 113                         }
 114                 }
 115 out:
 116                 mutex_unlock(&mutex);
 117         }
 118
 119         desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 120                         GFP_KERNEL);
 121         if (!desc)
 122                 return ERR_PTR(-ENOMEM);
 123
 124         desc->tfm = *tfm;
 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, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
 174         crypto_shash_final(desc, digest);
 175 }
 176
 177 /*
 178  * Calculate the HMAC value across the set of protected security xattrs.
 179  *
 180  * Instead of retrieving the requested xattr, for performance, calculate
 181  * the hmac using the requested xattr value. Don't alloc/free memory for
 182  * each xattr, but attempt to re-use the previously allocated memory.
 183  */
 184 static int evm_calc_hmac_or_hash(struct dentry *dentry,
 185                                  const char *req_xattr_name,
 186                                  const char *req_xattr_value,
 187                                  size_t req_xattr_value_len,
 188                                  uint8_t type, struct evm_digest *data)
 189 {
 190         struct inode *inode = d_backing_inode(dentry);
 191         struct xattr_list *xattr;
 192         struct shash_desc *desc;
 193         size_t xattr_size = 0;
 194         char *xattr_value = NULL;
 195         int error;
 196         int size;
 197         bool ima_present = false;
 198
 199         if (!(inode->i_opflags & IOP_XATTR) ||
 200             inode->i_sb->s_user_ns != &init_user_ns)
 201                 return -EOPNOTSUPP;
 202
 203         desc = init_desc(type, data->hdr.algo);
 204         if (IS_ERR(desc))
 205                 return PTR_ERR(desc);
 206
 207         data->hdr.length = crypto_shash_digestsize(desc->tfm);
 208
 209         error = -ENODATA;
 210         list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
 211                 bool is_ima = false;
 212
 213                 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
 214                         is_ima = true;
 215
 216                 if ((req_xattr_name && req_xattr_value)
 217                     && !strcmp(xattr->name, req_xattr_name)) {
 218                         error = 0;
 219                         crypto_shash_update(desc, (const u8 *)req_xattr_value,
 220                                              req_xattr_value_len);
 221                         if (is_ima)
 222                                 ima_present = true;
 223                         continue;
 224                 }
 225                 size = vfs_getxattr_alloc(dentry, xattr->name,
 226                                           &xattr_value, xattr_size, GFP_NOFS);
 227                 if (size == -ENOMEM) {
 228                         error = -ENOMEM;
 229                         goto out;
 230                 }
 231                 if (size < 0)
 232                         continue;
 233
 234                 error = 0;
 235                 xattr_size = size;
 236                 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 237                 if (is_ima)
 238                         ima_present = true;
 239         }
 240         hmac_add_misc(desc, inode, type, data->digest);
 241
 242         /* Portable EVM signatures must include an IMA hash */
 243         if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
 244                 return -EPERM;
 245 out:
 246         kfree(xattr_value);
 247         kfree(desc);
 248         return error;
 249 }
 250
 251 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 252                   const char *req_xattr_value, size_t req_xattr_value_len,
 253                   struct evm_digest *data)
 254 {
 255         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 256                                     req_xattr_value_len, EVM_XATTR_HMAC, data);
 257 }
 258
 259 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 260                   const char *req_xattr_value, size_t req_xattr_value_len,
 261                   char type, struct evm_digest *data)
 262 {
 263         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 264                                      req_xattr_value_len, type, data);
 265 }
 266
 267 static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
 268 {
 269         const struct evm_ima_xattr_data *xattr_data = NULL;
 270         struct integrity_iint_cache *iint;
 271         int rc = 0;
 272
 273         iint = integrity_iint_find(inode);
 274         if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
 275                 return 1;
 276
 277         /* Do this the hard way */
 278         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 279                                 GFP_NOFS);
 280         if (rc <= 0) {
 281                 if (rc == -ENODATA)
 282                         return 0;
 283                 return rc;
 284         }
 285         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
 286                 rc = 1;
 287         else
 288                 rc = 0;
 289
 290         kfree(xattr_data);
 291         return rc;
 292 }
 293
 294
 295 /*
 296  * Calculate the hmac and update security.evm xattr
 297  *
 298  * Expects to be called with i_mutex locked.
 299  */
 300 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 301                         const char *xattr_value, size_t xattr_value_len)
 302 {
 303         struct inode *inode = d_backing_inode(dentry);
 304         struct evm_digest data;
 305         int rc = 0;
 306
 307         /*
 308          * Don't permit any transformation of the EVM xattr if the signature
 309          * is of an immutable type
 310          */
 311         rc = evm_is_immutable(dentry, inode);
 312         if (rc < 0)
 313                 return rc;
 314         if (rc)
 315                 return -EPERM;
 316
 317         data.hdr.algo = HASH_ALGO_SHA1;
 318         rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 319                            xattr_value_len, &data);
 320         if (rc == 0) {
 321                 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
 322                 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 323                                            &data.hdr.xattr.data[1],
 324                                            SHA1_DIGEST_SIZE + 1, 0);
 325         } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 326                 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 327         }
 328         return rc;
 329 }
 330
 331 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 332                   char *hmac_val)
 333 {
 334         struct shash_desc *desc;
 335
 336         desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
 337         if (IS_ERR(desc)) {
 338                 pr_info("init_desc failed\n");
 339                 return PTR_ERR(desc);
 340         }
 341
 342         crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 343         hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
 344         kfree(desc);
 345         return 0;
 346 }
 347
 348 /*
 349  * Get the key from the TPM for the SHA1-HMAC
 350  */
 351 int evm_init_key(void)
 352 {
 353         struct key *evm_key;
 354         struct encrypted_key_payload *ekp;
 355         int rc;
 356
 357         evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 358         if (IS_ERR(evm_key))
 359                 return -ENOENT;
 360
 361         down_read(&evm_key->sem);
 362         ekp = evm_key->payload.data[0];
 363
 364         rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
 365
 366         /* burn the original key contents */
 367         memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 368         up_read(&evm_key->sem);
 369         key_put(evm_key);
 370         return rc;
 371 }