root/security/integrity/evm/evm_crypto.c

DEFINITIONS

1. evm_set_key
2. init_desc
3. hmac_add_misc
4. evm_calc_hmac_or_hash
5. evm_calc_hmac
6. evm_calc_hash
7. evm_is_immutable
8. evm_update_evmxattr
9. evm_init_hmac
10. evm_init_key

   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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  14 
  15 #include <linux/export.h>
  16 #include <linux/crypto.h>
  17 #include <linux/xattr.h>
  18 #include <linux/evm.h>
  19 #include <keys/encrypted-type.h>
  20 #include <crypto/hash.h>
  21 #include <crypto/hash_info.h>
  22 #include "evm.h"
  23 
  24 #define EVMKEY "evm-key"
  25 #define MAX_KEY_SIZE 128
  26 static unsigned char evmkey[MAX_KEY_SIZE];
  27 static const int evmkey_len = MAX_KEY_SIZE;
  28 
  29 struct crypto_shash *hmac_tfm;
  30 static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
  31 
  32 static DEFINE_MUTEX(mutex);
  33 
  34 #define EVM_SET_KEY_BUSY 0
  35 
  36 static unsigned long evm_set_key_flags;
  37 
  38 static const char evm_hmac[] = "hmac(sha1)";
  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, uint8_t hash_algo)
  75 {
  76         long rc;
  77         const char *algo;
  78         struct crypto_shash **tfm, *tmp_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                 if (hash_algo >= HASH_ALGO__LAST)
  90                         return ERR_PTR(-EINVAL);
  91 
  92                 tfm = &evm_tfm[hash_algo];
  93                 algo = hash_algo_name[hash_algo];
  94         }
  95 
  96         if (*tfm)
  97                 goto alloc;
  98         mutex_lock(&mutex);
  99         if (*tfm)
 100                 goto unlock;
 101 
 102         tmp_tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
 103         if (IS_ERR(tmp_tfm)) {
 104                 pr_err("Can not allocate %s (reason: %ld)\n", algo,
 105                        PTR_ERR(tmp_tfm));
 106                 mutex_unlock(&mutex);
 107                 return ERR_CAST(tmp_tfm);
 108         }
 109         if (type == EVM_XATTR_HMAC) {
 110                 rc = crypto_shash_setkey(tmp_tfm, evmkey, evmkey_len);
 111                 if (rc) {
 112                         crypto_free_shash(tmp_tfm);
 113                         mutex_unlock(&mutex);
 114                         return ERR_PTR(rc);
 115                 }
 116         }
 117         *tfm = tmp_tfm;
 118 unlock:
 119         mutex_unlock(&mutex);
 120 alloc:
 121         desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 122                         GFP_KERNEL);
 123         if (!desc)
 124                 return ERR_PTR(-ENOMEM);
 125 
 126         desc->tfm = *tfm;
 127 
 128         rc = crypto_shash_init(desc);
 129         if (rc) {
 130                 kfree(desc);
 131                 return ERR_PTR(rc);
 132         }
 133         return desc;
 134 }
 135 
 136 /* Protect against 'cutting & pasting' security.evm xattr, include inode
 137  * specific info.
 138  *
 139  * (Additional directory/file metadata needs to be added for more complete
 140  * protection.)
 141  */
 142 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 143                           char type, char *digest)
 144 {
 145         struct h_misc {
 146                 unsigned long ino;
 147                 __u32 generation;
 148                 uid_t uid;
 149                 gid_t gid;
 150                 umode_t mode;
 151         } hmac_misc;
 152 
 153         memset(&hmac_misc, 0, sizeof(hmac_misc));
 154         /* Don't include the inode or generation number in portable
 155          * signatures
 156          */
 157         if (type != EVM_XATTR_PORTABLE_DIGSIG) {
 158                 hmac_misc.ino = inode->i_ino;
 159                 hmac_misc.generation = inode->i_generation;
 160         }
 161         /* The hmac uid and gid must be encoded in the initial user
 162          * namespace (not the filesystems user namespace) as encoding
 163          * them in the filesystems user namespace allows an attack
 164          * where first they are written in an unprivileged fuse mount
 165          * of a filesystem and then the system is tricked to mount the
 166          * filesystem for real on next boot and trust it because
 167          * everything is signed.
 168          */
 169         hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 170         hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 171         hmac_misc.mode = inode->i_mode;
 172         crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 173         if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
 174             type != EVM_XATTR_PORTABLE_DIGSIG)
 175                 crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
 176         crypto_shash_final(desc, digest);
 177 }
 178 
 179 /*
 180  * Calculate the HMAC value across the set of protected security xattrs.
 181  *
 182  * Instead of retrieving the requested xattr, for performance, calculate
 183  * the hmac using the requested xattr value. Don't alloc/free memory for
 184  * each xattr, but attempt to re-use the previously allocated memory.
 185  */
 186 static int evm_calc_hmac_or_hash(struct dentry *dentry,
 187                                  const char *req_xattr_name,
 188                                  const char *req_xattr_value,
 189                                  size_t req_xattr_value_len,
 190                                  uint8_t type, struct evm_digest *data)
 191 {
 192         struct inode *inode = d_backing_inode(dentry);
 193         struct xattr_list *xattr;
 194         struct shash_desc *desc;
 195         size_t xattr_size = 0;
 196         char *xattr_value = NULL;
 197         int error;
 198         int size;
 199         bool ima_present = false;
 200 
 201         if (!(inode->i_opflags & IOP_XATTR) ||
 202             inode->i_sb->s_user_ns != &init_user_ns)
 203                 return -EOPNOTSUPP;
 204 
 205         desc = init_desc(type, data->hdr.algo);
 206         if (IS_ERR(desc))
 207                 return PTR_ERR(desc);
 208 
 209         data->hdr.length = crypto_shash_digestsize(desc->tfm);
 210 
 211         error = -ENODATA;
 212         list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
 213                 bool is_ima = false;
 214 
 215                 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
 216                         is_ima = true;
 217 
 218                 if ((req_xattr_name && req_xattr_value)
 219                     && !strcmp(xattr->name, req_xattr_name)) {
 220                         error = 0;
 221                         crypto_shash_update(desc, (const u8 *)req_xattr_value,
 222                                              req_xattr_value_len);
 223                         if (is_ima)
 224                                 ima_present = true;
 225                         continue;
 226                 }
 227                 size = vfs_getxattr_alloc(dentry, xattr->name,
 228                                           &xattr_value, xattr_size, GFP_NOFS);
 229                 if (size == -ENOMEM) {
 230                         error = -ENOMEM;
 231                         goto out;
 232                 }
 233                 if (size < 0)
 234                         continue;
 235 
 236                 error = 0;
 237                 xattr_size = size;
 238                 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 239                 if (is_ima)
 240                         ima_present = true;
 241         }
 242         hmac_add_misc(desc, inode, type, data->digest);
 243 
 244         /* Portable EVM signatures must include an IMA hash */
 245         if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
 246                 return -EPERM;
 247 out:
 248         kfree(xattr_value);
 249         kfree(desc);
 250         return error;
 251 }
 252 
 253 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 254                   const char *req_xattr_value, size_t req_xattr_value_len,
 255                   struct evm_digest *data)
 256 {
 257         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 258                                     req_xattr_value_len, EVM_XATTR_HMAC, data);
 259 }
 260 
 261 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 262                   const char *req_xattr_value, size_t req_xattr_value_len,
 263                   char type, struct evm_digest *data)
 264 {
 265         return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 266                                      req_xattr_value_len, type, data);
 267 }
 268 
 269 static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
 270 {
 271         const struct evm_ima_xattr_data *xattr_data = NULL;
 272         struct integrity_iint_cache *iint;
 273         int rc = 0;
 274 
 275         iint = integrity_iint_find(inode);
 276         if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
 277                 return 1;
 278 
 279         /* Do this the hard way */
 280         rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 281                                 GFP_NOFS);
 282         if (rc <= 0) {
 283                 if (rc == -ENODATA)
 284                         return 0;
 285                 return rc;
 286         }
 287         if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
 288                 rc = 1;
 289         else
 290                 rc = 0;
 291 
 292         kfree(xattr_data);
 293         return rc;
 294 }
 295 
 296 
 297 /*
 298  * Calculate the hmac and update security.evm xattr
 299  *
 300  * Expects to be called with i_mutex locked.
 301  */
 302 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 303                         const char *xattr_value, size_t xattr_value_len)
 304 {
 305         struct inode *inode = d_backing_inode(dentry);
 306         struct evm_digest data;
 307         int rc = 0;
 308 
 309         /*
 310          * Don't permit any transformation of the EVM xattr if the signature
 311          * is of an immutable type
 312          */
 313         rc = evm_is_immutable(dentry, inode);
 314         if (rc < 0)
 315                 return rc;
 316         if (rc)
 317                 return -EPERM;
 318 
 319         data.hdr.algo = HASH_ALGO_SHA1;
 320         rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 321                            xattr_value_len, &data);
 322         if (rc == 0) {
 323                 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
 324                 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 325                                            &data.hdr.xattr.data[1],
 326                                            SHA1_DIGEST_SIZE + 1, 0);
 327         } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 328                 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 329         }
 330         return rc;
 331 }
 332 
 333 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 334                   char *hmac_val)
 335 {
 336         struct shash_desc *desc;
 337 
 338         desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
 339         if (IS_ERR(desc)) {
 340                 pr_info("init_desc failed\n");
 341                 return PTR_ERR(desc);
 342         }
 343 
 344         crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 345         hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
 346         kfree(desc);
 347         return 0;
 348 }
 349 
 350 /*
 351  * Get the key from the TPM for the SHA1-HMAC
 352  */
 353 int evm_init_key(void)
 354 {
 355         struct key *evm_key;
 356         struct encrypted_key_payload *ekp;
 357         int rc;
 358 
 359         evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 360         if (IS_ERR(evm_key))
 361                 return -ENOENT;
 362 
 363         down_read(&evm_key->sem);
 364         ekp = evm_key->payload.data[0];
 365 
 366         rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
 367 
 368         /* burn the original key contents */
 369         memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 370         up_read(&evm_key->sem);
 371         key_put(evm_key);
 372         return rc;
 373 }