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