LXR linux/security/integrity/evm/evm

   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
  24static unsigned char evmkey[MAX_KEY_SIZE];
  25static const int evmkey_len = MAX_KEY_SIZE;
  26
  27struct crypto_shash *hmac_tfm;
  28static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
  29
  30static DEFINE_MUTEX(mutex);
  31
  32#define EVM_SET_KEY_BUSY 0
  33
  34static unsigned long evm_set_key_flags;
  35
  36static 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 */
  50int 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;
  64inval:
  65        clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
  66busy:
  67        pr_err("key initialization failed\n");
  68        return rc;
  69}
  70EXPORT_SYMBOL_GPL(evm_set_key);
  71
  72static 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;
  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;
 116unlock:
 117        mutex_unlock(&mutex);
 118alloc:
 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 */
 140static 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 */
 184static 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_lockless(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                error = -EPERM;
 245out:
 246        kfree(xattr_value);
 247        kfree(desc);
 248        return error;
 249}
 250
 251int 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
 259int 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
 267static 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 */
 300int 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
 331int 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 */
 351int 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}
 372