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#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
  26static unsigned char evmkey[MAX_KEY_SIZE];
  27static const int evmkey_len = MAX_KEY_SIZE;
  28
  29struct crypto_shash *hmac_tfm;
  30static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
  31
  32static DEFINE_MUTEX(mutex);
  33
  34#define EVM_SET_KEY_BUSY 0
  35
  36static unsigned long evm_set_key_flags;
  37
  38static 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 */
  52int 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;
  66inval:
  67        clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
  68busy:
  69        pr_err("key initialization failed\n");
  70        return rc;
  71}
  72EXPORT_SYMBOL_GPL(evm_set_key);
  73
  74static struct shash_desc *init_desc(char type, uint8_t hash_algo)
  75{
  76        long rc;
  77        const char *algo;
  78        struct crypto_shash **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 == NULL) {
  97                mutex_lock(&mutex);
  98                if (*tfm)
  99                        goto out;
 100                *tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
 101                if (IS_ERR(*tfm)) {
 102                        rc = PTR_ERR(*tfm);
 103                        pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
 104                        *tfm = NULL;
 105                        mutex_unlock(&mutex);
 106                        return ERR_PTR(rc);
 107                }
 108                if (type == EVM_XATTR_HMAC) {
 109                        rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
 110                        if (rc) {
 111                                crypto_free_shash(*tfm);
 112                                *tfm = NULL;
 113                                mutex_unlock(&mutex);
 114                                return ERR_PTR(rc);
 115                        }
 116                }
 117out:
 118                mutex_unlock(&mutex);
 119        }
 120
 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 */
 142static 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 */
 186static 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_rcu(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;
 247out:
 248        kfree(xattr_value);
 249        kfree(desc);
 250        return error;
 251}
 252
 253int 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
 261int 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
 269static 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 */
 302int 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
 333int 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 */
 353int 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}
 374