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) "EVM: "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, *tmp_tfm = NULL;
  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;
 118unlock:
 119        mutex_unlock(&mutex);
 120alloc:
 121        desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 122                        GFP_KERNEL);
 123        if (!desc) {
 124                crypto_free_shash(tmp_tfm);
 125                return ERR_PTR(-ENOMEM);
 126        }
 127
 128        desc->tfm = *tfm;
 129
 130        rc = crypto_shash_init(desc);
 131        if (rc) {
 132                crypto_free_shash(tmp_tfm);
 133                kfree(desc);
 134                return ERR_PTR(rc);
 135        }
 136        return desc;
 137}
 138
 139/* Protect against 'cutting & pasting' security.evm xattr, include inode
 140 * specific info.
 141 *
 142 * (Additional directory/file metadata needs to be added for more complete
 143 * protection.)
 144 */
 145static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 146                          char type, char *digest)
 147{
 148        struct h_misc {
 149                unsigned long ino;
 150                __u32 generation;
 151                uid_t uid;
 152                gid_t gid;
 153                umode_t mode;
 154        } hmac_misc;
 155
 156        memset(&hmac_misc, 0, sizeof(hmac_misc));
 157        /* Don't include the inode or generation number in portable
 158         * signatures
 159         */
 160        if (type != EVM_XATTR_PORTABLE_DIGSIG) {
 161                hmac_misc.ino = inode->i_ino;
 162                hmac_misc.generation = inode->i_generation;
 163        }
 164        /* The hmac uid and gid must be encoded in the initial user
 165         * namespace (not the filesystems user namespace) as encoding
 166         * them in the filesystems user namespace allows an attack
 167         * where first they are written in an unprivileged fuse mount
 168         * of a filesystem and then the system is tricked to mount the
 169         * filesystem for real on next boot and trust it because
 170         * everything is signed.
 171         */
 172        hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 173        hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 174        hmac_misc.mode = inode->i_mode;
 175        crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 176        if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
 177            type != EVM_XATTR_PORTABLE_DIGSIG)
 178                crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
 179        crypto_shash_final(desc, digest);
 180
 181        pr_debug("hmac_misc: (%zu) [%*phN]\n", sizeof(struct h_misc),
 182                 (int)sizeof(struct h_misc), &hmac_misc);
 183}
 184
 185/*
 186 * Dump large security xattr values as a continuous ascii hexademical string.
 187 * (pr_debug is limited to 64 bytes.)
 188 */
 189static void dump_security_xattr(const char *prefix, const void *src,
 190                                size_t count)
 191{
 192#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
 193        char *asciihex, *p;
 194
 195        p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL);
 196        if (!asciihex)
 197                return;
 198
 199        p = bin2hex(p, src, count);
 200        *p = 0;
 201        pr_debug("%s: (%zu) %.*s\n", prefix, count, (int)count * 2, asciihex);
 202        kfree(asciihex);
 203#endif
 204}
 205
 206/*
 207 * Calculate the HMAC value across the set of protected security xattrs.
 208 *
 209 * Instead of retrieving the requested xattr, for performance, calculate
 210 * the hmac using the requested xattr value. Don't alloc/free memory for
 211 * each xattr, but attempt to re-use the previously allocated memory.
 212 */
 213static int evm_calc_hmac_or_hash(struct dentry *dentry,
 214                                 const char *req_xattr_name,
 215                                 const char *req_xattr_value,
 216                                 size_t req_xattr_value_len,
 217                                 uint8_t type, struct evm_digest *data)
 218{
 219        struct inode *inode = d_backing_inode(dentry);
 220        struct xattr_list *xattr;
 221        struct shash_desc *desc;
 222        size_t xattr_size = 0;
 223        char *xattr_value = NULL;
 224        int error;
 225        int size, user_space_size;
 226        bool ima_present = false;
 227
 228        if (!(inode->i_opflags & IOP_XATTR) ||
 229            inode->i_sb->s_user_ns != &init_user_ns)
 230                return -EOPNOTSUPP;
 231
 232        desc = init_desc(type, data->hdr.algo);
 233        if (IS_ERR(desc))
 234                return PTR_ERR(desc);
 235
 236        data->hdr.length = crypto_shash_digestsize(desc->tfm);
 237
 238        error = -ENODATA;
 239        list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
 240                bool is_ima = false;
 241
 242                if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
 243                        is_ima = true;
 244
 245                /*
 246                 * Skip non-enabled xattrs for locally calculated
 247                 * signatures/HMACs.
 248                 */
 249                if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled)
 250                        continue;
 251
 252                if ((req_xattr_name && req_xattr_value)
 253                    && !strcmp(xattr->name, req_xattr_name)) {
 254                        error = 0;
 255                        crypto_shash_update(desc, (const u8 *)req_xattr_value,
 256                                             req_xattr_value_len);
 257                        if (is_ima)
 258                                ima_present = true;
 259
 260                        if (req_xattr_value_len < 64)
 261                                pr_debug("%s: (%zu) [%*phN]\n", req_xattr_name,
 262                                         req_xattr_value_len,
 263                                         (int)req_xattr_value_len,
 264                                         req_xattr_value);
 265                        else
 266                                dump_security_xattr(req_xattr_name,
 267                                                    req_xattr_value,
 268                                                    req_xattr_value_len);
 269                        continue;
 270                }
 271                size = vfs_getxattr_alloc(&init_user_ns, dentry, xattr->name,
 272                                          &xattr_value, xattr_size, GFP_NOFS);
 273                if (size == -ENOMEM) {
 274                        error = -ENOMEM;
 275                        goto out;
 276                }
 277                if (size < 0)
 278                        continue;
 279
 280                user_space_size = vfs_getxattr(&init_user_ns, dentry,
 281                                               xattr->name, NULL, 0);
 282                if (user_space_size != size)
 283                        pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n",
 284                                 dentry->d_name.name, xattr->name, size,
 285                                 user_space_size);
 286                error = 0;
 287                xattr_size = size;
 288                crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 289                if (is_ima)
 290                        ima_present = true;
 291
 292                if (xattr_size < 64)
 293                        pr_debug("%s: (%zu) [%*phN]", xattr->name, xattr_size,
 294                                 (int)xattr_size, xattr_value);
 295                else
 296                        dump_security_xattr(xattr->name, xattr_value,
 297                                            xattr_size);
 298        }
 299        hmac_add_misc(desc, inode, type, data->digest);
 300
 301        /* Portable EVM signatures must include an IMA hash */
 302        if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
 303                error = -EPERM;
 304out:
 305        kfree(xattr_value);
 306        kfree(desc);
 307        return error;
 308}
 309
 310int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 311                  const char *req_xattr_value, size_t req_xattr_value_len,
 312                  struct evm_digest *data)
 313{
 314        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 315                                    req_xattr_value_len, EVM_XATTR_HMAC, data);
 316}
 317
 318int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 319                  const char *req_xattr_value, size_t req_xattr_value_len,
 320                  char type, struct evm_digest *data)
 321{
 322        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 323                                     req_xattr_value_len, type, data);
 324}
 325
 326static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
 327{
 328        const struct evm_ima_xattr_data *xattr_data = NULL;
 329        struct integrity_iint_cache *iint;
 330        int rc = 0;
 331
 332        iint = integrity_iint_find(inode);
 333        if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
 334                return 1;
 335
 336        /* Do this the hard way */
 337        rc = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_EVM,
 338                                (char **)&xattr_data, 0, GFP_NOFS);
 339        if (rc <= 0) {
 340                if (rc == -ENODATA)
 341                        return 0;
 342                return rc;
 343        }
 344        if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
 345                rc = 1;
 346        else
 347                rc = 0;
 348
 349        kfree(xattr_data);
 350        return rc;
 351}
 352
 353
 354/*
 355 * Calculate the hmac and update security.evm xattr
 356 *
 357 * Expects to be called with i_mutex locked.
 358 */
 359int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 360                        const char *xattr_value, size_t xattr_value_len)
 361{
 362        struct inode *inode = d_backing_inode(dentry);
 363        struct evm_digest data;
 364        int rc = 0;
 365
 366        /*
 367         * Don't permit any transformation of the EVM xattr if the signature
 368         * is of an immutable type
 369         */
 370        rc = evm_is_immutable(dentry, inode);
 371        if (rc < 0)
 372                return rc;
 373        if (rc)
 374                return -EPERM;
 375
 376        data.hdr.algo = HASH_ALGO_SHA1;
 377        rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 378                           xattr_value_len, &data);
 379        if (rc == 0) {
 380                data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
 381                rc = __vfs_setxattr_noperm(&init_user_ns, dentry,
 382                                           XATTR_NAME_EVM,
 383                                           &data.hdr.xattr.data[1],
 384                                           SHA1_DIGEST_SIZE + 1, 0);
 385        } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 386                rc = __vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_EVM);
 387        }
 388        return rc;
 389}
 390
 391int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 392                  char *hmac_val)
 393{
 394        struct shash_desc *desc;
 395
 396        desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
 397        if (IS_ERR(desc)) {
 398                pr_info("init_desc failed\n");
 399                return PTR_ERR(desc);
 400        }
 401
 402        crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 403        hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
 404        kfree(desc);
 405        return 0;
 406}
 407
 408/*
 409 * Get the key from the TPM for the SHA1-HMAC
 410 */
 411int evm_init_key(void)
 412{
 413        struct key *evm_key;
 414        struct encrypted_key_payload *ekp;
 415        int rc;
 416
 417        evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 418        if (IS_ERR(evm_key))
 419                return -ENOENT;
 420
 421        down_read(&evm_key->sem);
 422        ekp = evm_key->payload.data[0];
 423
 424        rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
 425
 426        /* burn the original key contents */
 427        memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 428        up_read(&evm_key->sem);
 429        key_put(evm_key);
 430        return rc;
 431}
 432