LXR linux/security/integrity/evm/evm

   1/*
   2 * Copyright (C) 2005-2010 IBM Corporation
   3 *
   4 * Authors:
   5 * Mimi Zohar <zohar@us.ibm.com>
   6 * Kylene Hall <kjhall@us.ibm.com>
   7 *
   8 * This program is free software; you can redistribute it and/or modify
   9 * it under the terms of the GNU General Public License as published by
  10 * the Free Software Foundation, version 2 of the License.
  11 *
  12 * File: evm_crypto.c
  13 *       Using root's kernel master key (kmk), calculate the HMAC
  14 */
  15
  16#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  17
  18#include <linux/module.h>
  19#include <linux/crypto.h>
  20#include <linux/xattr.h>
  21#include <linux/evm.h>
  22#include <keys/encrypted-type.h>
  23#include <crypto/hash.h>
  24#include <crypto/hash_info.h>
  25#include "evm.h"
  26
  27#define EVMKEY "evm-key"
  28#define MAX_KEY_SIZE 128
  29static unsigned char evmkey[MAX_KEY_SIZE];
  30static int evmkey_len = MAX_KEY_SIZE;
  31
  32struct crypto_shash *hmac_tfm;
  33static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
  34
  35static DEFINE_MUTEX(mutex);
  36
  37#define EVM_SET_KEY_BUSY 0
  38
  39static unsigned long evm_set_key_flags;
  40
  41static char * const evm_hmac = "hmac(sha1)";
  42
  43/**
  44 * evm_set_key() - set EVM HMAC key from the kernel
  45 * @key: pointer to a buffer with the key data
  46 * @size: length of the key data
  47 *
  48 * This function allows setting the EVM HMAC key from the kernel
  49 * without using the "encrypted" key subsystem keys. It can be used
  50 * by the crypto HW kernel module which has its own way of managing
  51 * keys.
  52 *
  53 * key length should be between 32 and 128 bytes long
  54 */
  55int evm_set_key(void *key, size_t keylen)
  56{
  57        int rc;
  58
  59        rc = -EBUSY;
  60        if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
  61                goto busy;
  62        rc = -EINVAL;
  63        if (keylen > MAX_KEY_SIZE)
  64                goto inval;
  65        memcpy(evmkey, key, keylen);
  66        evm_initialized |= EVM_INIT_HMAC;
  67        pr_info("key initialized\n");
  68        return 0;
  69inval:
  70        clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
  71busy:
  72        pr_err("key initialization failed\n");
  73        return rc;
  74}
  75EXPORT_SYMBOL_GPL(evm_set_key);
  76
  77static struct shash_desc *init_desc(char type, uint8_t hash_algo)
  78{
  79        long rc;
  80        const char *algo;
  81        struct crypto_shash **tfm;
  82        struct shash_desc *desc;
  83
  84        if (type == EVM_XATTR_HMAC) {
  85                if (!(evm_initialized & EVM_INIT_HMAC)) {
  86                        pr_err_once("HMAC key is not set\n");
  87                        return ERR_PTR(-ENOKEY);
  88                }
  89                tfm = &hmac_tfm;
  90                algo = evm_hmac;
  91        } else {
  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,
 101                                          CRYPTO_ALG_ASYNC | CRYPTO_NOLOAD);
 102                if (IS_ERR(*tfm)) {
 103                        rc = PTR_ERR(*tfm);
 104                        pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
 105                        *tfm = NULL;
 106                        mutex_unlock(&mutex);
 107                        return ERR_PTR(rc);
 108                }
 109                if (type == EVM_XATTR_HMAC) {
 110                        rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
 111                        if (rc) {
 112                                crypto_free_shash(*tfm);
 113                                *tfm = NULL;
 114                                mutex_unlock(&mutex);
 115                                return ERR_PTR(rc);
 116                        }
 117                }
 118out:
 119                mutex_unlock(&mutex);
 120        }
 121
 122        desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 123                        GFP_KERNEL);
 124        if (!desc)
 125                return ERR_PTR(-ENOMEM);
 126
 127        desc->tfm = *tfm;
 128        desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 129
 130        rc = crypto_shash_init(desc);
 131        if (rc) {
 132                kfree(desc);
 133                return ERR_PTR(rc);
 134        }
 135        return desc;
 136}
 137
 138/* Protect against 'cutting & pasting' security.evm xattr, include inode
 139 * specific info.
 140 *
 141 * (Additional directory/file metadata needs to be added for more complete
 142 * protection.)
 143 */
 144static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 145                          char type, char *digest)
 146{
 147        struct h_misc {
 148                unsigned long ino;
 149                __u32 generation;
 150                uid_t uid;
 151                gid_t gid;
 152                umode_t mode;
 153        } hmac_misc;
 154
 155        memset(&hmac_misc, 0, sizeof(hmac_misc));
 156        /* Don't include the inode or generation number in portable
 157         * signatures
 158         */
 159        if (type != EVM_XATTR_PORTABLE_DIGSIG) {
 160                hmac_misc.ino = inode->i_ino;
 161                hmac_misc.generation = inode->i_generation;
 162        }
 163        /* The hmac uid and gid must be encoded in the initial user
 164         * namespace (not the filesystems user namespace) as encoding
 165         * them in the filesystems user namespace allows an attack
 166         * where first they are written in an unprivileged fuse mount
 167         * of a filesystem and then the system is tricked to mount the
 168         * filesystem for real on next boot and trust it because
 169         * everything is signed.
 170         */
 171        hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 172        hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 173        hmac_misc.mode = inode->i_mode;
 174        crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 175        if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
 176            type != EVM_XATTR_PORTABLE_DIGSIG)
 177                crypto_shash_update(desc, &inode->i_sb->s_uuid.b[0],
 178                                    sizeof(inode->i_sb->s_uuid));
 179        crypto_shash_final(desc, digest);
 180}
 181
 182/*
 183 * Calculate the HMAC value across the set of protected security xattrs.
 184 *
 185 * Instead of retrieving the requested xattr, for performance, calculate
 186 * the hmac using the requested xattr value. Don't alloc/free memory for
 187 * each xattr, but attempt to re-use the previously allocated memory.
 188 */
 189static int evm_calc_hmac_or_hash(struct dentry *dentry,
 190                                 const char *req_xattr_name,
 191                                 const char *req_xattr_value,
 192                                 size_t req_xattr_value_len,
 193                                 uint8_t type, struct evm_digest *data)
 194{
 195        struct inode *inode = d_backing_inode(dentry);
 196        struct xattr_list *xattr;
 197        struct shash_desc *desc;
 198        size_t xattr_size = 0;
 199        char *xattr_value = NULL;
 200        int error;
 201        int size;
 202        bool ima_present = false;
 203
 204        if (!(inode->i_opflags & IOP_XATTR) ||
 205            inode->i_sb->s_user_ns != &init_user_ns)
 206                return -EOPNOTSUPP;
 207
 208        desc = init_desc(type, data->hdr.algo);
 209        if (IS_ERR(desc))
 210                return PTR_ERR(desc);
 211
 212        data->hdr.length = crypto_shash_digestsize(desc->tfm);
 213
 214        error = -ENODATA;
 215        list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
 216                bool is_ima = false;
 217
 218                if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
 219                        is_ima = true;
 220
 221                if ((req_xattr_name && req_xattr_value)
 222                    && !strcmp(xattr->name, req_xattr_name)) {
 223                        error = 0;
 224                        crypto_shash_update(desc, (const u8 *)req_xattr_value,
 225                                             req_xattr_value_len);
 226                        if (is_ima)
 227                                ima_present = true;
 228                        continue;
 229                }
 230                size = vfs_getxattr_alloc(dentry, xattr->name,
 231                                          &xattr_value, xattr_size, GFP_NOFS);
 232                if (size == -ENOMEM) {
 233                        error = -ENOMEM;
 234                        goto out;
 235                }
 236                if (size < 0)
 237                        continue;
 238
 239                error = 0;
 240                xattr_size = size;
 241                crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 242                if (is_ima)
 243                        ima_present = true;
 244        }
 245        hmac_add_misc(desc, inode, type, data->digest);
 246
 247        /* Portable EVM signatures must include an IMA hash */
 248        if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
 249                return -EPERM;
 250out:
 251        kfree(xattr_value);
 252        kfree(desc);
 253        return error;
 254}
 255
 256int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 257                  const char *req_xattr_value, size_t req_xattr_value_len,
 258                  struct evm_digest *data)
 259{
 260        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 261                                    req_xattr_value_len, EVM_XATTR_HMAC, data);
 262}
 263
 264int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 265                  const char *req_xattr_value, size_t req_xattr_value_len,
 266                  char type, struct evm_digest *data)
 267{
 268        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 269                                     req_xattr_value_len, type, data);
 270}
 271
 272static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
 273{
 274        const struct evm_ima_xattr_data *xattr_data = NULL;
 275        struct integrity_iint_cache *iint;
 276        int rc = 0;
 277
 278        iint = integrity_iint_find(inode);
 279        if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
 280                return 1;
 281
 282        /* Do this the hard way */
 283        rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 284                                GFP_NOFS);
 285        if (rc <= 0) {
 286                if (rc == -ENODATA)
 287                        return 0;
 288                return rc;
 289        }
 290        if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
 291                rc = 1;
 292        else
 293                rc = 0;
 294
 295        kfree(xattr_data);
 296        return rc;
 297}
 298
 299
 300/*
 301 * Calculate the hmac and update security.evm xattr
 302 *
 303 * Expects to be called with i_mutex locked.
 304 */
 305int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 306                        const char *xattr_value, size_t xattr_value_len)
 307{
 308        struct inode *inode = d_backing_inode(dentry);
 309        struct evm_digest data;
 310        int rc = 0;
 311
 312        /*
 313         * Don't permit any transformation of the EVM xattr if the signature
 314         * is of an immutable type
 315         */
 316        rc = evm_is_immutable(dentry, inode);
 317        if (rc < 0)
 318                return rc;
 319        if (rc)
 320                return -EPERM;
 321
 322        data.hdr.algo = HASH_ALGO_SHA1;
 323        rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 324                           xattr_value_len, &data);
 325        if (rc == 0) {
 326                data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
 327                rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 328                                           &data.hdr.xattr.data[1],
 329                                           SHA1_DIGEST_SIZE + 1, 0);
 330        } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 331                rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 332        }
 333        return rc;
 334}
 335
 336int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 337                  char *hmac_val)
 338{
 339        struct shash_desc *desc;
 340
 341        desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
 342        if (IS_ERR(desc)) {
 343                pr_info("init_desc failed\n");
 344                return PTR_ERR(desc);
 345        }
 346
 347        crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 348        hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
 349        kfree(desc);
 350        return 0;
 351}
 352
 353/*
 354 * Get the key from the TPM for the SHA1-HMAC
 355 */
 356int evm_init_key(void)
 357{
 358        struct key *evm_key;
 359        struct encrypted_key_payload *ekp;
 360        int rc;
 361
 362        evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 363        if (IS_ERR(evm_key))
 364                return -ENOENT;
 365
 366        down_read(&evm_key->sem);
 367        ekp = evm_key->payload.data[0];
 368
 369        rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
 370
 371        /* burn the original key contents */
 372        memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 373        up_read(&evm_key->sem);
 374        key_put(evm_key);
 375        return rc;
 376}
 377