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 "evm.h"
  25
  26#define EVMKEY "evm-key"
  27#define MAX_KEY_SIZE 128
  28static unsigned char evmkey[MAX_KEY_SIZE];
  29static int evmkey_len = MAX_KEY_SIZE;
  30
  31struct crypto_shash *hmac_tfm;
  32struct crypto_shash *hash_tfm;
  33
  34static DEFINE_MUTEX(mutex);
  35
  36#define EVM_SET_KEY_BUSY 0
  37
  38static unsigned long evm_set_key_flags;
  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)
  75{
  76        long rc;
  77        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("HMAC key is not set\n");
  84                        return ERR_PTR(-ENOKEY);
  85                }
  86                tfm = &hmac_tfm;
  87                algo = evm_hmac;
  88        } else {
  89                tfm = &hash_tfm;
  90                algo = evm_hash;
  91        }
  92
  93        if (*tfm == NULL) {
  94                mutex_lock(&mutex);
  95                if (*tfm)
  96                        goto out;
  97                *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
  98                if (IS_ERR(*tfm)) {
  99                        rc = PTR_ERR(*tfm);
 100                        pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
 101                        *tfm = NULL;
 102                        mutex_unlock(&mutex);
 103                        return ERR_PTR(rc);
 104                }
 105                if (type == EVM_XATTR_HMAC) {
 106                        rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
 107                        if (rc) {
 108                                crypto_free_shash(*tfm);
 109                                *tfm = NULL;
 110                                mutex_unlock(&mutex);
 111                                return ERR_PTR(rc);
 112                        }
 113                }
 114out:
 115                mutex_unlock(&mutex);
 116        }
 117
 118        desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 119                        GFP_KERNEL);
 120        if (!desc)
 121                return ERR_PTR(-ENOMEM);
 122
 123        desc->tfm = *tfm;
 124        desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 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 *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        hmac_misc.ino = inode->i_ino;
 153        hmac_misc.generation = inode->i_generation;
 154        /* The hmac uid and gid must be encoded in the initial user
 155         * namespace (not the filesystems user namespace) as encoding
 156         * them in the filesystems user namespace allows an attack
 157         * where first they are written in an unprivileged fuse mount
 158         * of a filesystem and then the system is tricked to mount the
 159         * filesystem for real on next boot and trust it because
 160         * everything is signed.
 161         */
 162        hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 163        hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 164        hmac_misc.mode = inode->i_mode;
 165        crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 166        if (evm_hmac_attrs & EVM_ATTR_FSUUID)
 167                crypto_shash_update(desc, &inode->i_sb->s_uuid.b[0],
 168                                    sizeof(inode->i_sb->s_uuid));
 169        crypto_shash_final(desc, digest);
 170}
 171
 172/*
 173 * Calculate the HMAC value across the set of protected security xattrs.
 174 *
 175 * Instead of retrieving the requested xattr, for performance, calculate
 176 * the hmac using the requested xattr value. Don't alloc/free memory for
 177 * each xattr, but attempt to re-use the previously allocated memory.
 178 */
 179static int evm_calc_hmac_or_hash(struct dentry *dentry,
 180                                const char *req_xattr_name,
 181                                const char *req_xattr_value,
 182                                size_t req_xattr_value_len,
 183                                char type, char *digest)
 184{
 185        struct inode *inode = d_backing_inode(dentry);
 186        struct shash_desc *desc;
 187        char **xattrname;
 188        size_t xattr_size = 0;
 189        char *xattr_value = NULL;
 190        int error;
 191        int size;
 192
 193        if (!(inode->i_opflags & IOP_XATTR))
 194                return -EOPNOTSUPP;
 195
 196        desc = init_desc(type);
 197        if (IS_ERR(desc))
 198                return PTR_ERR(desc);
 199
 200        error = -ENODATA;
 201        for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 202                if ((req_xattr_name && req_xattr_value)
 203                    && !strcmp(*xattrname, req_xattr_name)) {
 204                        error = 0;
 205                        crypto_shash_update(desc, (const u8 *)req_xattr_value,
 206                                             req_xattr_value_len);
 207                        continue;
 208                }
 209                size = vfs_getxattr_alloc(dentry, *xattrname,
 210                                          &xattr_value, xattr_size, GFP_NOFS);
 211                if (size == -ENOMEM) {
 212                        error = -ENOMEM;
 213                        goto out;
 214                }
 215                if (size < 0)
 216                        continue;
 217
 218                error = 0;
 219                xattr_size = size;
 220                crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 221        }
 222        hmac_add_misc(desc, inode, digest);
 223
 224out:
 225        kfree(xattr_value);
 226        kfree(desc);
 227        return error;
 228}
 229
 230int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 231                  const char *req_xattr_value, size_t req_xattr_value_len,
 232                  char *digest)
 233{
 234        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 235                                req_xattr_value_len, EVM_XATTR_HMAC, digest);
 236}
 237
 238int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 239                  const char *req_xattr_value, size_t req_xattr_value_len,
 240                  char *digest)
 241{
 242        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 243                                req_xattr_value_len, IMA_XATTR_DIGEST, digest);
 244}
 245
 246/*
 247 * Calculate the hmac and update security.evm xattr
 248 *
 249 * Expects to be called with i_mutex locked.
 250 */
 251int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 252                        const char *xattr_value, size_t xattr_value_len)
 253{
 254        struct inode *inode = d_backing_inode(dentry);
 255        struct evm_ima_xattr_data xattr_data;
 256        int rc = 0;
 257
 258        rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 259                           xattr_value_len, xattr_data.digest);
 260        if (rc == 0) {
 261                xattr_data.type = EVM_XATTR_HMAC;
 262                rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 263                                           &xattr_data,
 264                                           sizeof(xattr_data), 0);
 265        } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 266                rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 267        }
 268        return rc;
 269}
 270
 271int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 272                  char *hmac_val)
 273{
 274        struct shash_desc *desc;
 275
 276        desc = init_desc(EVM_XATTR_HMAC);
 277        if (IS_ERR(desc)) {
 278                pr_info("init_desc failed\n");
 279                return PTR_ERR(desc);
 280        }
 281
 282        crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
 283        hmac_add_misc(desc, inode, hmac_val);
 284        kfree(desc);
 285        return 0;
 286}
 287
 288/*
 289 * Get the key from the TPM for the SHA1-HMAC
 290 */
 291int evm_init_key(void)
 292{
 293        struct key *evm_key;
 294        struct encrypted_key_payload *ekp;
 295        int rc;
 296
 297        evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
 298        if (IS_ERR(evm_key))
 299                return -ENOENT;
 300
 301        down_read(&evm_key->sem);
 302        ekp = evm_key->payload.data[0];
 303
 304        rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
 305
 306        /* burn the original key contents */
 307        memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
 308        up_read(&evm_key->sem);
 309        key_put(evm_key);
 310        return rc;
 311}
 312