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
  40static char * const evm_hmac = "hmac(sha1)";
  41static char * const evm_hash = "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)
  78{
  79        long rc;
  80        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 = &hash_tfm;
  93                algo = evm_hash;
  94        }
  95
  96        if (*tfm == NULL) {
  97                mutex_lock(&mutex);
  98                if (*tfm)
  99                        goto out;
 100                *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
 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        desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 128
 129        rc = crypto_shash_init(desc);
 130        if (rc) {
 131                kfree(desc);
 132                return ERR_PTR(rc);
 133        }
 134        return desc;
 135}
 136
 137/* Protect against 'cutting & pasting' security.evm xattr, include inode
 138 * specific info.
 139 *
 140 * (Additional directory/file metadata needs to be added for more complete
 141 * protection.)
 142 */
 143static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 144                          char type, char *digest)
 145{
 146        struct h_misc {
 147                unsigned long ino;
 148                __u32 generation;
 149                uid_t uid;
 150                gid_t gid;
 151                umode_t mode;
 152        } hmac_misc;
 153
 154        memset(&hmac_misc, 0, sizeof(hmac_misc));
 155        /* Don't include the inode or generation number in portable
 156         * signatures
 157         */
 158        if (type != EVM_XATTR_PORTABLE_DIGSIG) {
 159                hmac_misc.ino = inode->i_ino;
 160                hmac_misc.generation = inode->i_generation;
 161        }
 162        /* The hmac uid and gid must be encoded in the initial user
 163         * namespace (not the filesystems user namespace) as encoding
 164         * them in the filesystems user namespace allows an attack
 165         * where first they are written in an unprivileged fuse mount
 166         * of a filesystem and then the system is tricked to mount the
 167         * filesystem for real on next boot and trust it because
 168         * everything is signed.
 169         */
 170        hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
 171        hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 172        hmac_misc.mode = inode->i_mode;
 173        crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 174        if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
 175            type != EVM_XATTR_PORTABLE_DIGSIG)
 176                crypto_shash_update(desc, &inode->i_sb->s_uuid.b[0],
 177                                    sizeof(inode->i_sb->s_uuid));
 178        crypto_shash_final(desc, digest);
 179}
 180
 181/*
 182 * Calculate the HMAC value across the set of protected security xattrs.
 183 *
 184 * Instead of retrieving the requested xattr, for performance, calculate
 185 * the hmac using the requested xattr value. Don't alloc/free memory for
 186 * each xattr, but attempt to re-use the previously allocated memory.
 187 */
 188static int evm_calc_hmac_or_hash(struct dentry *dentry,
 189                                const char *req_xattr_name,
 190                                const char *req_xattr_value,
 191                                size_t req_xattr_value_len,
 192                                char type, char *digest)
 193{
 194        struct inode *inode = d_backing_inode(dentry);
 195        struct shash_desc *desc;
 196        char **xattrname;
 197        size_t xattr_size = 0;
 198        char *xattr_value = NULL;
 199        int error;
 200        int size;
 201        bool ima_present = false;
 202
 203        if (!(inode->i_opflags & IOP_XATTR))
 204                return -EOPNOTSUPP;
 205
 206        desc = init_desc(type);
 207        if (IS_ERR(desc))
 208                return PTR_ERR(desc);
 209
 210        error = -ENODATA;
 211        for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 212                bool is_ima = false;
 213
 214                if (strcmp(*xattrname, XATTR_NAME_IMA) == 0)
 215                        is_ima = true;
 216
 217                if ((req_xattr_name && req_xattr_value)
 218                    && !strcmp(*xattrname, req_xattr_name)) {
 219                        error = 0;
 220                        crypto_shash_update(desc, (const u8 *)req_xattr_value,
 221                                             req_xattr_value_len);
 222                        if (is_ima)
 223                                ima_present = true;
 224                        continue;
 225                }
 226                size = vfs_getxattr_alloc(dentry, *xattrname,
 227                                          &xattr_value, xattr_size, GFP_NOFS);
 228                if (size == -ENOMEM) {
 229                        error = -ENOMEM;
 230                        goto out;
 231                }
 232                if (size < 0)
 233                        continue;
 234
 235                error = 0;
 236                xattr_size = size;
 237                crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 238                if (is_ima)
 239                        ima_present = true;
 240        }
 241        hmac_add_misc(desc, inode, type, digest);
 242
 243        /* Portable EVM signatures must include an IMA hash */
 244        if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
 245                return -EPERM;
 246out:
 247        kfree(xattr_value);
 248        kfree(desc);
 249        return error;
 250}
 251
 252int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 253                  const char *req_xattr_value, size_t req_xattr_value_len,
 254                  char *digest)
 255{
 256        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 257                               req_xattr_value_len, EVM_XATTR_HMAC, digest);
 258}
 259
 260int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 261                  const char *req_xattr_value, size_t req_xattr_value_len,
 262                  char type, char *digest)
 263{
 264        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
 265                                     req_xattr_value_len, type, digest);
 266}
 267
 268static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
 269{
 270        const struct evm_ima_xattr_data *xattr_data = NULL;
 271        struct integrity_iint_cache *iint;
 272        int rc = 0;
 273
 274        iint = integrity_iint_find(inode);
 275        if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
 276                return 1;
 277
 278        /* Do this the hard way */
 279        rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
 280                                GFP_NOFS);
 281        if (rc <= 0) {
 282                if (rc == -ENODATA)
 283                        return 0;
 284                return rc;
 285        }
 286        if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
 287                rc = 1;
 288        else
 289                rc = 0;
 290
 291        kfree(xattr_data);
 292        return rc;
 293}
 294
 295
 296/*
 297 * Calculate the hmac and update security.evm xattr
 298 *
 299 * Expects to be called with i_mutex locked.
 300 */
 301int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 302                        const char *xattr_value, size_t xattr_value_len)
 303{
 304        struct inode *inode = d_backing_inode(dentry);
 305        struct evm_ima_xattr_data xattr_data;
 306        int rc = 0;
 307
 308        /*
 309         * Don't permit any transformation of the EVM xattr if the signature
 310         * is of an immutable type
 311         */
 312        rc = evm_is_immutable(dentry, inode);
 313        if (rc < 0)
 314                return rc;
 315        if (rc)
 316                return -EPERM;
 317
 318        rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 319                           xattr_value_len, xattr_data.digest);
 320        if (rc == 0) {
 321                xattr_data.type = EVM_XATTR_HMAC;
 322                rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 323                                           &xattr_data,
 324                                           sizeof(xattr_data), 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);
 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