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 28 static unsigned char evmkey[MAX_KEY_SIZE]; 29 static int evmkey_len = MAX_KEY_SIZE; 30 31 struct crypto_shash *hmac_tfm; 32 struct crypto_shash *hash_tfm; 33 34 static DEFINE_MUTEX(mutex); 35 36 #define EVM_SET_KEY_BUSY 0 37 38 static 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 */ 52 int 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; 66 inval: 67 clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags); 68 busy: 69 pr_err("key initialization failed\n"); 70 return rc; 71 } 72 EXPORT_SYMBOL_GPL(evm_set_key); 73 74 static 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 } 114 out: 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 */ 140 static 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 hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid); 155 hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid); 156 hmac_misc.mode = inode->i_mode; 157 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc)); 158 if (evm_hmac_attrs & EVM_ATTR_FSUUID) 159 crypto_shash_update(desc, inode->i_sb->s_uuid, 160 sizeof(inode->i_sb->s_uuid)); 161 crypto_shash_final(desc, digest); 162 } 163 164 /* 165 * Calculate the HMAC value across the set of protected security xattrs. 166 * 167 * Instead of retrieving the requested xattr, for performance, calculate 168 * the hmac using the requested xattr value. Don't alloc/free memory for 169 * each xattr, but attempt to re-use the previously allocated memory. 170 */ 171 static int evm_calc_hmac_or_hash(struct dentry *dentry, 172 const char *req_xattr_name, 173 const char *req_xattr_value, 174 size_t req_xattr_value_len, 175 char type, char *digest) 176 { 177 struct inode *inode = d_backing_inode(dentry); 178 struct shash_desc *desc; 179 char **xattrname; 180 size_t xattr_size = 0; 181 char *xattr_value = NULL; 182 int error; 183 int size; 184 185 if (!inode->i_op->getxattr) 186 return -EOPNOTSUPP; 187 desc = init_desc(type); 188 if (IS_ERR(desc)) 189 return PTR_ERR(desc); 190 191 error = -ENODATA; 192 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) { 193 if ((req_xattr_name && req_xattr_value) 194 && !strcmp(*xattrname, req_xattr_name)) { 195 error = 0; 196 crypto_shash_update(desc, (const u8 *)req_xattr_value, 197 req_xattr_value_len); 198 continue; 199 } 200 size = vfs_getxattr_alloc(dentry, *xattrname, 201 &xattr_value, xattr_size, GFP_NOFS); 202 if (size == -ENOMEM) { 203 error = -ENOMEM; 204 goto out; 205 } 206 if (size < 0) 207 continue; 208 209 error = 0; 210 xattr_size = size; 211 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 212 } 213 hmac_add_misc(desc, inode, digest); 214 215 out: 216 kfree(xattr_value); 217 kfree(desc); 218 return error; 219 } 220 221 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 222 const char *req_xattr_value, size_t req_xattr_value_len, 223 char *digest) 224 { 225 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 226 req_xattr_value_len, EVM_XATTR_HMAC, digest); 227 } 228 229 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 230 const char *req_xattr_value, size_t req_xattr_value_len, 231 char *digest) 232 { 233 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 234 req_xattr_value_len, IMA_XATTR_DIGEST, digest); 235 } 236 237 /* 238 * Calculate the hmac and update security.evm xattr 239 * 240 * Expects to be called with i_mutex locked. 241 */ 242 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 243 const char *xattr_value, size_t xattr_value_len) 244 { 245 struct inode *inode = d_backing_inode(dentry); 246 struct evm_ima_xattr_data xattr_data; 247 int rc = 0; 248 249 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 250 xattr_value_len, xattr_data.digest); 251 if (rc == 0) { 252 xattr_data.type = EVM_XATTR_HMAC; 253 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM, 254 &xattr_data, 255 sizeof(xattr_data), 0); 256 } else if (rc == -ENODATA && inode->i_op->removexattr) { 257 rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM); 258 } 259 return rc; 260 } 261 262 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, 263 char *hmac_val) 264 { 265 struct shash_desc *desc; 266 267 desc = init_desc(EVM_XATTR_HMAC); 268 if (IS_ERR(desc)) { 269 pr_info("init_desc failed\n"); 270 return PTR_ERR(desc); 271 } 272 273 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); 274 hmac_add_misc(desc, inode, hmac_val); 275 kfree(desc); 276 return 0; 277 } 278 279 /* 280 * Get the key from the TPM for the SHA1-HMAC 281 */ 282 int evm_init_key(void) 283 { 284 struct key *evm_key; 285 struct encrypted_key_payload *ekp; 286 int rc; 287 288 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 289 if (IS_ERR(evm_key)) 290 return -ENOENT; 291 292 down_read(&evm_key->sem); 293 ekp = evm_key->payload.data[0]; 294 295 rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen); 296 297 /* burn the original key contents */ 298 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 299 up_read(&evm_key->sem); 300 key_put(evm_key); 301 return rc; 302 } 303