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 /* 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 */ 179 static 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); 223 224 out: 225 kfree(xattr_value); 226 kfree(desc); 227 return error; 228 } 229 230 int 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 } 237 238 int 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 */ 251 int 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 } 270 271 int 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 */ 291 int 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