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 #include <linux/module.h> 17 #include <linux/crypto.h> 18 #include <linux/xattr.h> 19 #include <keys/encrypted-type.h> 20 #include <crypto/hash.h> 21 #include "evm.h" 22 23 #define EVMKEY "evm-key" 24 #define MAX_KEY_SIZE 128 25 static unsigned char evmkey[MAX_KEY_SIZE]; 26 static int evmkey_len = MAX_KEY_SIZE; 27 28 struct crypto_shash *hmac_tfm; 29 struct crypto_shash *hash_tfm; 30 31 static DEFINE_MUTEX(mutex); 32 33 static struct shash_desc *init_desc(char type) 34 { 35 long rc; 36 char *algo; 37 struct crypto_shash **tfm; 38 struct shash_desc *desc; 39 40 if (type == EVM_XATTR_HMAC) { 41 tfm = &hmac_tfm; 42 algo = evm_hmac; 43 } else { 44 tfm = &hash_tfm; 45 algo = evm_hash; 46 } 47 48 if (*tfm == NULL) { 49 mutex_lock(&mutex); 50 if (*tfm) 51 goto out; 52 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC); 53 if (IS_ERR(*tfm)) { 54 rc = PTR_ERR(*tfm); 55 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc); 56 *tfm = NULL; 57 mutex_unlock(&mutex); 58 return ERR_PTR(rc); 59 } 60 if (type == EVM_XATTR_HMAC) { 61 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len); 62 if (rc) { 63 crypto_free_shash(*tfm); 64 *tfm = NULL; 65 mutex_unlock(&mutex); 66 return ERR_PTR(rc); 67 } 68 } 69 out: 70 mutex_unlock(&mutex); 71 } 72 73 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm), 74 GFP_KERNEL); 75 if (!desc) 76 return ERR_PTR(-ENOMEM); 77 78 desc->tfm = *tfm; 79 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; 80 81 rc = crypto_shash_init(desc); 82 if (rc) { 83 kfree(desc); 84 return ERR_PTR(rc); 85 } 86 return desc; 87 } 88 89 /* Protect against 'cutting & pasting' security.evm xattr, include inode 90 * specific info. 91 * 92 * (Additional directory/file metadata needs to be added for more complete 93 * protection.) 94 */ 95 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode, 96 char *digest) 97 { 98 struct h_misc { 99 unsigned long ino; 100 __u32 generation; 101 uid_t uid; 102 gid_t gid; 103 umode_t mode; 104 } hmac_misc; 105 106 memset(&hmac_misc, 0, sizeof hmac_misc); 107 hmac_misc.ino = inode->i_ino; 108 hmac_misc.generation = inode->i_generation; 109 hmac_misc.uid = inode->i_uid; 110 hmac_misc.gid = inode->i_gid; 111 hmac_misc.mode = inode->i_mode; 112 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof hmac_misc); 113 crypto_shash_final(desc, digest); 114 } 115 116 /* 117 * Calculate the HMAC value across the set of protected security xattrs. 118 * 119 * Instead of retrieving the requested xattr, for performance, calculate 120 * the hmac using the requested xattr value. Don't alloc/free memory for 121 * each xattr, but attempt to re-use the previously allocated memory. 122 */ 123 static int evm_calc_hmac_or_hash(struct dentry *dentry, 124 const char *req_xattr_name, 125 const char *req_xattr_value, 126 size_t req_xattr_value_len, 127 char type, char *digest) 128 { 129 struct inode *inode = dentry->d_inode; 130 struct shash_desc *desc; 131 char **xattrname; 132 size_t xattr_size = 0; 133 char *xattr_value = NULL; 134 int error; 135 int size; 136 137 if (!inode->i_op || !inode->i_op->getxattr) 138 return -EOPNOTSUPP; 139 desc = init_desc(type); 140 if (IS_ERR(desc)) 141 return PTR_ERR(desc); 142 143 error = -ENODATA; 144 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) { 145 if ((req_xattr_name && req_xattr_value) 146 && !strcmp(*xattrname, req_xattr_name)) { 147 error = 0; 148 crypto_shash_update(desc, (const u8 *)req_xattr_value, 149 req_xattr_value_len); 150 continue; 151 } 152 size = vfs_getxattr_alloc(dentry, *xattrname, 153 &xattr_value, xattr_size, GFP_NOFS); 154 if (size == -ENOMEM) { 155 error = -ENOMEM; 156 goto out; 157 } 158 if (size < 0) 159 continue; 160 161 error = 0; 162 xattr_size = size; 163 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 164 } 165 hmac_add_misc(desc, inode, digest); 166 167 out: 168 kfree(xattr_value); 169 kfree(desc); 170 return error; 171 } 172 173 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 174 const char *req_xattr_value, size_t req_xattr_value_len, 175 char *digest) 176 { 177 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 178 req_xattr_value_len, EVM_XATTR_HMAC, digest); 179 } 180 181 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 182 const char *req_xattr_value, size_t req_xattr_value_len, 183 char *digest) 184 { 185 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 186 req_xattr_value_len, IMA_XATTR_DIGEST, digest); 187 } 188 189 /* 190 * Calculate the hmac and update security.evm xattr 191 * 192 * Expects to be called with i_mutex locked. 193 */ 194 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 195 const char *xattr_value, size_t xattr_value_len) 196 { 197 struct inode *inode = dentry->d_inode; 198 struct evm_ima_xattr_data xattr_data; 199 int rc = 0; 200 201 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 202 xattr_value_len, xattr_data.digest); 203 if (rc == 0) { 204 xattr_data.type = EVM_XATTR_HMAC; 205 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM, 206 &xattr_data, 207 sizeof(xattr_data), 0); 208 } 209 else if (rc == -ENODATA) 210 rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM); 211 return rc; 212 } 213 214 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, 215 char *hmac_val) 216 { 217 struct shash_desc *desc; 218 219 desc = init_desc(EVM_XATTR_HMAC); 220 if (IS_ERR(desc)) { 221 printk(KERN_INFO "init_desc failed\n"); 222 return PTR_ERR(desc); 223 } 224 225 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); 226 hmac_add_misc(desc, inode, hmac_val); 227 kfree(desc); 228 return 0; 229 } 230 231 /* 232 * Get the key from the TPM for the SHA1-HMAC 233 */ 234 int evm_init_key(void) 235 { 236 struct key *evm_key; 237 struct encrypted_key_payload *ekp; 238 int rc = 0; 239 240 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 241 if (IS_ERR(evm_key)) 242 return -ENOENT; 243 244 down_read(&evm_key->sem); 245 ekp = evm_key->payload.data; 246 if (ekp->decrypted_datalen > MAX_KEY_SIZE) { 247 rc = -EINVAL; 248 goto out; 249 } 250 memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen); 251 out: 252 /* burn the original key contents */ 253 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 254 up_read(&evm_key->sem); 255 key_put(evm_key); 256 return rc; 257 } 258