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 = from_kuid(&init_user_ns, inode->i_uid); 110 hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid); 111 hmac_misc.mode = inode->i_mode; 112 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof hmac_misc); 113 if (evm_hmac_version > 1) 114 crypto_shash_update(desc, inode->i_sb->s_uuid, 115 sizeof(inode->i_sb->s_uuid)); 116 crypto_shash_final(desc, digest); 117 } 118 119 /* 120 * Calculate the HMAC value across the set of protected security xattrs. 121 * 122 * Instead of retrieving the requested xattr, for performance, calculate 123 * the hmac using the requested xattr value. Don't alloc/free memory for 124 * each xattr, but attempt to re-use the previously allocated memory. 125 */ 126 static int evm_calc_hmac_or_hash(struct dentry *dentry, 127 const char *req_xattr_name, 128 const char *req_xattr_value, 129 size_t req_xattr_value_len, 130 char type, char *digest) 131 { 132 struct inode *inode = dentry->d_inode; 133 struct shash_desc *desc; 134 char **xattrname; 135 size_t xattr_size = 0; 136 char *xattr_value = NULL; 137 int error; 138 int size; 139 140 if (!inode->i_op || !inode->i_op->getxattr) 141 return -EOPNOTSUPP; 142 desc = init_desc(type); 143 if (IS_ERR(desc)) 144 return PTR_ERR(desc); 145 146 error = -ENODATA; 147 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) { 148 if ((req_xattr_name && req_xattr_value) 149 && !strcmp(*xattrname, req_xattr_name)) { 150 error = 0; 151 crypto_shash_update(desc, (const u8 *)req_xattr_value, 152 req_xattr_value_len); 153 continue; 154 } 155 size = vfs_getxattr_alloc(dentry, *xattrname, 156 &xattr_value, xattr_size, GFP_NOFS); 157 if (size == -ENOMEM) { 158 error = -ENOMEM; 159 goto out; 160 } 161 if (size < 0) 162 continue; 163 164 error = 0; 165 xattr_size = size; 166 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 167 } 168 hmac_add_misc(desc, inode, digest); 169 170 out: 171 kfree(xattr_value); 172 kfree(desc); 173 return error; 174 } 175 176 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 177 const char *req_xattr_value, size_t req_xattr_value_len, 178 char *digest) 179 { 180 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 181 req_xattr_value_len, EVM_XATTR_HMAC, digest); 182 } 183 184 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 185 const char *req_xattr_value, size_t req_xattr_value_len, 186 char *digest) 187 { 188 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 189 req_xattr_value_len, IMA_XATTR_DIGEST, digest); 190 } 191 192 /* 193 * Calculate the hmac and update security.evm xattr 194 * 195 * Expects to be called with i_mutex locked. 196 */ 197 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 198 const char *xattr_value, size_t xattr_value_len) 199 { 200 struct inode *inode = dentry->d_inode; 201 struct evm_ima_xattr_data xattr_data; 202 int rc = 0; 203 204 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 205 xattr_value_len, xattr_data.digest); 206 if (rc == 0) { 207 xattr_data.type = EVM_XATTR_HMAC; 208 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM, 209 &xattr_data, 210 sizeof(xattr_data), 0); 211 } else if (rc == -ENODATA && inode->i_op->removexattr) { 212 rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM); 213 } 214 return rc; 215 } 216 217 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, 218 char *hmac_val) 219 { 220 struct shash_desc *desc; 221 222 desc = init_desc(EVM_XATTR_HMAC); 223 if (IS_ERR(desc)) { 224 printk(KERN_INFO "init_desc failed\n"); 225 return PTR_ERR(desc); 226 } 227 228 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); 229 hmac_add_misc(desc, inode, hmac_val); 230 kfree(desc); 231 return 0; 232 } 233 234 /* 235 * Get the key from the TPM for the SHA1-HMAC 236 */ 237 int evm_init_key(void) 238 { 239 struct key *evm_key; 240 struct encrypted_key_payload *ekp; 241 int rc = 0; 242 243 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 244 if (IS_ERR(evm_key)) 245 return -ENOENT; 246 247 down_read(&evm_key->sem); 248 ekp = evm_key->payload.data; 249 if (ekp->decrypted_datalen > MAX_KEY_SIZE) { 250 rc = -EINVAL; 251 goto out; 252 } 253 memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen); 254 out: 255 /* burn the original key contents */ 256 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 257 up_read(&evm_key->sem); 258 key_put(evm_key); 259 return rc; 260 } 261