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 <keys/encrypted-type.h> 22 #include <crypto/hash.h> 23 #include "evm.h" 24 25 #define EVMKEY "evm-key" 26 #define MAX_KEY_SIZE 128 27 static unsigned char evmkey[MAX_KEY_SIZE]; 28 static int evmkey_len = MAX_KEY_SIZE; 29 30 struct crypto_shash *hmac_tfm; 31 struct crypto_shash *hash_tfm; 32 33 static DEFINE_MUTEX(mutex); 34 35 static struct shash_desc *init_desc(char type) 36 { 37 long rc; 38 char *algo; 39 struct crypto_shash **tfm; 40 struct shash_desc *desc; 41 42 if (type == EVM_XATTR_HMAC) { 43 tfm = &hmac_tfm; 44 algo = evm_hmac; 45 } else { 46 tfm = &hash_tfm; 47 algo = evm_hash; 48 } 49 50 if (*tfm == NULL) { 51 mutex_lock(&mutex); 52 if (*tfm) 53 goto out; 54 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC); 55 if (IS_ERR(*tfm)) { 56 rc = PTR_ERR(*tfm); 57 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc); 58 *tfm = NULL; 59 mutex_unlock(&mutex); 60 return ERR_PTR(rc); 61 } 62 if (type == EVM_XATTR_HMAC) { 63 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len); 64 if (rc) { 65 crypto_free_shash(*tfm); 66 *tfm = NULL; 67 mutex_unlock(&mutex); 68 return ERR_PTR(rc); 69 } 70 } 71 out: 72 mutex_unlock(&mutex); 73 } 74 75 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm), 76 GFP_KERNEL); 77 if (!desc) 78 return ERR_PTR(-ENOMEM); 79 80 desc->tfm = *tfm; 81 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; 82 83 rc = crypto_shash_init(desc); 84 if (rc) { 85 kfree(desc); 86 return ERR_PTR(rc); 87 } 88 return desc; 89 } 90 91 /* Protect against 'cutting & pasting' security.evm xattr, include inode 92 * specific info. 93 * 94 * (Additional directory/file metadata needs to be added for more complete 95 * protection.) 96 */ 97 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode, 98 char *digest) 99 { 100 struct h_misc { 101 unsigned long ino; 102 __u32 generation; 103 uid_t uid; 104 gid_t gid; 105 umode_t mode; 106 } hmac_misc; 107 108 memset(&hmac_misc, 0, sizeof(hmac_misc)); 109 hmac_misc.ino = inode->i_ino; 110 hmac_misc.generation = inode->i_generation; 111 hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid); 112 hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid); 113 hmac_misc.mode = inode->i_mode; 114 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc)); 115 if (evm_hmac_attrs & EVM_ATTR_FSUUID) 116 crypto_shash_update(desc, inode->i_sb->s_uuid, 117 sizeof(inode->i_sb->s_uuid)); 118 crypto_shash_final(desc, digest); 119 } 120 121 /* 122 * Calculate the HMAC value across the set of protected security xattrs. 123 * 124 * Instead of retrieving the requested xattr, for performance, calculate 125 * the hmac using the requested xattr value. Don't alloc/free memory for 126 * each xattr, but attempt to re-use the previously allocated memory. 127 */ 128 static int evm_calc_hmac_or_hash(struct dentry *dentry, 129 const char *req_xattr_name, 130 const char *req_xattr_value, 131 size_t req_xattr_value_len, 132 char type, char *digest) 133 { 134 struct inode *inode = d_backing_inode(dentry); 135 struct shash_desc *desc; 136 char **xattrname; 137 size_t xattr_size = 0; 138 char *xattr_value = NULL; 139 int error; 140 int size; 141 142 if (!inode->i_op->getxattr) 143 return -EOPNOTSUPP; 144 desc = init_desc(type); 145 if (IS_ERR(desc)) 146 return PTR_ERR(desc); 147 148 error = -ENODATA; 149 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) { 150 if ((req_xattr_name && req_xattr_value) 151 && !strcmp(*xattrname, req_xattr_name)) { 152 error = 0; 153 crypto_shash_update(desc, (const u8 *)req_xattr_value, 154 req_xattr_value_len); 155 continue; 156 } 157 size = vfs_getxattr_alloc(dentry, *xattrname, 158 &xattr_value, xattr_size, GFP_NOFS); 159 if (size == -ENOMEM) { 160 error = -ENOMEM; 161 goto out; 162 } 163 if (size < 0) 164 continue; 165 166 error = 0; 167 xattr_size = size; 168 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); 169 } 170 hmac_add_misc(desc, inode, digest); 171 172 out: 173 kfree(xattr_value); 174 kfree(desc); 175 return error; 176 } 177 178 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, 179 const char *req_xattr_value, size_t req_xattr_value_len, 180 char *digest) 181 { 182 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 183 req_xattr_value_len, EVM_XATTR_HMAC, digest); 184 } 185 186 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, 187 const char *req_xattr_value, size_t req_xattr_value_len, 188 char *digest) 189 { 190 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, 191 req_xattr_value_len, IMA_XATTR_DIGEST, digest); 192 } 193 194 /* 195 * Calculate the hmac and update security.evm xattr 196 * 197 * Expects to be called with i_mutex locked. 198 */ 199 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, 200 const char *xattr_value, size_t xattr_value_len) 201 { 202 struct inode *inode = d_backing_inode(dentry); 203 struct evm_ima_xattr_data xattr_data; 204 int rc = 0; 205 206 rc = evm_calc_hmac(dentry, xattr_name, xattr_value, 207 xattr_value_len, xattr_data.digest); 208 if (rc == 0) { 209 xattr_data.type = EVM_XATTR_HMAC; 210 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM, 211 &xattr_data, 212 sizeof(xattr_data), 0); 213 } else if (rc == -ENODATA && inode->i_op->removexattr) { 214 rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM); 215 } 216 return rc; 217 } 218 219 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, 220 char *hmac_val) 221 { 222 struct shash_desc *desc; 223 224 desc = init_desc(EVM_XATTR_HMAC); 225 if (IS_ERR(desc)) { 226 pr_info("init_desc failed\n"); 227 return PTR_ERR(desc); 228 } 229 230 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); 231 hmac_add_misc(desc, inode, hmac_val); 232 kfree(desc); 233 return 0; 234 } 235 236 /* 237 * Get the key from the TPM for the SHA1-HMAC 238 */ 239 int evm_init_key(void) 240 { 241 struct key *evm_key; 242 struct encrypted_key_payload *ekp; 243 int rc = 0; 244 245 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); 246 if (IS_ERR(evm_key)) 247 return -ENOENT; 248 249 down_read(&evm_key->sem); 250 ekp = evm_key->payload.data[0]; 251 if (ekp->decrypted_datalen > MAX_KEY_SIZE) { 252 rc = -EINVAL; 253 goto out; 254 } 255 memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen); 256 out: 257 /* burn the original key contents */ 258 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); 259 up_read(&evm_key->sem); 260 key_put(evm_key); 261 return rc; 262 } 263