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TOMOYO Linux Cross Reference
Linux/security/integrity/evm/evm_crypto.c

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  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 

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