2 * Copyright (C) 2005-2010 IBM Corporation
5 * Mimi Zohar <zohar@us.ibm.com>
6 * Kylene Hall <kjhall@us.ibm.com>
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.
13 * Using root's kernel master key (kmk), calculate the HMAC
16 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
18 #include <linux/export.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 <crypto/hash_info.h>
27 #define EVMKEY "evm-key"
28 #define MAX_KEY_SIZE 128
29 static unsigned char evmkey[MAX_KEY_SIZE];
30 static const int evmkey_len = MAX_KEY_SIZE;
32 struct crypto_shash *hmac_tfm;
33 static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
35 static DEFINE_MUTEX(mutex);
37 #define EVM_SET_KEY_BUSY 0
39 static unsigned long evm_set_key_flags;
41 static const char evm_hmac[] = "hmac(sha1)";
44 * evm_set_key() - set EVM HMAC key from the kernel
45 * @key: pointer to a buffer with the key data
46 * @size: length of the key data
48 * This function allows setting the EVM HMAC key from the kernel
49 * without using the "encrypted" key subsystem keys. It can be used
50 * by the crypto HW kernel module which has its own way of managing
53 * key length should be between 32 and 128 bytes long
55 int evm_set_key(void *key, size_t keylen)
60 if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
63 if (keylen > MAX_KEY_SIZE)
65 memcpy(evmkey, key, keylen);
66 evm_initialized |= EVM_INIT_HMAC;
67 pr_info("key initialized\n");
70 clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
72 pr_err("key initialization failed\n");
75 EXPORT_SYMBOL_GPL(evm_set_key);
77 static struct shash_desc *init_desc(char type, uint8_t hash_algo)
81 struct crypto_shash **tfm;
82 struct shash_desc *desc;
84 if (type == EVM_XATTR_HMAC) {
85 if (!(evm_initialized & EVM_INIT_HMAC)) {
86 pr_err_once("HMAC key is not set\n");
87 return ERR_PTR(-ENOKEY);
92 tfm = &evm_tfm[hash_algo];
93 algo = hash_algo_name[hash_algo];
100 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
103 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
105 mutex_unlock(&mutex);
108 if (type == EVM_XATTR_HMAC) {
109 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
111 crypto_free_shash(*tfm);
113 mutex_unlock(&mutex);
118 mutex_unlock(&mutex);
121 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
124 return ERR_PTR(-ENOMEM);
127 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
129 rc = crypto_shash_init(desc);
137 /* Protect against 'cutting & pasting' security.evm xattr, include inode
140 * (Additional directory/file metadata needs to be added for more complete
143 static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
144 char type, char *digest)
154 memset(&hmac_misc, 0, sizeof(hmac_misc));
155 /* Don't include the inode or generation number in portable
158 if (type != EVM_XATTR_PORTABLE_DIGSIG) {
159 hmac_misc.ino = inode->i_ino;
160 hmac_misc.generation = inode->i_generation;
162 /* The hmac uid and gid must be encoded in the initial user
163 * namespace (not the filesystems user namespace) as encoding
164 * them in the filesystems user namespace allows an attack
165 * where first they are written in an unprivileged fuse mount
166 * of a filesystem and then the system is tricked to mount the
167 * filesystem for real on next boot and trust it because
168 * everything is signed.
170 hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
171 hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
172 hmac_misc.mode = inode->i_mode;
173 crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
174 if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
175 type != EVM_XATTR_PORTABLE_DIGSIG)
176 crypto_shash_update(desc, &inode->i_sb->s_uuid.b[0],
177 sizeof(inode->i_sb->s_uuid));
178 crypto_shash_final(desc, digest);
182 * Calculate the HMAC value across the set of protected security xattrs.
184 * Instead of retrieving the requested xattr, for performance, calculate
185 * the hmac using the requested xattr value. Don't alloc/free memory for
186 * each xattr, but attempt to re-use the previously allocated memory.
188 static int evm_calc_hmac_or_hash(struct dentry *dentry,
189 const char *req_xattr_name,
190 const char *req_xattr_value,
191 size_t req_xattr_value_len,
192 uint8_t type, struct evm_digest *data)
194 struct inode *inode = d_backing_inode(dentry);
195 struct xattr_list *xattr;
196 struct shash_desc *desc;
197 size_t xattr_size = 0;
198 char *xattr_value = NULL;
201 bool ima_present = false;
203 if (!(inode->i_opflags & IOP_XATTR) ||
204 inode->i_sb->s_user_ns != &init_user_ns)
207 desc = init_desc(type, data->hdr.algo);
209 return PTR_ERR(desc);
211 data->hdr.length = crypto_shash_digestsize(desc->tfm);
214 list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
217 if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
220 if ((req_xattr_name && req_xattr_value)
221 && !strcmp(xattr->name, req_xattr_name)) {
223 crypto_shash_update(desc, (const u8 *)req_xattr_value,
224 req_xattr_value_len);
229 size = vfs_getxattr_alloc(dentry, xattr->name,
230 &xattr_value, xattr_size, GFP_NOFS);
231 if (size == -ENOMEM) {
240 crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
244 hmac_add_misc(desc, inode, type, data->digest);
246 /* Portable EVM signatures must include an IMA hash */
247 if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
255 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
256 const char *req_xattr_value, size_t req_xattr_value_len,
257 struct evm_digest *data)
259 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
260 req_xattr_value_len, EVM_XATTR_HMAC, data);
263 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
264 const char *req_xattr_value, size_t req_xattr_value_len,
265 char type, struct evm_digest *data)
267 return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
268 req_xattr_value_len, type, data);
271 static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
273 const struct evm_ima_xattr_data *xattr_data = NULL;
274 struct integrity_iint_cache *iint;
277 iint = integrity_iint_find(inode);
278 if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
281 /* Do this the hard way */
282 rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
289 if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
300 * Calculate the hmac and update security.evm xattr
302 * Expects to be called with i_mutex locked.
304 int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
305 const char *xattr_value, size_t xattr_value_len)
307 struct inode *inode = d_backing_inode(dentry);
308 struct evm_digest data;
312 * Don't permit any transformation of the EVM xattr if the signature
313 * is of an immutable type
315 rc = evm_is_immutable(dentry, inode);
321 data.hdr.algo = HASH_ALGO_SHA1;
322 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
323 xattr_value_len, &data);
325 data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
326 rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
327 &data.hdr.xattr.data[1],
328 SHA1_DIGEST_SIZE + 1, 0);
329 } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
330 rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
335 int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
338 struct shash_desc *desc;
340 desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
342 pr_info("init_desc failed\n");
343 return PTR_ERR(desc);
346 crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
347 hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
353 * Get the key from the TPM for the SHA1-HMAC
355 int evm_init_key(void)
358 struct encrypted_key_payload *ekp;
361 evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
365 down_read(&evm_key->sem);
366 ekp = evm_key->payload.data[0];
368 rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
370 /* burn the original key contents */
371 memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
372 up_read(&evm_key->sem);