xref: /linux/security/integrity/evm/evm_crypto.c (revision d91517839e5d95adc0cf4b28caa7af62a71de526)
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