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 = dentry->d_inode;
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 = dentry->d_inode;
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;
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