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
27static unsigned char evmkey[MAX_KEY_SIZE];
28static int evmkey_len = MAX_KEY_SIZE;
29
30struct crypto_shash *hmac_tfm;
31struct crypto_shash *hash_tfm;
32
33static DEFINE_MUTEX(mutex);
34
35static 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		}
71out:
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 */
97static 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 */
128static 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
172out:
173	kfree(xattr_value);
174	kfree(desc);
175	return error;
176}
177
178int 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
186int 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 */
199int 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
219int 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 */
239int 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);
256out:
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