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 * implements evm_inode_setxattr, evm_inode_post_setxattr,
14 * evm_inode_removexattr, and evm_verifyxattr
17 #include <linux/module.h>
18 #include <linux/crypto.h>
19 #include <linux/xattr.h>
20 #include <linux/integrity.h>
21 #include <linux/evm.h>
22 #include <crypto/hash.h>
27 char *evm_hmac = "hmac(sha1)";
29 char *evm_config_xattrnames[] = {
30 #ifdef CONFIG_SECURITY_SELINUX
33 #ifdef CONFIG_SECURITY_SMACK
40 static int evm_fixmode;
41 static int __init evm_set_fixmode(char *str)
43 if (strncmp(str, "fix", 3) == 0)
47 __setup("evm=", evm_set_fixmode);
50 * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
52 * Compute the HMAC on the dentry's protected set of extended attributes
53 * and compare it against the stored security.evm xattr.
56 * - use the previoulsy retrieved xattr value and length to calculate the
58 * - cache the verification result in the iint, when available.
60 * Returns integrity status
62 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
63 const char *xattr_name,
65 size_t xattr_value_len,
66 struct integrity_iint_cache *iint)
68 struct evm_ima_xattr_data xattr_data;
69 enum integrity_status evm_status = INTEGRITY_PASS;
72 if (iint && iint->evm_status == INTEGRITY_PASS)
73 return iint->evm_status;
75 /* if status is not PASS, try to check again - against -ENOMEM */
77 rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
78 xattr_value_len, xattr_data.digest);
80 evm_status = (rc == -ENODATA)
81 ? INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
85 xattr_data.type = EVM_XATTR_HMAC;
86 rc = vfs_xattr_cmp(dentry, XATTR_NAME_EVM, (u8 *)&xattr_data,
87 sizeof xattr_data, GFP_NOFS);
89 evm_status = (rc == -ENODATA)
90 ? INTEGRITY_NOLABEL : INTEGRITY_FAIL;
93 iint->evm_status = evm_status;
97 static int evm_protected_xattr(const char *req_xattr_name)
103 namelen = strlen(req_xattr_name);
104 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
105 if ((strlen(*xattrname) == namelen)
106 && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
110 if (strncmp(req_xattr_name,
111 *xattrname + XATTR_SECURITY_PREFIX_LEN,
112 strlen(req_xattr_name)) == 0) {
121 * evm_verifyxattr - verify the integrity of the requested xattr
122 * @dentry: object of the verify xattr
123 * @xattr_name: requested xattr
124 * @xattr_value: requested xattr value
125 * @xattr_value_len: requested xattr value length
127 * Calculate the HMAC for the given dentry and verify it against the stored
128 * security.evm xattr. For performance, use the xattr value and length
129 * previously retrieved to calculate the HMAC.
131 * Returns the xattr integrity status.
133 * This function requires the caller to lock the inode's i_mutex before it
136 enum integrity_status evm_verifyxattr(struct dentry *dentry,
137 const char *xattr_name,
138 void *xattr_value, size_t xattr_value_len,
139 struct integrity_iint_cache *iint)
141 if (!evm_initialized || !evm_protected_xattr(xattr_name))
142 return INTEGRITY_UNKNOWN;
145 iint = integrity_iint_find(dentry->d_inode);
147 return INTEGRITY_UNKNOWN;
149 return evm_verify_hmac(dentry, xattr_name, xattr_value,
150 xattr_value_len, iint);
152 EXPORT_SYMBOL_GPL(evm_verifyxattr);
155 * evm_verify_current_integrity - verify the dentry's metadata integrity
156 * @dentry: pointer to the affected dentry
158 * Verify and return the dentry's metadata integrity. The exceptions are
159 * before EVM is initialized or in 'fix' mode.
161 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
163 struct inode *inode = dentry->d_inode;
165 if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
167 return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
171 * evm_protect_xattr - protect the EVM extended attribute
173 * Prevent security.evm from being modified or removed without the
174 * necessary permissions or when the existing value is invalid.
176 * The posix xattr acls are 'system' prefixed, which normally would not
177 * affect security.evm. An interesting side affect of writing posix xattr
178 * acls is their modifying of the i_mode, which is included in security.evm.
179 * For posix xattr acls only, permit security.evm, even if it currently
180 * doesn't exist, to be updated.
182 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
183 const void *xattr_value, size_t xattr_value_len)
185 enum integrity_status evm_status;
187 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
188 if (!capable(CAP_SYS_ADMIN))
190 } else if (!evm_protected_xattr(xattr_name)) {
191 if (!posix_xattr_acl(xattr_name))
193 evm_status = evm_verify_current_integrity(dentry);
194 if ((evm_status == INTEGRITY_PASS) ||
195 (evm_status == INTEGRITY_NOXATTRS))
199 evm_status = evm_verify_current_integrity(dentry);
200 return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
204 * evm_inode_setxattr - protect the EVM extended attribute
205 * @dentry: pointer to the affected dentry
206 * @xattr_name: pointer to the affected extended attribute name
207 * @xattr_value: pointer to the new extended attribute value
208 * @xattr_value_len: pointer to the new extended attribute value length
210 * Before allowing the 'security.evm' protected xattr to be updated,
211 * verify the existing value is valid. As only the kernel should have
212 * access to the EVM encrypted key needed to calculate the HMAC, prevent
213 * userspace from writing HMAC value. Writing 'security.evm' requires
214 * requires CAP_SYS_ADMIN privileges.
216 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
217 const void *xattr_value, size_t xattr_value_len)
219 const struct evm_ima_xattr_data *xattr_data = xattr_value;
221 if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
222 if (!xattr_value_len)
224 if (xattr_data->type != EVM_IMA_XATTR_DIGSIG)
227 return evm_protect_xattr(dentry, xattr_name, xattr_value,
232 * evm_inode_removexattr - protect the EVM extended attribute
233 * @dentry: pointer to the affected dentry
234 * @xattr_name: pointer to the affected extended attribute name
236 * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
237 * the current value is valid.
239 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
241 return evm_protect_xattr(dentry, xattr_name, NULL, 0);
245 * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
246 * @dentry: pointer to the affected dentry
247 * @xattr_name: pointer to the affected extended attribute name
248 * @xattr_value: pointer to the new extended attribute value
249 * @xattr_value_len: pointer to the new extended attribute value length
251 * Update the HMAC stored in 'security.evm' to reflect the change.
253 * No need to take the i_mutex lock here, as this function is called from
254 * __vfs_setxattr_noperm(). The caller of which has taken the inode's
257 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
258 const void *xattr_value, size_t xattr_value_len)
260 if (!evm_initialized || (!evm_protected_xattr(xattr_name)
261 && !posix_xattr_acl(xattr_name)))
264 evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
269 * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
270 * @dentry: pointer to the affected dentry
271 * @xattr_name: pointer to the affected extended attribute name
273 * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
275 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
277 struct inode *inode = dentry->d_inode;
279 if (!evm_initialized || !evm_protected_xattr(xattr_name))
282 mutex_lock(&inode->i_mutex);
283 evm_update_evmxattr(dentry, xattr_name, NULL, 0);
284 mutex_unlock(&inode->i_mutex);
289 * evm_inode_setattr - prevent updating an invalid EVM extended attribute
290 * @dentry: pointer to the affected dentry
292 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
294 unsigned int ia_valid = attr->ia_valid;
295 enum integrity_status evm_status;
297 if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
299 evm_status = evm_verify_current_integrity(dentry);
300 if ((evm_status == INTEGRITY_PASS) ||
301 (evm_status == INTEGRITY_NOXATTRS))
307 * evm_inode_post_setattr - update 'security.evm' after modifying metadata
308 * @dentry: pointer to the affected dentry
309 * @ia_valid: for the UID and GID status
311 * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
314 * This function is called from notify_change(), which expects the caller
315 * to lock the inode's i_mutex.
317 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
319 if (!evm_initialized)
322 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
323 evm_update_evmxattr(dentry, NULL, NULL, 0);
328 * evm_inode_init_security - initializes security.evm
330 int evm_inode_init_security(struct inode *inode,
331 const struct xattr *lsm_xattr,
332 struct xattr *evm_xattr)
334 struct evm_ima_xattr_data *xattr_data;
337 if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
340 xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
344 xattr_data->type = EVM_XATTR_HMAC;
345 rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
349 evm_xattr->value = xattr_data;
350 evm_xattr->value_len = sizeof(*xattr_data);
351 evm_xattr->name = kstrdup(XATTR_EVM_SUFFIX, GFP_NOFS);
357 EXPORT_SYMBOL_GPL(evm_inode_init_security);
359 static int __init init_evm(void)
363 error = evm_init_secfs();
365 printk(KERN_INFO "EVM: Error registering secfs\n");
372 static void __exit cleanup_evm(void)
376 crypto_free_shash(hmac_tfm);
380 * evm_display_config - list the EVM protected security extended attributes
382 static int __init evm_display_config(void)
386 for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
387 printk(KERN_INFO "EVM: %s\n", *xattrname);
391 pure_initcall(evm_display_config);
392 late_initcall(init_evm);
394 MODULE_DESCRIPTION("Extended Verification Module");
395 MODULE_LICENSE("GPL");