1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2010 IBM Corporation
4  *
5  * Authors:
6  * Mimi Zohar <zohar@us.ibm.com>
7  *
8  * File: evm_secfs.c
9  *	- Used to signal when key is on keyring
10  *	- Get the key and enable EVM
11  */
12 
13 #include <linux/audit.h>
14 #include <linux/uaccess.h>
15 #include <linux/init.h>
16 #include <linux/mutex.h>
17 #include "evm.h"
18 
19 static struct dentry *evm_dir;
20 static struct dentry *evm_init_tpm;
21 static struct dentry *evm_symlink;
22 
23 #ifdef CONFIG_EVM_ADD_XATTRS
24 static struct dentry *evm_xattrs;
25 static DEFINE_MUTEX(xattr_list_mutex);
26 static int evm_xattrs_locked;
27 #endif
28 
29 /**
30  * evm_read_key - read() for <securityfs>/evm
31  *
32  * @filp: file pointer, not actually used
33  * @buf: where to put the result
34  * @count: maximum to send along
35  * @ppos: where to start
36  *
37  * Returns number of bytes read or error code, as appropriate
38  */
evm_read_key(struct file * filp,char __user * buf,size_t count,loff_t * ppos)39 static ssize_t evm_read_key(struct file *filp, char __user *buf,
40 			    size_t count, loff_t *ppos)
41 {
42 	char temp[80];
43 	ssize_t rc;
44 
45 	if (*ppos != 0)
46 		return 0;
47 
48 	sprintf(temp, "%d", (evm_initialized & ~EVM_SETUP_COMPLETE));
49 	rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
50 
51 	return rc;
52 }
53 
54 /**
55  * evm_write_key - write() for <securityfs>/evm
56  * @file: file pointer, not actually used
57  * @buf: where to get the data from
58  * @count: bytes sent
59  * @ppos: where to start
60  *
61  * Used to signal that key is on the kernel key ring.
62  * - get the integrity hmac key from the kernel key ring
63  * - create list of hmac protected extended attributes
64  * Returns number of bytes written or error code, as appropriate
65  */
evm_write_key(struct file * file,const char __user * buf,size_t count,loff_t * ppos)66 static ssize_t evm_write_key(struct file *file, const char __user *buf,
67 			     size_t count, loff_t *ppos)
68 {
69 	unsigned int i;
70 	int ret;
71 
72 	if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_SETUP_COMPLETE))
73 		return -EPERM;
74 
75 	ret = kstrtouint_from_user(buf, count, 0, &i);
76 
77 	if (ret)
78 		return ret;
79 
80 	/* Reject invalid values */
81 	if (!i || (i & ~EVM_INIT_MASK) != 0)
82 		return -EINVAL;
83 
84 	/*
85 	 * Don't allow a request to enable metadata writes if
86 	 * an HMAC key is loaded.
87 	 */
88 	if ((i & EVM_ALLOW_METADATA_WRITES) &&
89 	    (evm_initialized & EVM_INIT_HMAC) != 0)
90 		return -EPERM;
91 
92 	if (i & EVM_INIT_HMAC) {
93 		ret = evm_init_key();
94 		if (ret != 0)
95 			return ret;
96 		/* Forbid further writes after the symmetric key is loaded */
97 		i |= EVM_SETUP_COMPLETE;
98 	}
99 
100 	evm_initialized |= i;
101 
102 	/* Don't allow protected metadata modification if a symmetric key
103 	 * is loaded
104 	 */
105 	if (evm_initialized & EVM_INIT_HMAC)
106 		evm_initialized &= ~(EVM_ALLOW_METADATA_WRITES);
107 
108 	return count;
109 }
110 
111 static const struct file_operations evm_key_ops = {
112 	.read		= evm_read_key,
113 	.write		= evm_write_key,
114 };
115 
116 #ifdef CONFIG_EVM_ADD_XATTRS
117 /**
118  * evm_read_xattrs - read() for <securityfs>/evm_xattrs
119  *
120  * @filp: file pointer, not actually used
121  * @buf: where to put the result
122  * @count: maximum to send along
123  * @ppos: where to start
124  *
125  * Returns number of bytes read or error code, as appropriate
126  */
evm_read_xattrs(struct file * filp,char __user * buf,size_t count,loff_t * ppos)127 static ssize_t evm_read_xattrs(struct file *filp, char __user *buf,
128 			       size_t count, loff_t *ppos)
129 {
130 	char *temp;
131 	int offset = 0;
132 	ssize_t rc, size = 0;
133 	struct xattr_list *xattr;
134 
135 	if (*ppos != 0)
136 		return 0;
137 
138 	rc = mutex_lock_interruptible(&xattr_list_mutex);
139 	if (rc)
140 		return -ERESTARTSYS;
141 
142 	list_for_each_entry(xattr, &evm_config_xattrnames, list) {
143 		if (!xattr->enabled)
144 			continue;
145 
146 		size += strlen(xattr->name) + 1;
147 	}
148 
149 	temp = kmalloc(size + 1, GFP_KERNEL);
150 	if (!temp) {
151 		mutex_unlock(&xattr_list_mutex);
152 		return -ENOMEM;
153 	}
154 
155 	list_for_each_entry(xattr, &evm_config_xattrnames, list) {
156 		if (!xattr->enabled)
157 			continue;
158 
159 		sprintf(temp + offset, "%s\n", xattr->name);
160 		offset += strlen(xattr->name) + 1;
161 	}
162 
163 	mutex_unlock(&xattr_list_mutex);
164 	rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
165 
166 	kfree(temp);
167 
168 	return rc;
169 }
170 
171 /**
172  * evm_write_xattrs - write() for <securityfs>/evm_xattrs
173  * @file: file pointer, not actually used
174  * @buf: where to get the data from
175  * @count: bytes sent
176  * @ppos: where to start
177  *
178  * Returns number of bytes written or error code, as appropriate
179  */
evm_write_xattrs(struct file * file,const char __user * buf,size_t count,loff_t * ppos)180 static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
181 				size_t count, loff_t *ppos)
182 {
183 	int len, err;
184 	struct xattr_list *xattr, *tmp;
185 	struct audit_buffer *ab;
186 	struct iattr newattrs;
187 	struct inode *inode;
188 
189 	if (!capable(CAP_SYS_ADMIN) || evm_xattrs_locked)
190 		return -EPERM;
191 
192 	if (*ppos != 0)
193 		return -EINVAL;
194 
195 	if (count > XATTR_NAME_MAX)
196 		return -E2BIG;
197 
198 	ab = audit_log_start(audit_context(), GFP_KERNEL,
199 			     AUDIT_INTEGRITY_EVM_XATTR);
200 	if (!ab && IS_ENABLED(CONFIG_AUDIT))
201 		return -ENOMEM;
202 
203 	xattr = kmalloc(sizeof(struct xattr_list), GFP_KERNEL);
204 	if (!xattr) {
205 		err = -ENOMEM;
206 		goto out;
207 	}
208 
209 	xattr->enabled = true;
210 	xattr->name = memdup_user_nul(buf, count);
211 	if (IS_ERR(xattr->name)) {
212 		err = PTR_ERR(xattr->name);
213 		xattr->name = NULL;
214 		goto out;
215 	}
216 
217 	/* Remove any trailing newline */
218 	len = strlen(xattr->name);
219 	if (len && xattr->name[len-1] == '\n')
220 		xattr->name[len-1] = '\0';
221 
222 	audit_log_format(ab, "xattr=");
223 	audit_log_untrustedstring(ab, xattr->name);
224 
225 	if (strcmp(xattr->name, ".") == 0) {
226 		evm_xattrs_locked = 1;
227 		newattrs.ia_mode = S_IFREG | 0440;
228 		newattrs.ia_valid = ATTR_MODE;
229 		inode = evm_xattrs->d_inode;
230 		inode_lock(inode);
231 		err = simple_setattr(&nop_mnt_idmap, evm_xattrs, &newattrs);
232 		inode_unlock(inode);
233 		if (!err)
234 			err = count;
235 		goto out;
236 	}
237 
238 	if (strncmp(xattr->name, XATTR_SECURITY_PREFIX,
239 		    XATTR_SECURITY_PREFIX_LEN) != 0) {
240 		err = -EINVAL;
241 		goto out;
242 	}
243 
244 	/*
245 	 * xattr_list_mutex guards against races in evm_read_xattrs().
246 	 * Entries are only added to the evm_config_xattrnames list
247 	 * and never deleted. Therefore, the list is traversed
248 	 * using list_for_each_entry_lockless() without holding
249 	 * the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs()
250 	 * and evm_protected_xattr().
251 	 */
252 	mutex_lock(&xattr_list_mutex);
253 	list_for_each_entry(tmp, &evm_config_xattrnames, list) {
254 		if (strcmp(xattr->name, tmp->name) == 0) {
255 			err = -EEXIST;
256 			if (!tmp->enabled) {
257 				tmp->enabled = true;
258 				err = count;
259 			}
260 			mutex_unlock(&xattr_list_mutex);
261 			goto out;
262 		}
263 	}
264 	list_add_tail_rcu(&xattr->list, &evm_config_xattrnames);
265 	mutex_unlock(&xattr_list_mutex);
266 
267 	audit_log_format(ab, " res=0");
268 	audit_log_end(ab);
269 	return count;
270 out:
271 	audit_log_format(ab, " res=%d", (err < 0) ? err : 0);
272 	audit_log_end(ab);
273 	if (xattr) {
274 		kfree(xattr->name);
275 		kfree(xattr);
276 	}
277 	return err;
278 }
279 
280 static const struct file_operations evm_xattr_ops = {
281 	.read		= evm_read_xattrs,
282 	.write		= evm_write_xattrs,
283 };
284 
evm_init_xattrs(void)285 static int evm_init_xattrs(void)
286 {
287 	evm_xattrs = securityfs_create_file("evm_xattrs", 0660, evm_dir, NULL,
288 					    &evm_xattr_ops);
289 	if (!evm_xattrs || IS_ERR(evm_xattrs))
290 		return -EFAULT;
291 
292 	return 0;
293 }
294 #else
evm_init_xattrs(void)295 static int evm_init_xattrs(void)
296 {
297 	return 0;
298 }
299 #endif
300 
evm_init_secfs(void)301 int __init evm_init_secfs(void)
302 {
303 	int error = 0;
304 
305 	evm_dir = securityfs_create_dir("evm", integrity_dir);
306 	if (!evm_dir || IS_ERR(evm_dir))
307 		return -EFAULT;
308 
309 	evm_init_tpm = securityfs_create_file("evm", 0660,
310 					      evm_dir, NULL, &evm_key_ops);
311 	if (!evm_init_tpm || IS_ERR(evm_init_tpm)) {
312 		error = -EFAULT;
313 		goto out;
314 	}
315 
316 	evm_symlink = securityfs_create_symlink("evm", NULL,
317 						"integrity/evm/evm", NULL);
318 	if (!evm_symlink || IS_ERR(evm_symlink)) {
319 		error = -EFAULT;
320 		goto out;
321 	}
322 
323 	if (evm_init_xattrs() != 0) {
324 		error = -EFAULT;
325 		goto out;
326 	}
327 
328 	return 0;
329 out:
330 	securityfs_remove(evm_symlink);
331 	securityfs_remove(evm_init_tpm);
332 	securityfs_remove(evm_dir);
333 	return error;
334 }
335