Linux 2.6.31-rc6
[linux-2.6] / security / integrity / ima / ima_policy.c
1 /*
2  * Copyright (C) 2008 IBM Corporation
3  * Author: Mimi Zohar <zohar@us.ibm.com>
4  *
5  * This program is free software; you can redistribute it and/or modify
6  * it under the terms of the GNU General Public License as published by
7  * the Free Software Foundation, version 2 of the License.
8  *
9  * ima_policy.c
10  *      - initialize default measure policy rules
11  *
12  */
13 #include <linux/module.h>
14 #include <linux/list.h>
15 #include <linux/security.h>
16 #include <linux/magic.h>
17 #include <linux/parser.h>
18
19 #include "ima.h"
20
21 /* flags definitions */
22 #define IMA_FUNC        0x0001
23 #define IMA_MASK        0x0002
24 #define IMA_FSMAGIC     0x0004
25 #define IMA_UID         0x0008
26
27 enum ima_action { UNKNOWN = -1, DONT_MEASURE = 0, MEASURE };
28
29 #define MAX_LSM_RULES 6
30 enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
31         LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE
32 };
33
34 struct ima_measure_rule_entry {
35         struct list_head list;
36         enum ima_action action;
37         unsigned int flags;
38         enum ima_hooks func;
39         int mask;
40         unsigned long fsmagic;
41         uid_t uid;
42         struct {
43                 void *rule;     /* LSM file metadata specific */
44                 int type;       /* audit type */
45         } lsm[MAX_LSM_RULES];
46 };
47
48 /*
49  * Without LSM specific knowledge, the default policy can only be
50  * written in terms of .action, .func, .mask, .fsmagic, and .uid
51  */
52
53 /*
54  * The minimum rule set to allow for full TCB coverage.  Measures all files
55  * opened or mmap for exec and everything read by root.  Dangerous because
56  * normal users can easily run the machine out of memory simply building
57  * and running executables.
58  */
59 static struct ima_measure_rule_entry default_rules[] = {
60         {.action = DONT_MEASURE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC},
61         {.action = DONT_MEASURE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC},
62         {.action = DONT_MEASURE,.fsmagic = DEBUGFS_MAGIC,.flags = IMA_FSMAGIC},
63         {.action = DONT_MEASURE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC},
64         {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
65         {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
66         {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC,
67          .flags = IMA_FUNC | IMA_MASK},
68         {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC,
69          .flags = IMA_FUNC | IMA_MASK},
70         {.action = MEASURE,.func = PATH_CHECK,.mask = MAY_READ,.uid = 0,
71          .flags = IMA_FUNC | IMA_MASK | IMA_UID},
72 };
73
74 static LIST_HEAD(measure_default_rules);
75 static LIST_HEAD(measure_policy_rules);
76 static struct list_head *ima_measure;
77
78 static DEFINE_MUTEX(ima_measure_mutex);
79
80 static bool ima_use_tcb __initdata;
81 static int __init default_policy_setup(char *str)
82 {
83         ima_use_tcb = 1;
84         return 1;
85 }
86 __setup("ima_tcb", default_policy_setup);
87
88 /**
89  * ima_match_rules - determine whether an inode matches the measure rule.
90  * @rule: a pointer to a rule
91  * @inode: a pointer to an inode
92  * @func: LIM hook identifier
93  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
94  *
95  * Returns true on rule match, false on failure.
96  */
97 static bool ima_match_rules(struct ima_measure_rule_entry *rule,
98                             struct inode *inode, enum ima_hooks func, int mask)
99 {
100         struct task_struct *tsk = current;
101         int i;
102
103         if ((rule->flags & IMA_FUNC) && rule->func != func)
104                 return false;
105         if ((rule->flags & IMA_MASK) && rule->mask != mask)
106                 return false;
107         if ((rule->flags & IMA_FSMAGIC)
108             && rule->fsmagic != inode->i_sb->s_magic)
109                 return false;
110         if ((rule->flags & IMA_UID) && rule->uid != tsk->cred->uid)
111                 return false;
112         for (i = 0; i < MAX_LSM_RULES; i++) {
113                 int rc = 0;
114                 u32 osid, sid;
115
116                 if (!rule->lsm[i].rule)
117                         continue;
118
119                 switch (i) {
120                 case LSM_OBJ_USER:
121                 case LSM_OBJ_ROLE:
122                 case LSM_OBJ_TYPE:
123                         security_inode_getsecid(inode, &osid);
124                         rc = security_filter_rule_match(osid,
125                                                         rule->lsm[i].type,
126                                                         Audit_equal,
127                                                         rule->lsm[i].rule,
128                                                         NULL);
129                         break;
130                 case LSM_SUBJ_USER:
131                 case LSM_SUBJ_ROLE:
132                 case LSM_SUBJ_TYPE:
133                         security_task_getsecid(tsk, &sid);
134                         rc = security_filter_rule_match(sid,
135                                                         rule->lsm[i].type,
136                                                         Audit_equal,
137                                                         rule->lsm[i].rule,
138                                                         NULL);
139                 default:
140                         break;
141                 }
142                 if (!rc)
143                         return false;
144         }
145         return true;
146 }
147
148 /**
149  * ima_match_policy - decision based on LSM and other conditions
150  * @inode: pointer to an inode for which the policy decision is being made
151  * @func: IMA hook identifier
152  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
153  *
154  * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
155  * conditions.
156  *
157  * (There is no need for locking when walking the policy list,
158  * as elements in the list are never deleted, nor does the list
159  * change.)
160  */
161 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask)
162 {
163         struct ima_measure_rule_entry *entry;
164
165         list_for_each_entry(entry, ima_measure, list) {
166                 bool rc;
167
168                 rc = ima_match_rules(entry, inode, func, mask);
169                 if (rc)
170                         return entry->action;
171         }
172         return 0;
173 }
174
175 /**
176  * ima_init_policy - initialize the default measure rules.
177  *
178  * ima_measure points to either the measure_default_rules or the
179  * the new measure_policy_rules.
180  */
181 void __init ima_init_policy(void)
182 {
183         int i, entries;
184
185         /* if !ima_use_tcb set entries = 0 so we load NO default rules */
186         if (ima_use_tcb)
187                 entries = ARRAY_SIZE(default_rules);
188         else
189                 entries = 0;
190
191         for (i = 0; i < entries; i++)
192                 list_add_tail(&default_rules[i].list, &measure_default_rules);
193         ima_measure = &measure_default_rules;
194 }
195
196 /**
197  * ima_update_policy - update default_rules with new measure rules
198  *
199  * Called on file .release to update the default rules with a complete new
200  * policy.  Once updated, the policy is locked, no additional rules can be
201  * added to the policy.
202  */
203 void ima_update_policy(void)
204 {
205         const char *op = "policy_update";
206         const char *cause = "already exists";
207         int result = 1;
208         int audit_info = 0;
209
210         if (ima_measure == &measure_default_rules) {
211                 ima_measure = &measure_policy_rules;
212                 cause = "complete";
213                 result = 0;
214         }
215         integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
216                             NULL, op, cause, result, audit_info);
217 }
218
219 enum {
220         Opt_err = -1,
221         Opt_measure = 1, Opt_dont_measure,
222         Opt_obj_user, Opt_obj_role, Opt_obj_type,
223         Opt_subj_user, Opt_subj_role, Opt_subj_type,
224         Opt_func, Opt_mask, Opt_fsmagic, Opt_uid
225 };
226
227 static match_table_t policy_tokens = {
228         {Opt_measure, "measure"},
229         {Opt_dont_measure, "dont_measure"},
230         {Opt_obj_user, "obj_user=%s"},
231         {Opt_obj_role, "obj_role=%s"},
232         {Opt_obj_type, "obj_type=%s"},
233         {Opt_subj_user, "subj_user=%s"},
234         {Opt_subj_role, "subj_role=%s"},
235         {Opt_subj_type, "subj_type=%s"},
236         {Opt_func, "func=%s"},
237         {Opt_mask, "mask=%s"},
238         {Opt_fsmagic, "fsmagic=%s"},
239         {Opt_uid, "uid=%s"},
240         {Opt_err, NULL}
241 };
242
243 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry,
244                              char *args, int lsm_rule, int audit_type)
245 {
246         int result;
247
248         entry->lsm[lsm_rule].type = audit_type;
249         result = security_filter_rule_init(entry->lsm[lsm_rule].type,
250                                            Audit_equal, args,
251                                            &entry->lsm[lsm_rule].rule);
252         return result;
253 }
254
255 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry)
256 {
257         struct audit_buffer *ab;
258         char *p;
259         int result = 0;
260
261         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);
262
263         entry->action = -1;
264         while ((p = strsep(&rule, " \n")) != NULL) {
265                 substring_t args[MAX_OPT_ARGS];
266                 int token;
267                 unsigned long lnum;
268
269                 if (result < 0)
270                         break;
271                 if (!*p)
272                         continue;
273                 token = match_token(p, policy_tokens, args);
274                 switch (token) {
275                 case Opt_measure:
276                         audit_log_format(ab, "%s ", "measure");
277                         entry->action = MEASURE;
278                         break;
279                 case Opt_dont_measure:
280                         audit_log_format(ab, "%s ", "dont_measure");
281                         entry->action = DONT_MEASURE;
282                         break;
283                 case Opt_func:
284                         audit_log_format(ab, "func=%s ", args[0].from);
285                         if (strcmp(args[0].from, "PATH_CHECK") == 0)
286                                 entry->func = PATH_CHECK;
287                         else if (strcmp(args[0].from, "FILE_MMAP") == 0)
288                                 entry->func = FILE_MMAP;
289                         else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
290                                 entry->func = BPRM_CHECK;
291                         else
292                                 result = -EINVAL;
293                         if (!result)
294                                 entry->flags |= IMA_FUNC;
295                         break;
296                 case Opt_mask:
297                         audit_log_format(ab, "mask=%s ", args[0].from);
298                         if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
299                                 entry->mask = MAY_EXEC;
300                         else if (strcmp(args[0].from, "MAY_WRITE") == 0)
301                                 entry->mask = MAY_WRITE;
302                         else if (strcmp(args[0].from, "MAY_READ") == 0)
303                                 entry->mask = MAY_READ;
304                         else if (strcmp(args[0].from, "MAY_APPEND") == 0)
305                                 entry->mask = MAY_APPEND;
306                         else
307                                 result = -EINVAL;
308                         if (!result)
309                                 entry->flags |= IMA_MASK;
310                         break;
311                 case Opt_fsmagic:
312                         audit_log_format(ab, "fsmagic=%s ", args[0].from);
313                         result = strict_strtoul(args[0].from, 16,
314                                                 &entry->fsmagic);
315                         if (!result)
316                                 entry->flags |= IMA_FSMAGIC;
317                         break;
318                 case Opt_uid:
319                         audit_log_format(ab, "uid=%s ", args[0].from);
320                         result = strict_strtoul(args[0].from, 10, &lnum);
321                         if (!result) {
322                                 entry->uid = (uid_t) lnum;
323                                 if (entry->uid != lnum)
324                                         result = -EINVAL;
325                                 else
326                                         entry->flags |= IMA_UID;
327                         }
328                         break;
329                 case Opt_obj_user:
330                         audit_log_format(ab, "obj_user=%s ", args[0].from);
331                         result = ima_lsm_rule_init(entry, args[0].from,
332                                                    LSM_OBJ_USER,
333                                                    AUDIT_OBJ_USER);
334                         break;
335                 case Opt_obj_role:
336                         audit_log_format(ab, "obj_role=%s ", args[0].from);
337                         result = ima_lsm_rule_init(entry, args[0].from,
338                                                    LSM_OBJ_ROLE,
339                                                    AUDIT_OBJ_ROLE);
340                         break;
341                 case Opt_obj_type:
342                         audit_log_format(ab, "obj_type=%s ", args[0].from);
343                         result = ima_lsm_rule_init(entry, args[0].from,
344                                                    LSM_OBJ_TYPE,
345                                                    AUDIT_OBJ_TYPE);
346                         break;
347                 case Opt_subj_user:
348                         audit_log_format(ab, "subj_user=%s ", args[0].from);
349                         result = ima_lsm_rule_init(entry, args[0].from,
350                                                    LSM_SUBJ_USER,
351                                                    AUDIT_SUBJ_USER);
352                         break;
353                 case Opt_subj_role:
354                         audit_log_format(ab, "subj_role=%s ", args[0].from);
355                         result = ima_lsm_rule_init(entry, args[0].from,
356                                                    LSM_SUBJ_ROLE,
357                                                    AUDIT_SUBJ_ROLE);
358                         break;
359                 case Opt_subj_type:
360                         audit_log_format(ab, "subj_type=%s ", args[0].from);
361                         result = ima_lsm_rule_init(entry, args[0].from,
362                                                    LSM_SUBJ_TYPE,
363                                                    AUDIT_SUBJ_TYPE);
364                         break;
365                 case Opt_err:
366                         audit_log_format(ab, "UNKNOWN=%s ", p);
367                         break;
368                 }
369         }
370         if (entry->action == UNKNOWN)
371                 result = -EINVAL;
372
373         audit_log_format(ab, "res=%d", !result ? 0 : 1);
374         audit_log_end(ab);
375         return result;
376 }
377
378 /**
379  * ima_parse_add_rule - add a rule to measure_policy_rules
380  * @rule - ima measurement policy rule
381  *
382  * Uses a mutex to protect the policy list from multiple concurrent writers.
383  * Returns 0 on success, an error code on failure.
384  */
385 int ima_parse_add_rule(char *rule)
386 {
387         const char *op = "update_policy";
388         struct ima_measure_rule_entry *entry;
389         int result = 0;
390         int audit_info = 0;
391
392         /* Prevent installed policy from changing */
393         if (ima_measure != &measure_default_rules) {
394                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
395                                     NULL, op, "already exists",
396                                     -EACCES, audit_info);
397                 return -EACCES;
398         }
399
400         entry = kzalloc(sizeof(*entry), GFP_KERNEL);
401         if (!entry) {
402                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
403                                     NULL, op, "-ENOMEM", -ENOMEM, audit_info);
404                 return -ENOMEM;
405         }
406
407         INIT_LIST_HEAD(&entry->list);
408
409         result = ima_parse_rule(rule, entry);
410         if (!result) {
411                 mutex_lock(&ima_measure_mutex);
412                 list_add_tail(&entry->list, &measure_policy_rules);
413                 mutex_unlock(&ima_measure_mutex);
414         } else {
415                 kfree(entry);
416                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
417                                     NULL, op, "invalid policy", result,
418                                     audit_info);
419         }
420         return result;
421 }
422
423 /* ima_delete_rules called to cleanup invalid policy */
424 void ima_delete_rules(void)
425 {
426         struct ima_measure_rule_entry *entry, *tmp;
427
428         mutex_lock(&ima_measure_mutex);
429         list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) {
430                 list_del(&entry->list);
431                 kfree(entry);
432         }
433         mutex_unlock(&ima_measure_mutex);
434 }