1 /*-
2 * Copyright (c) 2016, 2018 Robert N. M. Watson
3 * All rights reserved.
4 *
5 * This software was developed by BAE Systems, the University of Cambridge
6 * Computer Laboratory, and Memorial University under DARPA/AFRL contract
7 * FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent Computing
8 * (TC) research program.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 */
31
32 #include <sys/param.h>
33 #include <sys/conf.h>
34 #include <sys/ctype.h>
35 #include <sys/kernel.h>
36 #include <sys/malloc.h>
37 #include <sys/module.h>
38 #include <sys/queue.h>
39 #include <sys/refcount.h>
40
41 #include <sys/dtrace.h>
42 #include <sys/dtrace_bsd.h>
43
44 #include <bsm/audit.h>
45 #include <bsm/audit_internal.h>
46 #include <bsm/audit_kevents.h>
47
48 #include <security/audit/audit.h>
49 #include <security/audit/audit_private.h>
50
51 /*-
52 * Audit DTrace provider: allow DTrace to request that audit records be
53 * generated for various audit events, and then expose those records (in
54 * various forms) to probes. The model is that each event type has two
55 * probes, which use the event's name to create the probe:
56 *
57 * - "commit" passes the kernel-internal (unserialised) kaudit_record
58 * synchronously (from the originating thread) of the record as we prepare
59 * to "commit" the record to the audit queue.
60 *
61 * - "bsm" also passes generated BSM, and executes asynchronously in the audit
62 * worker thread, once it has been extracted from the audit queue. This is
63 * the point at which an audit record would be enqueued to the trail on
64 * disk, or to pipes.
65 *
66 * These probes support very different goals. The former executes in the
67 * thread originating the record, making it easier to correlate other DTrace
68 * probe activity with the event described in the record. The latter gives
69 * access to BSM-formatted events (at a cost) allowing DTrace to extract BSM
70 * directly an alternative mechanism to the formal audit trail and audit
71 * pipes.
72 *
73 * To generate names for numeric event IDs, userspace will push the contents
74 * of /etc/security/audit_event into the kernel during audit setup, much as it
75 * does /etc/security/audit_class. We then create the probes for each of
76 * those mappings. If one (or both) of the probes are enabled, then we cause
77 * a record to be generated (as both normal audit preselection and audit pipes
78 * do), and catch it on the way out during commit. There are suitable hook
79 * functions in the audit code that this provider can register to catch
80 * various events in the audit-record life cycle.
81 *
82 * Further ponderings:
83 *
84 * - How do we want to handle events for which there are not names -- perhaps
85 * a catch-all probe for those events without mappings?
86 *
87 * - Should the evname code really be present even if DTrace isn't loaded...?
88 * Right now, we arrange that it is so that userspace can usefully maintain
89 * the list in case DTrace is later loaded (and to prevent userspace
90 * confusion).
91 *
92 * - Should we add an additional set of audit:class::commit probes that use
93 * event class names to match broader categories of events as specified in
94 * /etc/security/event_class?
95 *
96 * - If we pursue that last point, we will want to pass the name of the event
97 * into the probe explicitly (e.g., as arg0), since it would no longer be
98 * available as the probe function name.
99 */
100
101 static int dtaudit_unload(void);
102 static void dtaudit_getargdesc(void *, dtrace_id_t, void *,
103 dtrace_argdesc_t *);
104 static void dtaudit_provide(void *, dtrace_probedesc_t *);
105 static void dtaudit_destroy(void *, dtrace_id_t, void *);
106 static void dtaudit_enable(void *, dtrace_id_t, void *);
107 static void dtaudit_disable(void *, dtrace_id_t, void *);
108 static void dtaudit_load(void *);
109
110 static dtrace_pattr_t dtaudit_attr = {
111 { DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_COMMON },
112 { DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
113 { DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
114 { DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_COMMON },
115 { DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_COMMON },
116 };
117
118 /*
119 * Strings for the "module" and "name" portions of the probe. The name of the
120 * audit event will be the "function" portion of the probe. All dtaudit
121 * probes therefore take the form audit:event:<event name>:commit.
122 */
123 static char *dtaudit_module_str = "event";
124 static char *dtaudit_name_commit_str = "commit";
125 static char *dtaudit_name_bsm_str = "bsm";
126
127 static dtrace_pops_t dtaudit_pops = {
128 .dtps_provide = dtaudit_provide,
129 .dtps_provide_module = NULL,
130 .dtps_enable = dtaudit_enable,
131 .dtps_disable = dtaudit_disable,
132 .dtps_suspend = NULL,
133 .dtps_resume = NULL,
134 .dtps_getargdesc = dtaudit_getargdesc,
135 .dtps_getargval = NULL,
136 .dtps_usermode = NULL,
137 .dtps_destroy = dtaudit_destroy
138 };
139
140 static dtrace_provider_id_t dtaudit_id;
141
142 /*
143 * Because looking up entries in the event-to-name mapping is quite expensive,
144 * maintain a global flag tracking whether any dtaudit probes are enabled. If
145 * not, don't bother doing all that work whenever potential queries about
146 * events turn up during preselection or commit.
147 *
148 * NB: We used to maintain our own variable in dtaudit, but now use the
149 * centralized audit_dtrace_enabled variable imported from the audit code.
150 *
151 * static uint_t dtaudit_probes_enabled;
152 */
153
154 /*
155 * Check dtaudit policy for the event to see whether this is an event we would
156 * like to preselect (i.e., cause an audit record to be generated for). To
157 * minimise probe effect when not used at all, we not only check for the probe
158 * on the individual event, but also a global flag indicating that at least
159 * one probe is enabled, before acquiring locks, searching lists, etc.
160 *
161 * If the event is selected, return an evname_elem reference to be stored in
162 * the audit record, which we can use later to avoid further lookups. The
163 * contents of the evname_elem must be sufficiently stable so as to not risk
164 * race conditions here.
165 *
166 * Currently, we take an interest only in the 'event' argument, but in the
167 * future might want to support other types of record selection tied to
168 * additional probe types (e.g., event clases).
169 *
170 * XXXRW: Should we have a catch-all probe here for events without registered
171 * names?
172 */
173 static void *
dtaudit_preselect(au_id_t auid,au_event_t event,au_class_t class)174 dtaudit_preselect(au_id_t auid, au_event_t event, au_class_t class)
175 {
176 struct evname_elem *ene;
177 int probe_enabled;
178
179 /*
180 * NB: Lockless reads here may return a slightly stale value; this is
181 * considered better than acquiring a lock, however.
182 */
183 if (!audit_dtrace_enabled)
184 return (NULL);
185 ene = au_evnamemap_lookup(event);
186 if (ene == NULL)
187 return (NULL);
188
189 /*
190 * See if either of the two probes for the audit event are enabled.
191 *
192 * NB: Lock also not acquired here -- but perhaps it wouldn't matter
193 * given that we've already used the list lock above?
194 *
195 * XXXRW: Alternatively, au_evnamemap_lookup() could return these
196 * values while holding the list lock...?
197 */
198 probe_enabled = ene->ene_commit_probe_enabled ||
199 ene->ene_bsm_probe_enabled;
200 if (!probe_enabled)
201 return (NULL);
202 return ((void *)ene);
203 }
204
205 /*
206 * Commit probe pre-BSM. Fires the probe but also checks to see if we should
207 * ask the audit framework to call us again with BSM arguments in the audit
208 * worker thread.
209 *
210 * XXXRW: Should we have a catch-all probe here for events without registered
211 * names?
212 */
213 static int
dtaudit_commit(struct kaudit_record * kar,au_id_t auid,au_event_t event,au_class_t class,int sorf)214 dtaudit_commit(struct kaudit_record *kar, au_id_t auid, au_event_t event,
215 au_class_t class, int sorf)
216 {
217 char ene_name_lower[EVNAMEMAP_NAME_SIZE];
218 struct evname_elem *ene;
219 int i;
220
221 ene = (struct evname_elem *)kar->k_dtaudit_state;
222 if (ene == NULL)
223 return (0);
224
225 /*
226 * Process a possibly registered commit probe.
227 */
228 if (ene->ene_commit_probe_enabled) {
229 /*
230 * XXXRW: Lock ene to provide stability to the name string. A
231 * bit undesirable! We may want another locking strategy
232 * here. At least we don't run the DTrace probe under the
233 * lock.
234 *
235 * XXXRW: We provide the struct audit_record pointer -- but
236 * perhaps should provide the kaudit_record pointer?
237 */
238 EVNAME_LOCK(ene);
239 for (i = 0; i < sizeof(ene_name_lower); i++)
240 ene_name_lower[i] = tolower(ene->ene_name[i]);
241 EVNAME_UNLOCK(ene);
242 dtrace_probe(ene->ene_commit_probe_id,
243 (uintptr_t)ene_name_lower, (uintptr_t)&kar->k_ar, 0, 0, 0);
244 }
245
246 /*
247 * Return the state of the BSM probe to the caller.
248 */
249 return (ene->ene_bsm_probe_enabled);
250 }
251
252 /*
253 * Commit probe post-BSM.
254 *
255 * XXXRW: Should we have a catch-all probe here for events without registered
256 * names?
257 */
258 static void
dtaudit_bsm(struct kaudit_record * kar,au_id_t auid,au_event_t event,au_class_t class,int sorf,void * bsm_data,size_t bsm_len)259 dtaudit_bsm(struct kaudit_record *kar, au_id_t auid, au_event_t event,
260 au_class_t class, int sorf, void *bsm_data, size_t bsm_len)
261 {
262 char ene_name_lower[EVNAMEMAP_NAME_SIZE];
263 struct evname_elem *ene;
264 int i;
265
266 ene = (struct evname_elem *)kar->k_dtaudit_state;
267 if (ene == NULL)
268 return;
269 if (!(ene->ene_bsm_probe_enabled))
270 return;
271
272 /*
273 * XXXRW: Lock ene to provide stability to the name string. A bit
274 * undesirable! We may want another locking strategy here. At least
275 * we don't run the DTrace probe under the lock.
276 *
277 * XXXRW: We provide the struct audit_record pointer -- but perhaps
278 * should provide the kaudit_record pointer?
279 */
280 EVNAME_LOCK(ene);
281 for (i = 0; i < sizeof(ene_name_lower); i++)
282 ene_name_lower[i] = tolower(ene->ene_name[i]);
283 EVNAME_UNLOCK(ene);
284 dtrace_probe(ene->ene_bsm_probe_id, (uintptr_t)ene_name_lower,
285 (uintptr_t)&kar->k_ar, (uintptr_t)bsm_data, (uintptr_t)bsm_len,
286 0);
287 }
288
289 /*
290 * A very simple provider: argument types are identical across all probes: the
291 * kaudit_record, plus a BSM pointer and length.
292 */
293 static void
dtaudit_getargdesc(void * arg,dtrace_id_t id,void * parg,dtrace_argdesc_t * desc)294 dtaudit_getargdesc(void *arg, dtrace_id_t id, void *parg,
295 dtrace_argdesc_t *desc)
296 {
297 struct evname_elem *ene;
298 const char *p;
299
300 ene = (struct evname_elem *)parg;
301 p = NULL;
302 switch (desc->dtargd_ndx) {
303 case 0:
304 /* Audit event name. */
305 p = "char *";
306 break;
307
308 case 1:
309 /* In-kernel audit record. */
310 p = "struct audit_record *";
311 break;
312
313 case 2:
314 /* BSM data, if present. */
315 if (id == ene->ene_bsm_probe_id)
316 p = "const void *";
317 else
318 desc->dtargd_ndx = DTRACE_ARGNONE;
319 break;
320
321 case 3:
322 /* BSM length, if present. */
323 if (id == ene->ene_bsm_probe_id)
324 p = "size_t";
325 else
326 desc->dtargd_ndx = DTRACE_ARGNONE;
327 break;
328
329 default:
330 desc->dtargd_ndx = DTRACE_ARGNONE;
331 break;
332 }
333 if (p != NULL)
334 strlcpy(desc->dtargd_native, p, sizeof(desc->dtargd_native));
335 }
336
337 /*
338 * Callback from the event-to-name mapping code when performing
339 * evname_foreach(). Note that we may update the entry, so the foreach code
340 * must have a write lock. However, as the synchronisation model is private
341 * to the evname code, we cannot easily assert it here.
342 *
343 * XXXRW: How do we want to handle event rename / collision issues here --
344 * e.g., if userspace was using a name to point to one event number, and then
345 * changes it so that the name points at another? For now, paper over this by
346 * skipping event numbers that are already registered, and likewise skipping
347 * names that are already registered. However, this could lead to confusing
348 * behaviour so possibly needs to be resolved in the longer term.
349 */
350 static void
dtaudit_au_evnamemap_callback(struct evname_elem * ene)351 dtaudit_au_evnamemap_callback(struct evname_elem *ene)
352 {
353 char ene_name_lower[EVNAMEMAP_NAME_SIZE];
354 int i;
355
356 /*
357 * DTrace, by convention, has lower-case probe names. However, the
358 * in-kernel event-to-name mapping table must maintain event-name case
359 * as submitted by userspace. Create a temporary lower-case version
360 * here, away from the fast path, to use when exposing the event name
361 * to DTrace as part of the name of a probe.
362 *
363 * NB: Convert the entire array, including the terminating nul,
364 * because these strings are short and it's more work not to. If they
365 * become long, we might feel more guilty about this sloppiness!
366 */
367 for (i = 0; i < sizeof(ene_name_lower); i++)
368 ene_name_lower[i] = tolower(ene->ene_name[i]);
369
370 /*
371 * Don't register a new probe if this event number already has an
372 * associated commit probe -- or if another event has already
373 * registered this name.
374 *
375 * XXXRW: There is an argument that if multiple numeric events match
376 * a single name, they should all be exposed to the same named probe.
377 * In particular, we should perhaps use a probe ID returned by this
378 * lookup and just stick that in the saved probe ID?
379 */
380 if ((ene->ene_commit_probe_id == 0) &&
381 (dtrace_probe_lookup(dtaudit_id, dtaudit_module_str,
382 ene_name_lower, dtaudit_name_commit_str) == 0)) {
383 /*
384 * Create the commit probe.
385 *
386 * NB: We don't declare any extra stack frames because stack()
387 * will just return the path to the audit commit code, which
388 * is not really interesting anyway.
389 *
390 * We pass in the pointer to the evnam_elem entry so that we
391 * can easily change its enabled flag in the probe
392 * enable/disable interface.
393 */
394 ene->ene_commit_probe_id = dtrace_probe_create(dtaudit_id,
395 dtaudit_module_str, ene_name_lower,
396 dtaudit_name_commit_str, 0, ene);
397 }
398
399 /*
400 * Don't register a new probe if this event number already has an
401 * associated bsm probe -- or if another event has already
402 * registered this name.
403 *
404 * XXXRW: There is an argument that if multiple numeric events match
405 * a single name, they should all be exposed to the same named probe.
406 * In particular, we should perhaps use a probe ID returned by this
407 * lookup and just stick that in the saved probe ID?
408 */
409 if ((ene->ene_bsm_probe_id == 0) &&
410 (dtrace_probe_lookup(dtaudit_id, dtaudit_module_str,
411 ene_name_lower, dtaudit_name_bsm_str) == 0)) {
412 /*
413 * Create the bsm probe.
414 *
415 * NB: We don't declare any extra stack frames because stack()
416 * will just return the path to the audit commit code, which
417 * is not really interesting anyway.
418 *
419 * We pass in the pointer to the evnam_elem entry so that we
420 * can easily change its enabled flag in the probe
421 * enable/disable interface.
422 */
423 ene->ene_bsm_probe_id = dtrace_probe_create(dtaudit_id,
424 dtaudit_module_str, ene_name_lower, dtaudit_name_bsm_str,
425 0, ene);
426 }
427 }
428
429 static void
dtaudit_provide(void * arg,dtrace_probedesc_t * desc)430 dtaudit_provide(void *arg, dtrace_probedesc_t *desc)
431 {
432
433 /*
434 * Walk all registered number-to-name mapping entries, and ensure each
435 * is properly registered.
436 */
437 au_evnamemap_foreach(dtaudit_au_evnamemap_callback);
438 }
439
440 static void
dtaudit_destroy(void * arg,dtrace_id_t id,void * parg)441 dtaudit_destroy(void *arg, dtrace_id_t id, void *parg)
442 {
443 }
444
445 static void
dtaudit_enable(void * arg,dtrace_id_t id,void * parg)446 dtaudit_enable(void *arg, dtrace_id_t id, void *parg)
447 {
448 struct evname_elem *ene;
449
450 ene = parg;
451 KASSERT(ene->ene_commit_probe_id == id || ene->ene_bsm_probe_id == id,
452 ("%s: probe ID mismatch (%u, %u != %u)", __func__,
453 ene->ene_commit_probe_id, ene->ene_bsm_probe_id, id));
454
455 if (id == ene->ene_commit_probe_id)
456 ene->ene_commit_probe_enabled = 1;
457 else
458 ene->ene_bsm_probe_enabled = 1;
459 refcount_acquire(&audit_dtrace_enabled);
460 audit_syscalls_enabled_update();
461 }
462
463 static void
dtaudit_disable(void * arg,dtrace_id_t id,void * parg)464 dtaudit_disable(void *arg, dtrace_id_t id, void *parg)
465 {
466 struct evname_elem *ene;
467
468 ene = parg;
469 KASSERT(ene->ene_commit_probe_id == id || ene->ene_bsm_probe_id == id,
470 ("%s: probe ID mismatch (%u, %u != %u)", __func__,
471 ene->ene_commit_probe_id, ene->ene_bsm_probe_id, id));
472
473 if (id == ene->ene_commit_probe_id)
474 ene->ene_commit_probe_enabled = 0;
475 else
476 ene->ene_bsm_probe_enabled = 0;
477 (void)refcount_release(&audit_dtrace_enabled);
478 audit_syscalls_enabled_update();
479 }
480
481 static void
dtaudit_load(void * dummy)482 dtaudit_load(void *dummy)
483 {
484
485 if (dtrace_register("audit", &dtaudit_attr, DTRACE_PRIV_USER, NULL,
486 &dtaudit_pops, NULL, &dtaudit_id) != 0)
487 return;
488 dtaudit_hook_preselect = dtaudit_preselect;
489 dtaudit_hook_commit = dtaudit_commit;
490 dtaudit_hook_bsm = dtaudit_bsm;
491 }
492
493 static int
dtaudit_unload(void)494 dtaudit_unload(void)
495 {
496 int error;
497
498 dtaudit_hook_preselect = NULL;
499 dtaudit_hook_commit = NULL;
500 dtaudit_hook_bsm = NULL;
501 if ((error = dtrace_unregister(dtaudit_id)) != 0)
502 return (error);
503 return (0);
504 }
505
506 static int
dtaudit_modevent(module_t mod __unused,int type,void * data __unused)507 dtaudit_modevent(module_t mod __unused, int type, void *data __unused)
508 {
509 int error = 0;
510
511 switch (type) {
512 case MOD_LOAD:
513 case MOD_UNLOAD:
514 case MOD_SHUTDOWN:
515 break;
516
517 default:
518 error = EOPNOTSUPP;
519 break;
520 }
521
522 return (error);
523 }
524
525 SYSINIT(dtaudit_load, SI_SUB_DTRACE_PROVIDER, SI_ORDER_ANY, dtaudit_load,
526 NULL);
527 SYSUNINIT(dtaudit_unload, SI_SUB_DTRACE_PROVIDER, SI_ORDER_ANY,
528 dtaudit_unload, NULL);
529
530 DEV_MODULE(dtaudit, dtaudit_modevent, NULL);
531 MODULE_VERSION(dtaudit, 1);
532 MODULE_DEPEND(dtaudit, dtrace, 1, 1, 1);
533 MODULE_DEPEND(dtaudit, opensolaris, 1, 1, 1);
534