1 /*
2  * Created: Tue Feb  2 08:37:54 1999 by faith@valinux.com
3  *
4  * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
5  * Copyright 2000 VA Linux Systems, Inc., Sunnyvale, California.
6  * All Rights Reserved.
7  *
8  * Author Rickard E. (Rik) Faith <faith@valinux.com>
9  * Author Gareth Hughes <gareth@valinux.com>
10  *
11  * Permission is hereby granted, free of charge, to any person obtaining a
12  * copy of this software and associated documentation files (the "Software"),
13  * to deal in the Software without restriction, including without limitation
14  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
15  * and/or sell copies of the Software, and to permit persons to whom the
16  * Software is furnished to do so, subject to the following conditions:
17  *
18  * The above copyright notice and this permission notice (including the next
19  * paragraph) shall be included in all copies or substantial portions of the
20  * Software.
21  *
22  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
23  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
24  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
25  * VA LINUX SYSTEMS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
26  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
27  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
28  * OTHER DEALINGS IN THE SOFTWARE.
29  */
30 
31 #include <linux/slab.h>
32 
33 #include <drm/drm_auth.h>
34 #include <drm/drm_drv.h>
35 #include <drm/drm_file.h>
36 #include <drm/drm_lease.h>
37 #include <drm/drm_print.h>
38 
39 #include "drm_internal.h"
40 #include "drm_legacy.h"
41 
42 /**
43  * DOC: master and authentication
44  *
45  * &struct drm_master is used to track groups of clients with open
46  * primary/legacy device nodes. For every &struct drm_file which has had at
47  * least once successfully became the device master (either through the
48  * SET_MASTER IOCTL, or implicitly through opening the primary device node when
49  * no one else is the current master that time) there exists one &drm_master.
50  * This is noted in &drm_file.is_master. All other clients have just a pointer
51  * to the &drm_master they are associated with.
52  *
53  * In addition only one &drm_master can be the current master for a &drm_device.
54  * It can be switched through the DROP_MASTER and SET_MASTER IOCTL, or
55  * implicitly through closing/opening the primary device node. See also
56  * drm_is_current_master().
57  *
58  * Clients can authenticate against the current master (if it matches their own)
59  * using the GETMAGIC and AUTHMAGIC IOCTLs. Together with exchanging masters,
60  * this allows controlled access to the device for an entire group of mutually
61  * trusted clients.
62  */
63 
drm_is_current_master_locked(struct drm_file * fpriv)64 static bool drm_is_current_master_locked(struct drm_file *fpriv)
65 {
66 	lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) ||
67 			    lockdep_is_held(&fpriv->minor->dev->master_mutex));
68 
69 	return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
70 }
71 
72 /**
73  * drm_is_current_master - checks whether @priv is the current master
74  * @fpriv: DRM file private
75  *
76  * Checks whether @fpriv is current master on its device. This decides whether a
77  * client is allowed to run DRM_MASTER IOCTLs.
78  *
79  * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting
80  * - the current master is assumed to own the non-shareable display hardware.
81  */
drm_is_current_master(struct drm_file * fpriv)82 bool drm_is_current_master(struct drm_file *fpriv)
83 {
84 	bool ret;
85 
86 	spin_lock(&fpriv->master_lookup_lock);
87 	ret = drm_is_current_master_locked(fpriv);
88 	spin_unlock(&fpriv->master_lookup_lock);
89 
90 	return ret;
91 }
92 EXPORT_SYMBOL(drm_is_current_master);
93 
drm_getmagic(struct drm_device * dev,void * data,struct drm_file * file_priv)94 int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
95 {
96 	struct drm_auth *auth = data;
97 	int ret = 0;
98 
99 	mutex_lock(&dev->master_mutex);
100 	if (!file_priv->magic) {
101 		ret = idr_alloc(&file_priv->master->magic_map, file_priv,
102 				1, 0, GFP_KERNEL);
103 		if (ret >= 0)
104 			file_priv->magic = ret;
105 	}
106 	auth->magic = file_priv->magic;
107 	mutex_unlock(&dev->master_mutex);
108 
109 	drm_dbg_core(dev, "%u\n", auth->magic);
110 
111 	return ret < 0 ? ret : 0;
112 }
113 
drm_authmagic(struct drm_device * dev,void * data,struct drm_file * file_priv)114 int drm_authmagic(struct drm_device *dev, void *data,
115 		  struct drm_file *file_priv)
116 {
117 	struct drm_auth *auth = data;
118 	struct drm_file *file;
119 
120 	drm_dbg_core(dev, "%u\n", auth->magic);
121 
122 	mutex_lock(&dev->master_mutex);
123 	file = idr_find(&file_priv->master->magic_map, auth->magic);
124 	if (file) {
125 		file->authenticated = 1;
126 		idr_replace(&file_priv->master->magic_map, NULL, auth->magic);
127 	}
128 	mutex_unlock(&dev->master_mutex);
129 
130 	return file ? 0 : -EINVAL;
131 }
132 
drm_master_create(struct drm_device * dev)133 struct drm_master *drm_master_create(struct drm_device *dev)
134 {
135 	struct drm_master *master;
136 
137 	master = kzalloc(sizeof(*master), GFP_KERNEL);
138 	if (!master)
139 		return NULL;
140 
141 	kref_init(&master->refcount);
142 	drm_master_legacy_init(master);
143 	idr_init_base(&master->magic_map, 1);
144 	master->dev = dev;
145 
146 	/* initialize the tree of output resource lessees */
147 	INIT_LIST_HEAD(&master->lessees);
148 	INIT_LIST_HEAD(&master->lessee_list);
149 	idr_init(&master->leases);
150 	idr_init_base(&master->lessee_idr, 1);
151 
152 	return master;
153 }
154 
drm_set_master(struct drm_device * dev,struct drm_file * fpriv,bool new_master)155 static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv,
156 			   bool new_master)
157 {
158 	dev->master = drm_master_get(fpriv->master);
159 	if (dev->driver->master_set)
160 		dev->driver->master_set(dev, fpriv, new_master);
161 
162 	fpriv->was_master = true;
163 }
164 
drm_new_set_master(struct drm_device * dev,struct drm_file * fpriv)165 static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
166 {
167 	struct drm_master *old_master;
168 	struct drm_master *new_master;
169 
170 	lockdep_assert_held_once(&dev->master_mutex);
171 
172 	WARN_ON(fpriv->is_master);
173 	old_master = fpriv->master;
174 	new_master = drm_master_create(dev);
175 	if (!new_master)
176 		return -ENOMEM;
177 	spin_lock(&fpriv->master_lookup_lock);
178 	fpriv->master = new_master;
179 	spin_unlock(&fpriv->master_lookup_lock);
180 
181 	fpriv->is_master = 1;
182 	fpriv->authenticated = 1;
183 
184 	drm_set_master(dev, fpriv, true);
185 
186 	if (old_master)
187 		drm_master_put(&old_master);
188 
189 	return 0;
190 }
191 
192 /*
193  * In the olden days the SET/DROP_MASTER ioctls used to return EACCES when
194  * CAP_SYS_ADMIN was not set. This was used to prevent rogue applications
195  * from becoming master and/or failing to release it.
196  *
197  * At the same time, the first client (for a given VT) is _always_ master.
198  * Thus in order for the ioctls to succeed, one had to _explicitly_ run the
199  * application as root or flip the setuid bit.
200  *
201  * If the CAP_SYS_ADMIN was missing, no other client could become master...
202  * EVER :-( Leading to a) the graphics session dying badly or b) a completely
203  * locked session.
204  *
205  *
206  * As some point systemd-logind was introduced to orchestrate and delegate
207  * master as applicable. It does so by opening the fd and passing it to users
208  * while in itself logind a) does the set/drop master per users' request and
209  * b)  * implicitly drops master on VT switch.
210  *
211  * Even though logind looks like the future, there are a few issues:
212  *  - some platforms don't have equivalent (Android, CrOS, some BSDs) so
213  * root is required _solely_ for SET/DROP MASTER.
214  *  - applications may not be updated to use it,
215  *  - any client which fails to drop master* can DoS the application using
216  * logind, to a varying degree.
217  *
218  * * Either due missing CAP_SYS_ADMIN or simply not calling DROP_MASTER.
219  *
220  *
221  * Here we implement the next best thing:
222  *  - ensure the logind style of fd passing works unchanged, and
223  *  - allow a client to drop/set master, iff it is/was master at a given point
224  * in time.
225  *
226  * Note: DROP_MASTER cannot be free for all, as an arbitrator user could:
227  *  - DoS/crash the arbitrator - details would be implementation specific
228  *  - open the node, become master implicitly and cause issues
229  *
230  * As a result this fixes the following when using root-less build w/o logind
231  * - startx
232  * - weston
233  * - various compositors based on wlroots
234  */
235 static int
drm_master_check_perm(struct drm_device * dev,struct drm_file * file_priv)236 drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv)
237 {
238 	if (file_priv->pid == task_pid(current) && file_priv->was_master)
239 		return 0;
240 
241 	if (!capable(CAP_SYS_ADMIN))
242 		return -EACCES;
243 
244 	return 0;
245 }
246 
drm_setmaster_ioctl(struct drm_device * dev,void * data,struct drm_file * file_priv)247 int drm_setmaster_ioctl(struct drm_device *dev, void *data,
248 			struct drm_file *file_priv)
249 {
250 	int ret;
251 
252 	mutex_lock(&dev->master_mutex);
253 
254 	ret = drm_master_check_perm(dev, file_priv);
255 	if (ret)
256 		goto out_unlock;
257 
258 	if (drm_is_current_master_locked(file_priv))
259 		goto out_unlock;
260 
261 	if (dev->master) {
262 		ret = -EBUSY;
263 		goto out_unlock;
264 	}
265 
266 	if (!file_priv->master) {
267 		ret = -EINVAL;
268 		goto out_unlock;
269 	}
270 
271 	if (!file_priv->is_master) {
272 		ret = drm_new_set_master(dev, file_priv);
273 		goto out_unlock;
274 	}
275 
276 	if (file_priv->master->lessor != NULL) {
277 		drm_dbg_lease(dev,
278 			      "Attempt to set lessee %d as master\n",
279 			      file_priv->master->lessee_id);
280 		ret = -EINVAL;
281 		goto out_unlock;
282 	}
283 
284 	drm_set_master(dev, file_priv, false);
285 out_unlock:
286 	mutex_unlock(&dev->master_mutex);
287 	return ret;
288 }
289 
drm_drop_master(struct drm_device * dev,struct drm_file * fpriv)290 static void drm_drop_master(struct drm_device *dev,
291 			    struct drm_file *fpriv)
292 {
293 	if (dev->driver->master_drop)
294 		dev->driver->master_drop(dev, fpriv);
295 	drm_master_put(&dev->master);
296 }
297 
drm_dropmaster_ioctl(struct drm_device * dev,void * data,struct drm_file * file_priv)298 int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
299 			 struct drm_file *file_priv)
300 {
301 	int ret;
302 
303 	mutex_lock(&dev->master_mutex);
304 
305 	ret = drm_master_check_perm(dev, file_priv);
306 	if (ret)
307 		goto out_unlock;
308 
309 	if (!drm_is_current_master_locked(file_priv)) {
310 		ret = -EINVAL;
311 		goto out_unlock;
312 	}
313 
314 	if (!dev->master) {
315 		ret = -EINVAL;
316 		goto out_unlock;
317 	}
318 
319 	if (file_priv->master->lessor != NULL) {
320 		drm_dbg_lease(dev,
321 			      "Attempt to drop lessee %d as master\n",
322 			      file_priv->master->lessee_id);
323 		ret = -EINVAL;
324 		goto out_unlock;
325 	}
326 
327 	drm_drop_master(dev, file_priv);
328 out_unlock:
329 	mutex_unlock(&dev->master_mutex);
330 	return ret;
331 }
332 
drm_master_open(struct drm_file * file_priv)333 int drm_master_open(struct drm_file *file_priv)
334 {
335 	struct drm_device *dev = file_priv->minor->dev;
336 	int ret = 0;
337 
338 	/* if there is no current master make this fd it, but do not create
339 	 * any master object for render clients
340 	 */
341 	mutex_lock(&dev->master_mutex);
342 	if (!dev->master) {
343 		ret = drm_new_set_master(dev, file_priv);
344 	} else {
345 		spin_lock(&file_priv->master_lookup_lock);
346 		file_priv->master = drm_master_get(dev->master);
347 		spin_unlock(&file_priv->master_lookup_lock);
348 	}
349 	mutex_unlock(&dev->master_mutex);
350 
351 	return ret;
352 }
353 
drm_master_release(struct drm_file * file_priv)354 void drm_master_release(struct drm_file *file_priv)
355 {
356 	struct drm_device *dev = file_priv->minor->dev;
357 	struct drm_master *master;
358 
359 	mutex_lock(&dev->master_mutex);
360 	master = file_priv->master;
361 	if (file_priv->magic)
362 		idr_remove(&file_priv->master->magic_map, file_priv->magic);
363 
364 	if (!drm_is_current_master_locked(file_priv))
365 		goto out;
366 
367 	drm_legacy_lock_master_cleanup(dev, master);
368 
369 	if (dev->master == file_priv->master)
370 		drm_drop_master(dev, file_priv);
371 out:
372 	if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) {
373 		/* Revoke any leases held by this or lessees, but only if
374 		 * this is the "real" master
375 		 */
376 		drm_lease_revoke(master);
377 	}
378 
379 	/* drop the master reference held by the file priv */
380 	if (file_priv->master)
381 		drm_master_put(&file_priv->master);
382 	mutex_unlock(&dev->master_mutex);
383 }
384 
385 /**
386  * drm_master_get - reference a master pointer
387  * @master: &struct drm_master
388  *
389  * Increments the reference count of @master and returns a pointer to @master.
390  */
drm_master_get(struct drm_master * master)391 struct drm_master *drm_master_get(struct drm_master *master)
392 {
393 	kref_get(&master->refcount);
394 	return master;
395 }
396 EXPORT_SYMBOL(drm_master_get);
397 
398 /**
399  * drm_file_get_master - reference &drm_file.master of @file_priv
400  * @file_priv: DRM file private
401  *
402  * Increments the reference count of @file_priv's &drm_file.master and returns
403  * the &drm_file.master. If @file_priv has no &drm_file.master, returns NULL.
404  *
405  * Master pointers returned from this function should be unreferenced using
406  * drm_master_put().
407  */
drm_file_get_master(struct drm_file * file_priv)408 struct drm_master *drm_file_get_master(struct drm_file *file_priv)
409 {
410 	struct drm_master *master = NULL;
411 
412 	spin_lock(&file_priv->master_lookup_lock);
413 	if (!file_priv->master)
414 		goto unlock;
415 	master = drm_master_get(file_priv->master);
416 
417 unlock:
418 	spin_unlock(&file_priv->master_lookup_lock);
419 	return master;
420 }
421 EXPORT_SYMBOL(drm_file_get_master);
422 
drm_master_destroy(struct kref * kref)423 static void drm_master_destroy(struct kref *kref)
424 {
425 	struct drm_master *master = container_of(kref, struct drm_master, refcount);
426 	struct drm_device *dev = master->dev;
427 
428 	if (drm_core_check_feature(dev, DRIVER_MODESET))
429 		drm_lease_destroy(master);
430 
431 	drm_legacy_master_rmmaps(dev, master);
432 
433 	idr_destroy(&master->magic_map);
434 	idr_destroy(&master->leases);
435 	idr_destroy(&master->lessee_idr);
436 
437 	kfree(master->unique);
438 	kfree(master);
439 }
440 
441 /**
442  * drm_master_put - unreference and clear a master pointer
443  * @master: pointer to a pointer of &struct drm_master
444  *
445  * This decrements the &drm_master behind @master and sets it to NULL.
446  */
drm_master_put(struct drm_master ** master)447 void drm_master_put(struct drm_master **master)
448 {
449 	kref_put(&(*master)->refcount, drm_master_destroy);
450 	*master = NULL;
451 }
452 EXPORT_SYMBOL(drm_master_put);
453 
454 /* Used by drm_client and drm_fb_helper */
drm_master_internal_acquire(struct drm_device * dev)455 bool drm_master_internal_acquire(struct drm_device *dev)
456 {
457 	mutex_lock(&dev->master_mutex);
458 	if (dev->master) {
459 		mutex_unlock(&dev->master_mutex);
460 		return false;
461 	}
462 
463 	return true;
464 }
465 EXPORT_SYMBOL(drm_master_internal_acquire);
466 
467 /* Used by drm_client and drm_fb_helper */
drm_master_internal_release(struct drm_device * dev)468 void drm_master_internal_release(struct drm_device *dev)
469 {
470 	mutex_unlock(&dev->master_mutex);
471 }
472 EXPORT_SYMBOL(drm_master_internal_release);
473