drm_auth.c

  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/export.h>
 32#include <linux/slab.h>
 33
 34#include <drm/drm_auth.h>
 35#include <drm/drm_drv.h>
 36#include <drm/drm_file.h>
 37#include <drm/drm_lease.h>
 38#include <drm/drm_print.h>
 39
 40#include "drm_internal.h"
 41
 42/**
 43 * DOC: master and authentication
 44 *
 45 * &struct drm_master is used to track groups of clients with open
 46 * primary 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
 64static 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 */
 82bool 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}
 92EXPORT_SYMBOL(drm_is_current_master);
 93
 94int 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	guard(mutex)(&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
108	drm_dbg_core(dev, "%u\n", auth->magic);
109
110	return ret < 0 ? ret : 0;
111}
112
113int drm_authmagic(struct drm_device *dev, void *data,
114		  struct drm_file *file_priv)
115{
116	struct drm_auth *auth = data;
117	struct drm_file *file;
118
119	drm_dbg_core(dev, "%u\n", auth->magic);
120
121	guard(mutex)(&dev->master_mutex);
122	file = idr_find(&file_priv->master->magic_map, auth->magic);
123	if (file) {
124		file->authenticated = 1;
125		idr_replace(&file_priv->master->magic_map, NULL, auth->magic);
126	}
127
128	return file ? 0 : -EINVAL;
129}
130
131struct drm_master *drm_master_create(struct drm_device *dev)
132{
133	struct drm_master *master;
134
135	master = kzalloc(sizeof(*master), GFP_KERNEL);
136	if (!master)
137		return NULL;
138
139	kref_init(&master->refcount);
140	idr_init_base(&master->magic_map, 1);
141	master->dev = dev;
142
143	/* initialize the tree of output resource lessees */
144	INIT_LIST_HEAD(&master->lessees);
145	INIT_LIST_HEAD(&master->lessee_list);
146	idr_init(&master->leases);
147	idr_init_base(&master->lessee_idr, 1);
148
149	return master;
150}
151
152static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv,
153			   bool new_master)
154{
155	dev->master = drm_master_get(fpriv->master);
156	if (dev->driver->master_set)
157		dev->driver->master_set(dev, fpriv, new_master);
158
159	fpriv->was_master = true;
160}
161
162static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
163{
164	struct drm_master *old_master;
165	struct drm_master *new_master;
166
167	lockdep_assert_held_once(&dev->master_mutex);
168
169	WARN_ON(fpriv->is_master);
170	old_master = fpriv->master;
171	new_master = drm_master_create(dev);
172	if (!new_master)
173		return -ENOMEM;
174	spin_lock(&fpriv->master_lookup_lock);
175	fpriv->master = new_master;
176	spin_unlock(&fpriv->master_lookup_lock);
177
178	fpriv->is_master = 1;
179	fpriv->authenticated = 1;
180
181	drm_set_master(dev, fpriv, true);
182
183	if (old_master)
184		drm_master_put(&old_master);
185
186	return 0;
187}
188
189/*
190 * In the olden days the SET/DROP_MASTER ioctls used to return EACCES when
191 * CAP_SYS_ADMIN was not set. This was used to prevent rogue applications
192 * from becoming master and/or failing to release it.
193 *
194 * At the same time, the first client (for a given VT) is _always_ master.
195 * Thus in order for the ioctls to succeed, one had to _explicitly_ run the
196 * application as root or flip the setuid bit.
197 *
198 * If the CAP_SYS_ADMIN was missing, no other client could become master...
199 * EVER :-( Leading to a) the graphics session dying badly or b) a completely
200 * locked session.
201 *
202 *
203 * As some point systemd-logind was introduced to orchestrate and delegate
204 * master as applicable. It does so by opening the fd and passing it to users
205 * while in itself logind a) does the set/drop master per users' request and
206 * b)  * implicitly drops master on VT switch.
207 *
208 * Even though logind looks like the future, there are a few issues:
209 *  - some platforms don't have equivalent (Android, CrOS, some BSDs) so
210 * root is required _solely_ for SET/DROP MASTER.
211 *  - applications may not be updated to use it,
212 *  - any client which fails to drop master* can DoS the application using
213 * logind, to a varying degree.
214 *
215 * * Either due missing CAP_SYS_ADMIN or simply not calling DROP_MASTER.
216 *
217 *
218 * Here we implement the next best thing:
219 *  - ensure the logind style of fd passing works unchanged, and
220 *  - allow a client to drop/set master, iff it is/was master at a given point
221 * in time.
222 *
223 * Note: DROP_MASTER cannot be free for all, as an arbitrator user could:
224 *  - DoS/crash the arbitrator - details would be implementation specific
225 *  - open the node, become master implicitly and cause issues
226 *
227 * As a result this fixes the following when using root-less build w/o logind
228 * - startx
229 * - weston
230 * - various compositors based on wlroots
231 */
232static int
233drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv)
234{
235	if (file_priv->was_master &&
236	    rcu_access_pointer(file_priv->pid) == task_tgid(current))
237		return 0;
238
239	if (!capable(CAP_SYS_ADMIN))
240		return -EACCES;
241
242	return 0;
243}
244
245int drm_setmaster_ioctl(struct drm_device *dev, void *data,
246			struct drm_file *file_priv)
247{
248	int ret;
249
250	guard(mutex)(&dev->master_mutex);
251
252	ret = drm_master_check_perm(dev, file_priv);
253	if (ret)
254		return ret;
255
256	if (drm_is_current_master_locked(file_priv))
257		return ret;
258
259	if (dev->master)
260		return -EBUSY;
261
262	if (!file_priv->master)
263		return -EINVAL;
264
265	if (!file_priv->is_master)
266		return drm_new_set_master(dev, file_priv);
267
268	if (file_priv->master->lessor != NULL) {
269		drm_dbg_lease(dev,
270			      "Attempt to set lessee %d as master\n",
271			      file_priv->master->lessee_id);
272		return -EINVAL;
273	}
274
275	drm_set_master(dev, file_priv, false);
276
277	return ret;
278}
279
280static void drm_drop_master(struct drm_device *dev,
281			    struct drm_file *fpriv)
282{
283	if (dev->driver->master_drop)
284		dev->driver->master_drop(dev, fpriv);
285	drm_master_put(&dev->master);
286}
287
288int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
289			 struct drm_file *file_priv)
290{
291	int ret;
292
293	guard(mutex)(&dev->master_mutex);
294
295	ret = drm_master_check_perm(dev, file_priv);
296	if (ret)
297		return ret;
298
299	if (!drm_is_current_master_locked(file_priv))
300		return -EINVAL;
301
302	if (!dev->master)
303		return -EINVAL;
304
305	if (file_priv->master->lessor != NULL) {
306		drm_dbg_lease(dev,
307			      "Attempt to drop lessee %d as master\n",
308			      file_priv->master->lessee_id);
309		return -EINVAL;
310	}
311
312	drm_drop_master(dev, file_priv);
313
314	return ret;
315}
316
317int drm_master_open(struct drm_file *file_priv)
318{
319	struct drm_device *dev = file_priv->minor->dev;
320	int ret = 0;
321
322	/* if there is no current master make this fd it, but do not create
323	 * any master object for render clients
324	 */
325	guard(mutex)(&dev->master_mutex);
326	if (!dev->master) {
327		ret = drm_new_set_master(dev, file_priv);
328	} else {
329		spin_lock(&file_priv->master_lookup_lock);
330		file_priv->master = drm_master_get(dev->master);
331		spin_unlock(&file_priv->master_lookup_lock);
332	}
333
334	return ret;
335}
336
337void drm_master_release(struct drm_file *file_priv)
338{
339	struct drm_device *dev = file_priv->minor->dev;
340	struct drm_master *master;
341
342	guard(mutex)(&dev->master_mutex);
343	master = file_priv->master;
344	if (file_priv->magic)
345		idr_remove(&file_priv->master->magic_map, file_priv->magic);
346
347	if (!drm_is_current_master_locked(file_priv))
348		goto out;
349
350	if (dev->master == file_priv->master)
351		drm_drop_master(dev, file_priv);
352out:
353	if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) {
354		/* Revoke any leases held by this or lessees, but only if
355		 * this is the "real" master
356		 */
357		drm_lease_revoke(master);
358	}
359
360	/* drop the master reference held by the file priv */
361	if (file_priv->master)
362		drm_master_put(&file_priv->master);
363}
364
365/**
366 * drm_master_get - reference a master pointer
367 * @master: &struct drm_master
368 *
369 * Increments the reference count of @master and returns a pointer to @master.
370 */
371struct drm_master *drm_master_get(struct drm_master *master)
372{
373	kref_get(&master->refcount);
374	return master;
375}
376EXPORT_SYMBOL(drm_master_get);
377
378/**
379 * drm_file_get_master - reference &drm_file.master of @file_priv
380 * @file_priv: DRM file private
381 *
382 * Increments the reference count of @file_priv's &drm_file.master and returns
383 * the &drm_file.master. If @file_priv has no &drm_file.master, returns NULL.
384 *
385 * Master pointers returned from this function should be unreferenced using
386 * drm_master_put().
387 */
388struct drm_master *drm_file_get_master(struct drm_file *file_priv)
389{
390	struct drm_master *master = NULL;
391
392	spin_lock(&file_priv->master_lookup_lock);
393	if (!file_priv->master)
394		goto unlock;
395	master = drm_master_get(file_priv->master);
396
397unlock:
398	spin_unlock(&file_priv->master_lookup_lock);
399	return master;
400}
401EXPORT_SYMBOL(drm_file_get_master);
402
403static void drm_master_destroy(struct kref *kref)
404{
405	struct drm_master *master = container_of(kref, struct drm_master, refcount);
406	struct drm_device *dev = master->dev;
407
408	if (drm_core_check_feature(dev, DRIVER_MODESET))
409		drm_lease_destroy(master);
410
411	idr_destroy(&master->magic_map);
412	idr_destroy(&master->leases);
413	idr_destroy(&master->lessee_idr);
414
415	kfree(master->unique);
416	kfree(master);
417}
418
419/**
420 * drm_master_put - unreference and clear a master pointer
421 * @master: pointer to a pointer of &struct drm_master
422 *
423 * This decrements the &drm_master behind @master and sets it to NULL.
424 */
425void drm_master_put(struct drm_master **master)
426{
427	kref_put(&(*master)->refcount, drm_master_destroy);
428	*master = NULL;
429}
430EXPORT_SYMBOL(drm_master_put);
431
432/* Used by drm_client and drm_fb_helper */
433bool drm_master_internal_acquire(struct drm_device *dev)
434{
435	mutex_lock(&dev->master_mutex);
436	if (dev->master) {
437		mutex_unlock(&dev->master_mutex);
438		return false;
439	}
440
441	return true;
442}
443EXPORT_SYMBOL(drm_master_internal_acquire);
444
445/* Used by drm_client and drm_fb_helper */
446void drm_master_internal_release(struct drm_device *dev)
447{
448	mutex_unlock(&dev->master_mutex);
449}
450EXPORT_SYMBOL(drm_master_internal_release);