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1/*
2 * Created: Tue Feb 2 08:37:54 1999 by [email protected]
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 <[email protected]>
9 * Author Gareth Hughes <[email protected]>
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_obj(*master);
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 && 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);