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
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(master: 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(lock: &fpriv->master_lookup_lock);
87 ret = drm_is_current_master_locked(fpriv);
88 spin_unlock(lock: &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 mutex_lock(&dev->master_mutex);
100 if (!file_priv->magic) {
101 ret = idr_alloc(&file_priv->master->magic_map, ptr: file_priv,
102 start: 1, end: 0, GFP_KERNEL);
103 if (ret >= 0)
104 file_priv->magic = ret;
105 }
106 auth->magic = file_priv->magic;
107 mutex_unlock(lock: &dev->master_mutex);
108
109 drm_dbg_core(dev, "%u\n", auth->magic);
110
111 return ret < 0 ? ret : 0;
112}
113
114int 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, id: auth->magic);
124 if (file) {
125 file->authenticated = 1;
126 idr_replace(&file_priv->master->magic_map, NULL, id: auth->magic);
127 }
128 mutex_unlock(lock: &dev->master_mutex);
129
130 return file ? 0 : -EINVAL;
131}
132
133struct drm_master *drm_master_create(struct drm_device *dev)
134{
135 struct drm_master *master;
136
137 master = kzalloc(size: sizeof(*master), GFP_KERNEL);
138 if (!master)
139 return NULL;
140
141 kref_init(kref: &master->refcount);
142 drm_master_legacy_init(master);
143 idr_init_base(idr: &master->magic_map, base: 1);
144 master->dev = dev;
145
146 /* initialize the tree of output resource lessees */
147 INIT_LIST_HEAD(list: &master->lessees);
148 INIT_LIST_HEAD(list: &master->lessee_list);
149 idr_init(idr: &master->leases);
150 idr_init_base(idr: &master->lessee_idr, base: 1);
151
152 return master;
153}
154
155static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv,
156 bool new_master)
157{
158 dev->master = drm_master_get(master: 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
165static 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(lock: &fpriv->master_lookup_lock);
178 fpriv->master = new_master;
179 spin_unlock(lock: &fpriv->master_lookup_lock);
180
181 fpriv->is_master = 1;
182 fpriv->authenticated = 1;
183
184 drm_set_master(dev, fpriv, new_master: true);
185
186 if (old_master)
187 drm_master_put(master: &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 */
235static int
236drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv)
237{
238 if (file_priv->was_master &&
239 rcu_access_pointer(file_priv->pid) == task_pid(current))
240 return 0;
241
242 if (!capable(CAP_SYS_ADMIN))
243 return -EACCES;
244
245 return 0;
246}
247
248int drm_setmaster_ioctl(struct drm_device *dev, void *data,
249 struct drm_file *file_priv)
250{
251 int ret;
252
253 mutex_lock(&dev->master_mutex);
254
255 ret = drm_master_check_perm(dev, file_priv);
256 if (ret)
257 goto out_unlock;
258
259 if (drm_is_current_master_locked(fpriv: file_priv))
260 goto out_unlock;
261
262 if (dev->master) {
263 ret = -EBUSY;
264 goto out_unlock;
265 }
266
267 if (!file_priv->master) {
268 ret = -EINVAL;
269 goto out_unlock;
270 }
271
272 if (!file_priv->is_master) {
273 ret = drm_new_set_master(dev, fpriv: file_priv);
274 goto out_unlock;
275 }
276
277 if (file_priv->master->lessor != NULL) {
278 drm_dbg_lease(dev,
279 "Attempt to set lessee %d as master\n",
280 file_priv->master->lessee_id);
281 ret = -EINVAL;
282 goto out_unlock;
283 }
284
285 drm_set_master(dev, fpriv: file_priv, new_master: false);
286out_unlock:
287 mutex_unlock(lock: &dev->master_mutex);
288 return ret;
289}
290
291static void drm_drop_master(struct drm_device *dev,
292 struct drm_file *fpriv)
293{
294 if (dev->driver->master_drop)
295 dev->driver->master_drop(dev, fpriv);
296 drm_master_put(master: &dev->master);
297}
298
299int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
300 struct drm_file *file_priv)
301{
302 int ret;
303
304 mutex_lock(&dev->master_mutex);
305
306 ret = drm_master_check_perm(dev, file_priv);
307 if (ret)
308 goto out_unlock;
309
310 if (!drm_is_current_master_locked(fpriv: file_priv)) {
311 ret = -EINVAL;
312 goto out_unlock;
313 }
314
315 if (!dev->master) {
316 ret = -EINVAL;
317 goto out_unlock;
318 }
319
320 if (file_priv->master->lessor != NULL) {
321 drm_dbg_lease(dev,
322 "Attempt to drop lessee %d as master\n",
323 file_priv->master->lessee_id);
324 ret = -EINVAL;
325 goto out_unlock;
326 }
327
328 drm_drop_master(dev, fpriv: file_priv);
329out_unlock:
330 mutex_unlock(lock: &dev->master_mutex);
331 return ret;
332}
333
334int drm_master_open(struct drm_file *file_priv)
335{
336 struct drm_device *dev = file_priv->minor->dev;
337 int ret = 0;
338
339 /* if there is no current master make this fd it, but do not create
340 * any master object for render clients
341 */
342 mutex_lock(&dev->master_mutex);
343 if (!dev->master) {
344 ret = drm_new_set_master(dev, fpriv: file_priv);
345 } else {
346 spin_lock(lock: &file_priv->master_lookup_lock);
347 file_priv->master = drm_master_get(master: dev->master);
348 spin_unlock(lock: &file_priv->master_lookup_lock);
349 }
350 mutex_unlock(lock: &dev->master_mutex);
351
352 return ret;
353}
354
355void drm_master_release(struct drm_file *file_priv)
356{
357 struct drm_device *dev = file_priv->minor->dev;
358 struct drm_master *master;
359
360 mutex_lock(&dev->master_mutex);
361 master = file_priv->master;
362 if (file_priv->magic)
363 idr_remove(&file_priv->master->magic_map, id: file_priv->magic);
364
365 if (!drm_is_current_master_locked(fpriv: file_priv))
366 goto out;
367
368 drm_legacy_lock_master_cleanup(dev, master);
369
370 if (dev->master == file_priv->master)
371 drm_drop_master(dev, fpriv: file_priv);
372out:
373 if (drm_core_check_feature(dev, feature: DRIVER_MODESET) && file_priv->is_master) {
374 /* Revoke any leases held by this or lessees, but only if
375 * this is the "real" master
376 */
377 drm_lease_revoke(master);
378 }
379
380 /* drop the master reference held by the file priv */
381 if (file_priv->master)
382 drm_master_put(master: &file_priv->master);
383 mutex_unlock(lock: &dev->master_mutex);
384}
385
386/**
387 * drm_master_get - reference a master pointer
388 * @master: &struct drm_master
389 *
390 * Increments the reference count of @master and returns a pointer to @master.
391 */
392struct drm_master *drm_master_get(struct drm_master *master)
393{
394 kref_get(kref: &master->refcount);
395 return master;
396}
397EXPORT_SYMBOL(drm_master_get);
398
399/**
400 * drm_file_get_master - reference &drm_file.master of @file_priv
401 * @file_priv: DRM file private
402 *
403 * Increments the reference count of @file_priv's &drm_file.master and returns
404 * the &drm_file.master. If @file_priv has no &drm_file.master, returns NULL.
405 *
406 * Master pointers returned from this function should be unreferenced using
407 * drm_master_put().
408 */
409struct drm_master *drm_file_get_master(struct drm_file *file_priv)
410{
411 struct drm_master *master = NULL;
412
413 spin_lock(lock: &file_priv->master_lookup_lock);
414 if (!file_priv->master)
415 goto unlock;
416 master = drm_master_get(file_priv->master);
417
418unlock:
419 spin_unlock(lock: &file_priv->master_lookup_lock);
420 return master;
421}
422EXPORT_SYMBOL(drm_file_get_master);
423
424static void drm_master_destroy(struct kref *kref)
425{
426 struct drm_master *master = container_of(kref, struct drm_master, refcount);
427 struct drm_device *dev = master->dev;
428
429 if (drm_core_check_feature(dev, feature: DRIVER_MODESET))
430 drm_lease_destroy(lessee: master);
431
432 drm_legacy_master_rmmaps(dev, master);
433
434 idr_destroy(&master->magic_map);
435 idr_destroy(&master->leases);
436 idr_destroy(&master->lessee_idr);
437
438 kfree(objp: master->unique);
439 kfree(objp: master);
440}
441
442/**
443 * drm_master_put - unreference and clear a master pointer
444 * @master: pointer to a pointer of &struct drm_master
445 *
446 * This decrements the &drm_master behind @master and sets it to NULL.
447 */
448void drm_master_put(struct drm_master **master)
449{
450 kref_put(kref: &(*master)->refcount, release: drm_master_destroy);
451 *master = NULL;
452}
453EXPORT_SYMBOL(drm_master_put);
454
455/* Used by drm_client and drm_fb_helper */
456bool drm_master_internal_acquire(struct drm_device *dev)
457{
458 mutex_lock(&dev->master_mutex);
459 if (dev->master) {
460 mutex_unlock(lock: &dev->master_mutex);
461 return false;
462 }
463
464 return true;
465}
466EXPORT_SYMBOL(drm_master_internal_acquire);
467
468/* Used by drm_client and drm_fb_helper */
469void drm_master_internal_release(struct drm_device *dev)
470{
471 mutex_unlock(lock: &dev->master_mutex);
472}
473EXPORT_SYMBOL(drm_master_internal_release);
474

source code of linux/drivers/gpu/drm/drm_auth.c