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/openeing 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 64 static bool drm_is_current_master_locked(struct drm_file *fpriv) 65 { 66 lockdep_assert_held_once(&fpriv->minor->dev->master_mutex); 67 68 return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; 69 } 70 71 /** 72 * drm_is_current_master - checks whether @priv is the current master 73 * @fpriv: DRM file private 74 * 75 * Checks whether @fpriv is current master on its device. This decides whether a 76 * client is allowed to run DRM_MASTER IOCTLs. 77 * 78 * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting 79 * - the current master is assumed to own the non-shareable display hardware. 80 */ 81 bool drm_is_current_master(struct drm_file *fpriv) 82 { 83 bool ret; 84 85 mutex_lock(&fpriv->minor->dev->master_mutex); 86 ret = drm_is_current_master_locked(fpriv); 87 mutex_unlock(&fpriv->minor->dev->master_mutex); 88 89 return ret; 90 } 91 EXPORT_SYMBOL(drm_is_current_master); 92 93 int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) 94 { 95 struct drm_auth *auth = data; 96 int ret = 0; 97 98 mutex_lock(&dev->master_mutex); 99 if (!file_priv->magic) { 100 ret = idr_alloc(&file_priv->master->magic_map, file_priv, 101 1, 0, GFP_KERNEL); 102 if (ret >= 0) 103 file_priv->magic = ret; 104 } 105 auth->magic = file_priv->magic; 106 mutex_unlock(&dev->master_mutex); 107 108 DRM_DEBUG("%u\n", auth->magic); 109 110 return ret < 0 ? ret : 0; 111 } 112 113 int 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_DEBUG("%u\n", auth->magic); 120 121 mutex_lock(&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 mutex_unlock(&dev->master_mutex); 128 129 return file ? 0 : -EINVAL; 130 } 131 132 struct drm_master *drm_master_create(struct drm_device *dev) 133 { 134 struct drm_master *master; 135 136 master = kzalloc(sizeof(*master), GFP_KERNEL); 137 if (!master) 138 return NULL; 139 140 kref_init(&master->refcount); 141 drm_master_legacy_init(master); 142 idr_init(&master->magic_map); 143 master->dev = dev; 144 145 /* initialize the tree of output resource lessees */ 146 INIT_LIST_HEAD(&master->lessees); 147 INIT_LIST_HEAD(&master->lessee_list); 148 idr_init(&master->leases); 149 idr_init(&master->lessee_idr); 150 151 return master; 152 } 153 154 static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv, 155 bool new_master) 156 { 157 dev->master = drm_master_get(fpriv->master); 158 if (dev->driver->master_set) 159 dev->driver->master_set(dev, fpriv, new_master); 160 161 fpriv->was_master = true; 162 } 163 164 static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) 165 { 166 struct drm_master *old_master; 167 struct drm_master *new_master; 168 169 lockdep_assert_held_once(&dev->master_mutex); 170 171 WARN_ON(fpriv->is_master); 172 old_master = fpriv->master; 173 new_master = drm_master_create(dev); 174 if (!new_master) 175 return -ENOMEM; 176 spin_lock(&fpriv->master_lookup_lock); 177 fpriv->master = new_master; 178 spin_unlock(&fpriv->master_lookup_lock); 179 180 fpriv->is_master = 1; 181 fpriv->authenticated = 1; 182 183 drm_set_master(dev, fpriv, true); 184 185 if (old_master) 186 drm_master_put(&old_master); 187 188 return 0; 189 } 190 191 /* 192 * In the olden days the SET/DROP_MASTER ioctls used to return EACCES when 193 * CAP_SYS_ADMIN was not set. This was used to prevent rogue applications 194 * from becoming master and/or failing to release it. 195 * 196 * At the same time, the first client (for a given VT) is _always_ master. 197 * Thus in order for the ioctls to succeed, one had to _explicitly_ run the 198 * application as root or flip the setuid bit. 199 * 200 * If the CAP_SYS_ADMIN was missing, no other client could become master... 201 * EVER :-( Leading to a) the graphics session dying badly or b) a completely 202 * locked session. 203 * 204 * 205 * As some point systemd-logind was introduced to orchestrate and delegate 206 * master as applicable. It does so by opening the fd and passing it to users 207 * while in itself logind a) does the set/drop master per users' request and 208 * b) * implicitly drops master on VT switch. 209 * 210 * Even though logind looks like the future, there are a few issues: 211 * - some platforms don't have equivalent (Android, CrOS, some BSDs) so 212 * root is required _solely_ for SET/DROP MASTER. 213 * - applications may not be updated to use it, 214 * - any client which fails to drop master* can DoS the application using 215 * logind, to a varying degree. 216 * 217 * * Either due missing CAP_SYS_ADMIN or simply not calling DROP_MASTER. 218 * 219 * 220 * Here we implement the next best thing: 221 * - ensure the logind style of fd passing works unchanged, and 222 * - allow a client to drop/set master, iff it is/was master at a given point 223 * in time. 224 * 225 * Note: DROP_MASTER cannot be free for all, as an arbitrator user could: 226 * - DoS/crash the arbitrator - details would be implementation specific 227 * - open the node, become master implicitly and cause issues 228 * 229 * As a result this fixes the following when using root-less build w/o logind 230 * - startx 231 * - weston 232 * - various compositors based on wlroots 233 */ 234 static int 235 drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv) 236 { 237 if (file_priv->pid == task_pid(current) && file_priv->was_master) 238 return 0; 239 240 if (!capable(CAP_SYS_ADMIN)) 241 return -EACCES; 242 243 return 0; 244 } 245 246 int drm_setmaster_ioctl(struct drm_device *dev, void *data, 247 struct drm_file *file_priv) 248 { 249 int ret; 250 251 mutex_lock(&dev->master_mutex); 252 253 ret = drm_master_check_perm(dev, file_priv); 254 if (ret) 255 goto out_unlock; 256 257 if (drm_is_current_master_locked(file_priv)) 258 goto out_unlock; 259 260 if (dev->master) { 261 ret = -EBUSY; 262 goto out_unlock; 263 } 264 265 if (!file_priv->master) { 266 ret = -EINVAL; 267 goto out_unlock; 268 } 269 270 if (!file_priv->is_master) { 271 ret = drm_new_set_master(dev, file_priv); 272 goto out_unlock; 273 } 274 275 if (file_priv->master->lessor != NULL) { 276 DRM_DEBUG_LEASE("Attempt to set lessee %d as master\n", file_priv->master->lessee_id); 277 ret = -EINVAL; 278 goto out_unlock; 279 } 280 281 drm_set_master(dev, file_priv, false); 282 out_unlock: 283 mutex_unlock(&dev->master_mutex); 284 return ret; 285 } 286 287 static void drm_drop_master(struct drm_device *dev, 288 struct drm_file *fpriv) 289 { 290 if (dev->driver->master_drop) 291 dev->driver->master_drop(dev, fpriv); 292 drm_master_put(&dev->master); 293 } 294 295 int drm_dropmaster_ioctl(struct drm_device *dev, void *data, 296 struct drm_file *file_priv) 297 { 298 int ret; 299 300 mutex_lock(&dev->master_mutex); 301 302 ret = drm_master_check_perm(dev, file_priv); 303 if (ret) 304 goto out_unlock; 305 306 if (!drm_is_current_master_locked(file_priv)) { 307 ret = -EINVAL; 308 goto out_unlock; 309 } 310 311 if (!dev->master) { 312 ret = -EINVAL; 313 goto out_unlock; 314 } 315 316 if (file_priv->master->lessor != NULL) { 317 DRM_DEBUG_LEASE("Attempt to drop lessee %d as master\n", file_priv->master->lessee_id); 318 ret = -EINVAL; 319 goto out_unlock; 320 } 321 322 drm_drop_master(dev, file_priv); 323 out_unlock: 324 mutex_unlock(&dev->master_mutex); 325 return ret; 326 } 327 328 int drm_master_open(struct drm_file *file_priv) 329 { 330 struct drm_device *dev = file_priv->minor->dev; 331 int ret = 0; 332 333 /* if there is no current master make this fd it, but do not create 334 * any master object for render clients 335 */ 336 mutex_lock(&dev->master_mutex); 337 if (!dev->master) { 338 ret = drm_new_set_master(dev, file_priv); 339 } else { 340 spin_lock(&file_priv->master_lookup_lock); 341 file_priv->master = drm_master_get(dev->master); 342 spin_unlock(&file_priv->master_lookup_lock); 343 } 344 mutex_unlock(&dev->master_mutex); 345 346 return ret; 347 } 348 349 void drm_master_release(struct drm_file *file_priv) 350 { 351 struct drm_device *dev = file_priv->minor->dev; 352 struct drm_master *master; 353 354 mutex_lock(&dev->master_mutex); 355 master = file_priv->master; 356 if (file_priv->magic) 357 idr_remove(&file_priv->master->magic_map, file_priv->magic); 358 359 if (!drm_is_current_master_locked(file_priv)) 360 goto out; 361 362 drm_legacy_lock_master_cleanup(dev, master); 363 364 if (dev->master == file_priv->master) 365 drm_drop_master(dev, file_priv); 366 out: 367 if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) { 368 /* Revoke any leases held by this or lessees, but only if 369 * this is the "real" master 370 */ 371 drm_lease_revoke(master); 372 } 373 374 /* drop the master reference held by the file priv */ 375 if (file_priv->master) 376 drm_master_put(&file_priv->master); 377 mutex_unlock(&dev->master_mutex); 378 } 379 380 /** 381 * drm_master_get - reference a master pointer 382 * @master: &struct drm_master 383 * 384 * Increments the reference count of @master and returns a pointer to @master. 385 */ 386 struct drm_master *drm_master_get(struct drm_master *master) 387 { 388 kref_get(&master->refcount); 389 return master; 390 } 391 EXPORT_SYMBOL(drm_master_get); 392 393 /** 394 * drm_file_get_master - reference &drm_file.master of @file_priv 395 * @file_priv: DRM file private 396 * 397 * Increments the reference count of @file_priv's &drm_file.master and returns 398 * the &drm_file.master. If @file_priv has no &drm_file.master, returns NULL. 399 * 400 * Master pointers returned from this function should be unreferenced using 401 * drm_master_put(). 402 */ 403 struct drm_master *drm_file_get_master(struct drm_file *file_priv) 404 { 405 struct drm_master *master = NULL; 406 407 spin_lock(&file_priv->master_lookup_lock); 408 if (!file_priv->master) 409 goto unlock; 410 master = drm_master_get(file_priv->master); 411 412 unlock: 413 spin_unlock(&file_priv->master_lookup_lock); 414 return master; 415 } 416 EXPORT_SYMBOL(drm_file_get_master); 417 418 static void drm_master_destroy(struct kref *kref) 419 { 420 struct drm_master *master = container_of(kref, struct drm_master, refcount); 421 struct drm_device *dev = master->dev; 422 423 if (drm_core_check_feature(dev, DRIVER_MODESET)) 424 drm_lease_destroy(master); 425 426 drm_legacy_master_rmmaps(dev, master); 427 428 idr_destroy(&master->magic_map); 429 idr_destroy(&master->leases); 430 idr_destroy(&master->lessee_idr); 431 432 kfree(master->unique); 433 kfree(master); 434 } 435 436 /** 437 * drm_master_put - unreference and clear a master pointer 438 * @master: pointer to a pointer of &struct drm_master 439 * 440 * This decrements the &drm_master behind @master and sets it to NULL. 441 */ 442 void drm_master_put(struct drm_master **master) 443 { 444 kref_put(&(*master)->refcount, drm_master_destroy); 445 *master = NULL; 446 } 447 EXPORT_SYMBOL(drm_master_put); 448 449 /* Used by drm_client and drm_fb_helper */ 450 bool drm_master_internal_acquire(struct drm_device *dev) 451 { 452 mutex_lock(&dev->master_mutex); 453 if (dev->master) { 454 mutex_unlock(&dev->master_mutex); 455 return false; 456 } 457 458 return true; 459 } 460 EXPORT_SYMBOL(drm_master_internal_acquire); 461 462 /* Used by drm_client and drm_fb_helper */ 463 void drm_master_internal_release(struct drm_device *dev) 464 { 465 mutex_unlock(&dev->master_mutex); 466 } 467 EXPORT_SYMBOL(drm_master_internal_release); 468