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 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 */ 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 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 } 113 114 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 } 132 133 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 } 154 155 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 } 164 165 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 236 drm_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_tgid(current)) 240 return 0; 241 242 if (!capable(CAP_SYS_ADMIN)) 243 return -EACCES; 244 245 return 0; 246 } 247 248 int 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(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, 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, file_priv, false); 286 out_unlock: 287 mutex_unlock(&dev->master_mutex); 288 return ret; 289 } 290 291 static 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(&dev->master); 297 } 298 299 int 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(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, file_priv); 329 out_unlock: 330 mutex_unlock(&dev->master_mutex); 331 return ret; 332 } 333 334 int 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, file_priv); 345 } else { 346 spin_lock(&file_priv->master_lookup_lock); 347 file_priv->master = drm_master_get(dev->master); 348 spin_unlock(&file_priv->master_lookup_lock); 349 } 350 mutex_unlock(&dev->master_mutex); 351 352 return ret; 353 } 354 355 void 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, file_priv->magic); 364 365 if (!drm_is_current_master_locked(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, file_priv); 372 out: 373 if (drm_core_check_feature(dev, 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(&file_priv->master); 383 mutex_unlock(&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 */ 392 struct drm_master *drm_master_get(struct drm_master *master) 393 { 394 kref_get(&master->refcount); 395 return master; 396 } 397 EXPORT_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 */ 409 struct drm_master *drm_file_get_master(struct drm_file *file_priv) 410 { 411 struct drm_master *master = NULL; 412 413 spin_lock(&file_priv->master_lookup_lock); 414 if (!file_priv->master) 415 goto unlock; 416 master = drm_master_get(file_priv->master); 417 418 unlock: 419 spin_unlock(&file_priv->master_lookup_lock); 420 return master; 421 } 422 EXPORT_SYMBOL(drm_file_get_master); 423 424 static 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, DRIVER_MODESET)) 430 drm_lease_destroy(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(master->unique); 439 kfree(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 */ 448 void drm_master_put(struct drm_master **master) 449 { 450 kref_put(&(*master)->refcount, drm_master_destroy); 451 *master = NULL; 452 } 453 EXPORT_SYMBOL(drm_master_put); 454 455 /* Used by drm_client and drm_fb_helper */ 456 bool drm_master_internal_acquire(struct drm_device *dev) 457 { 458 mutex_lock(&dev->master_mutex); 459 if (dev->master) { 460 mutex_unlock(&dev->master_mutex); 461 return false; 462 } 463 464 return true; 465 } 466 EXPORT_SYMBOL(drm_master_internal_acquire); 467 468 /* Used by drm_client and drm_fb_helper */ 469 void drm_master_internal_release(struct drm_device *dev) 470 { 471 mutex_unlock(&dev->master_mutex); 472 } 473 EXPORT_SYMBOL(drm_master_internal_release); 474