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 41 /** 42 * DOC: master and authentication 43 * 44 * &struct drm_master is used to track groups of clients with open 45 * primary device nodes. For every &struct drm_file which has had at 46 * least once successfully became the device master (either through the 47 * SET_MASTER IOCTL, or implicitly through opening the primary device node when 48 * no one else is the current master that time) there exists one &drm_master. 49 * This is noted in &drm_file.is_master. All other clients have just a pointer 50 * to the &drm_master they are associated with. 51 * 52 * In addition only one &drm_master can be the current master for a &drm_device. 53 * It can be switched through the DROP_MASTER and SET_MASTER IOCTL, or 54 * implicitly through closing/opening the primary device node. See also 55 * drm_is_current_master(). 56 * 57 * Clients can authenticate against the current master (if it matches their own) 58 * using the GETMAGIC and AUTHMAGIC IOCTLs. Together with exchanging masters, 59 * this allows controlled access to the device for an entire group of mutually 60 * trusted clients. 61 */ 62 63 static bool drm_is_current_master_locked(struct drm_file *fpriv) 64 { 65 lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) || 66 lockdep_is_held(&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 spin_lock(&fpriv->master_lookup_lock); 86 ret = drm_is_current_master_locked(fpriv); 87 spin_unlock(&fpriv->master_lookup_lock); 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_dbg_core(dev, "%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_dbg_core(dev, "%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 idr_init_base(&master->magic_map, 1); 142 master->dev = dev; 143 144 /* initialize the tree of output resource lessees */ 145 INIT_LIST_HEAD(&master->lessees); 146 INIT_LIST_HEAD(&master->lessee_list); 147 idr_init(&master->leases); 148 idr_init_base(&master->lessee_idr, 1); 149 150 return master; 151 } 152 153 static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv, 154 bool new_master) 155 { 156 dev->master = drm_master_get(fpriv->master); 157 if (dev->driver->master_set) 158 dev->driver->master_set(dev, fpriv, new_master); 159 160 fpriv->was_master = true; 161 } 162 163 static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) 164 { 165 struct drm_master *old_master; 166 struct drm_master *new_master; 167 168 lockdep_assert_held_once(&dev->master_mutex); 169 170 WARN_ON(fpriv->is_master); 171 old_master = fpriv->master; 172 new_master = drm_master_create(dev); 173 if (!new_master) 174 return -ENOMEM; 175 spin_lock(&fpriv->master_lookup_lock); 176 fpriv->master = new_master; 177 spin_unlock(&fpriv->master_lookup_lock); 178 179 fpriv->is_master = 1; 180 fpriv->authenticated = 1; 181 182 drm_set_master(dev, fpriv, true); 183 184 if (old_master) 185 drm_master_put(&old_master); 186 187 return 0; 188 } 189 190 /* 191 * In the olden days the SET/DROP_MASTER ioctls used to return EACCES when 192 * CAP_SYS_ADMIN was not set. This was used to prevent rogue applications 193 * from becoming master and/or failing to release it. 194 * 195 * At the same time, the first client (for a given VT) is _always_ master. 196 * Thus in order for the ioctls to succeed, one had to _explicitly_ run the 197 * application as root or flip the setuid bit. 198 * 199 * If the CAP_SYS_ADMIN was missing, no other client could become master... 200 * EVER :-( Leading to a) the graphics session dying badly or b) a completely 201 * locked session. 202 * 203 * 204 * As some point systemd-logind was introduced to orchestrate and delegate 205 * master as applicable. It does so by opening the fd and passing it to users 206 * while in itself logind a) does the set/drop master per users' request and 207 * b) * implicitly drops master on VT switch. 208 * 209 * Even though logind looks like the future, there are a few issues: 210 * - some platforms don't have equivalent (Android, CrOS, some BSDs) so 211 * root is required _solely_ for SET/DROP MASTER. 212 * - applications may not be updated to use it, 213 * - any client which fails to drop master* can DoS the application using 214 * logind, to a varying degree. 215 * 216 * * Either due missing CAP_SYS_ADMIN or simply not calling DROP_MASTER. 217 * 218 * 219 * Here we implement the next best thing: 220 * - ensure the logind style of fd passing works unchanged, and 221 * - allow a client to drop/set master, iff it is/was master at a given point 222 * in time. 223 * 224 * Note: DROP_MASTER cannot be free for all, as an arbitrator user could: 225 * - DoS/crash the arbitrator - details would be implementation specific 226 * - open the node, become master implicitly and cause issues 227 * 228 * As a result this fixes the following when using root-less build w/o logind 229 * - startx 230 * - weston 231 * - various compositors based on wlroots 232 */ 233 static int 234 drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv) 235 { 236 if (file_priv->was_master && 237 rcu_access_pointer(file_priv->pid) == task_tgid(current)) 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_dbg_lease(dev, 277 "Attempt to set lessee %d as master\n", 278 file_priv->master->lessee_id); 279 ret = -EINVAL; 280 goto out_unlock; 281 } 282 283 drm_set_master(dev, file_priv, false); 284 out_unlock: 285 mutex_unlock(&dev->master_mutex); 286 return ret; 287 } 288 289 static void drm_drop_master(struct drm_device *dev, 290 struct drm_file *fpriv) 291 { 292 if (dev->driver->master_drop) 293 dev->driver->master_drop(dev, fpriv); 294 drm_master_put(&dev->master); 295 } 296 297 int drm_dropmaster_ioctl(struct drm_device *dev, void *data, 298 struct drm_file *file_priv) 299 { 300 int ret; 301 302 mutex_lock(&dev->master_mutex); 303 304 ret = drm_master_check_perm(dev, file_priv); 305 if (ret) 306 goto out_unlock; 307 308 if (!drm_is_current_master_locked(file_priv)) { 309 ret = -EINVAL; 310 goto out_unlock; 311 } 312 313 if (!dev->master) { 314 ret = -EINVAL; 315 goto out_unlock; 316 } 317 318 if (file_priv->master->lessor != NULL) { 319 drm_dbg_lease(dev, 320 "Attempt to drop lessee %d as master\n", 321 file_priv->master->lessee_id); 322 ret = -EINVAL; 323 goto out_unlock; 324 } 325 326 drm_drop_master(dev, file_priv); 327 out_unlock: 328 mutex_unlock(&dev->master_mutex); 329 return ret; 330 } 331 332 int drm_master_open(struct drm_file *file_priv) 333 { 334 struct drm_device *dev = file_priv->minor->dev; 335 int ret = 0; 336 337 /* if there is no current master make this fd it, but do not create 338 * any master object for render clients 339 */ 340 mutex_lock(&dev->master_mutex); 341 if (!dev->master) { 342 ret = drm_new_set_master(dev, file_priv); 343 } else { 344 spin_lock(&file_priv->master_lookup_lock); 345 file_priv->master = drm_master_get(dev->master); 346 spin_unlock(&file_priv->master_lookup_lock); 347 } 348 mutex_unlock(&dev->master_mutex); 349 350 return ret; 351 } 352 353 void drm_master_release(struct drm_file *file_priv) 354 { 355 struct drm_device *dev = file_priv->minor->dev; 356 struct drm_master *master; 357 358 mutex_lock(&dev->master_mutex); 359 master = file_priv->master; 360 if (file_priv->magic) 361 idr_remove(&file_priv->master->magic_map, file_priv->magic); 362 363 if (!drm_is_current_master_locked(file_priv)) 364 goto out; 365 366 if (dev->master == file_priv->master) 367 drm_drop_master(dev, file_priv); 368 out: 369 if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) { 370 /* Revoke any leases held by this or lessees, but only if 371 * this is the "real" master 372 */ 373 drm_lease_revoke(master); 374 } 375 376 /* drop the master reference held by the file priv */ 377 if (file_priv->master) 378 drm_master_put(&file_priv->master); 379 mutex_unlock(&dev->master_mutex); 380 } 381 382 /** 383 * drm_master_get - reference a master pointer 384 * @master: &struct drm_master 385 * 386 * Increments the reference count of @master and returns a pointer to @master. 387 */ 388 struct drm_master *drm_master_get(struct drm_master *master) 389 { 390 kref_get(&master->refcount); 391 return master; 392 } 393 EXPORT_SYMBOL(drm_master_get); 394 395 /** 396 * drm_file_get_master - reference &drm_file.master of @file_priv 397 * @file_priv: DRM file private 398 * 399 * Increments the reference count of @file_priv's &drm_file.master and returns 400 * the &drm_file.master. If @file_priv has no &drm_file.master, returns NULL. 401 * 402 * Master pointers returned from this function should be unreferenced using 403 * drm_master_put(). 404 */ 405 struct drm_master *drm_file_get_master(struct drm_file *file_priv) 406 { 407 struct drm_master *master = NULL; 408 409 spin_lock(&file_priv->master_lookup_lock); 410 if (!file_priv->master) 411 goto unlock; 412 master = drm_master_get(file_priv->master); 413 414 unlock: 415 spin_unlock(&file_priv->master_lookup_lock); 416 return master; 417 } 418 EXPORT_SYMBOL(drm_file_get_master); 419 420 static void drm_master_destroy(struct kref *kref) 421 { 422 struct drm_master *master = container_of(kref, struct drm_master, refcount); 423 struct drm_device *dev = master->dev; 424 425 if (drm_core_check_feature(dev, DRIVER_MODESET)) 426 drm_lease_destroy(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