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/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 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 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 } 112 113 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 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 } 130 131 struct drm_master *drm_master_create(struct drm_device *dev) 132 { 133 struct drm_master *master; 134 135 master = kzalloc(sizeof(*master), GFP_KERNEL); 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 } 151 152 static 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 } 161 162 static 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 */ 232 static int 233 drm_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 } 244 245 int 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 } 279 280 static 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 } 287 288 int 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 } 316 317 int 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 } 336 337 void 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 == file_priv->master) 351 drm_drop_master(dev, file_priv); 352 out: 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 */ 371 struct drm_master *drm_master_get(struct drm_master *master) 372 { 373 kref_get(&master->refcount); 374 return master; 375 } 376 EXPORT_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 */ 388 struct 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); 396 397 unlock: 398 spin_unlock(&file_priv->master_lookup_lock); 399 return master; 400 } 401 EXPORT_SYMBOL(drm_file_get_master); 402 403 static 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 */ 425 void drm_master_put(struct drm_master **master) 426 { 427 kref_put(&(*master)->refcount, drm_master_destroy); 428 *master = NULL; 429 } 430 EXPORT_SYMBOL(drm_master_put); 431 432 /* Used by drm_client and drm_fb_helper */ 433 bool 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 } 443 EXPORT_SYMBOL(drm_master_internal_acquire); 444 445 /* Used by drm_client and drm_fb_helper */ 446 void drm_master_internal_release(struct drm_device *dev) 447 { 448 mutex_unlock(&dev->master_mutex); 449 } 450 EXPORT_SYMBOL(drm_master_internal_release); 451