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 guard(mutex)(&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; 106 107 drm_dbg_core(dev, "%u\n", auth->magic); 108 109 return ret < 0 ? ret : 0; 110 } 111 112 int drm_authmagic(struct drm_device *dev, void *data, 113 struct drm_file *file_priv) 114 { 115 struct drm_auth *auth = data; 116 struct drm_file *file; 117 118 drm_dbg_core(dev, "%u\n", auth->magic); 119 120 guard(mutex)(&dev->master_mutex); 121 file = idr_find(&file_priv->master->magic_map, auth->magic); 122 if (file) { 123 file->authenticated = 1; 124 idr_replace(&file_priv->master->magic_map, NULL, auth->magic); 125 } 126 127 return file ? 0 : -EINVAL; 128 } 129 130 struct drm_master *drm_master_create(struct drm_device *dev) 131 { 132 struct drm_master *master; 133 134 master = kzalloc(sizeof(*master), GFP_KERNEL); 135 if (!master) 136 return NULL; 137 138 kref_init(&master->refcount); 139 idr_init_base(&master->magic_map, 1); 140 master->dev = dev; 141 142 /* initialize the tree of output resource lessees */ 143 INIT_LIST_HEAD(&master->lessees); 144 INIT_LIST_HEAD(&master->lessee_list); 145 idr_init(&master->leases); 146 idr_init_base(&master->lessee_idr, 1); 147 148 return master; 149 } 150 151 static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv, 152 bool new_master) 153 { 154 dev->master = drm_master_get(fpriv->master); 155 if (dev->driver->master_set) 156 dev->driver->master_set(dev, fpriv, new_master); 157 158 fpriv->was_master = true; 159 } 160 161 static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) 162 { 163 struct drm_master *old_master; 164 struct drm_master *new_master; 165 166 lockdep_assert_held_once(&dev->master_mutex); 167 168 WARN_ON(fpriv->is_master); 169 old_master = fpriv->master; 170 new_master = drm_master_create(dev); 171 if (!new_master) 172 return -ENOMEM; 173 spin_lock(&fpriv->master_lookup_lock); 174 fpriv->master = new_master; 175 spin_unlock(&fpriv->master_lookup_lock); 176 177 fpriv->is_master = 1; 178 fpriv->authenticated = 1; 179 180 drm_set_master(dev, fpriv, true); 181 182 if (old_master) 183 drm_master_put(&old_master); 184 185 return 0; 186 } 187 188 /* 189 * In the olden days the SET/DROP_MASTER ioctls used to return EACCES when 190 * CAP_SYS_ADMIN was not set. This was used to prevent rogue applications 191 * from becoming master and/or failing to release it. 192 * 193 * At the same time, the first client (for a given VT) is _always_ master. 194 * Thus in order for the ioctls to succeed, one had to _explicitly_ run the 195 * application as root or flip the setuid bit. 196 * 197 * If the CAP_SYS_ADMIN was missing, no other client could become master... 198 * EVER :-( Leading to a) the graphics session dying badly or b) a completely 199 * locked session. 200 * 201 * 202 * As some point systemd-logind was introduced to orchestrate and delegate 203 * master as applicable. It does so by opening the fd and passing it to users 204 * while in itself logind a) does the set/drop master per users' request and 205 * b) * implicitly drops master on VT switch. 206 * 207 * Even though logind looks like the future, there are a few issues: 208 * - some platforms don't have equivalent (Android, CrOS, some BSDs) so 209 * root is required _solely_ for SET/DROP MASTER. 210 * - applications may not be updated to use it, 211 * - any client which fails to drop master* can DoS the application using 212 * logind, to a varying degree. 213 * 214 * * Either due missing CAP_SYS_ADMIN or simply not calling DROP_MASTER. 215 * 216 * 217 * Here we implement the next best thing: 218 * - ensure the logind style of fd passing works unchanged, and 219 * - allow a client to drop/set master, iff it is/was master at a given point 220 * in time. 221 * 222 * Note: DROP_MASTER cannot be free for all, as an arbitrator user could: 223 * - DoS/crash the arbitrator - details would be implementation specific 224 * - open the node, become master implicitly and cause issues 225 * 226 * As a result this fixes the following when using root-less build w/o logind 227 * - startx 228 * - weston 229 * - various compositors based on wlroots 230 */ 231 static int 232 drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv) 233 { 234 if (file_priv->was_master && 235 rcu_access_pointer(file_priv->pid) == task_tgid(current)) 236 return 0; 237 238 if (!capable(CAP_SYS_ADMIN)) 239 return -EACCES; 240 241 return 0; 242 } 243 244 int drm_setmaster_ioctl(struct drm_device *dev, void *data, 245 struct drm_file *file_priv) 246 { 247 int ret; 248 249 guard(mutex)(&dev->master_mutex); 250 251 ret = drm_master_check_perm(dev, file_priv); 252 if (ret) 253 return ret; 254 255 if (drm_is_current_master_locked(file_priv)) 256 return ret; 257 258 if (dev->master) 259 return -EBUSY; 260 261 if (!file_priv->master) 262 return -EINVAL; 263 264 if (!file_priv->is_master) 265 return drm_new_set_master(dev, file_priv); 266 267 if (file_priv->master->lessor != NULL) { 268 drm_dbg_lease(dev, 269 "Attempt to set lessee %d as master\n", 270 file_priv->master->lessee_id); 271 return -EINVAL; 272 } 273 274 drm_set_master(dev, file_priv, false); 275 276 return ret; 277 } 278 279 static void drm_drop_master(struct drm_device *dev, 280 struct drm_file *fpriv) 281 { 282 if (dev->driver->master_drop) 283 dev->driver->master_drop(dev, fpriv); 284 drm_master_put(&dev->master); 285 } 286 287 int drm_dropmaster_ioctl(struct drm_device *dev, void *data, 288 struct drm_file *file_priv) 289 { 290 int ret; 291 292 guard(mutex)(&dev->master_mutex); 293 294 ret = drm_master_check_perm(dev, file_priv); 295 if (ret) 296 return ret; 297 298 if (!drm_is_current_master_locked(file_priv)) 299 return -EINVAL; 300 301 if (!dev->master) 302 return -EINVAL; 303 304 if (file_priv->master->lessor != NULL) { 305 drm_dbg_lease(dev, 306 "Attempt to drop lessee %d as master\n", 307 file_priv->master->lessee_id); 308 return -EINVAL; 309 } 310 311 drm_drop_master(dev, file_priv); 312 313 return ret; 314 } 315 316 int drm_master_open(struct drm_file *file_priv) 317 { 318 struct drm_device *dev = file_priv->minor->dev; 319 int ret = 0; 320 321 /* if there is no current master make this fd it, but do not create 322 * any master object for render clients 323 */ 324 guard(mutex)(&dev->master_mutex); 325 if (!dev->master) { 326 ret = drm_new_set_master(dev, file_priv); 327 } else { 328 spin_lock(&file_priv->master_lookup_lock); 329 file_priv->master = drm_master_get(dev->master); 330 spin_unlock(&file_priv->master_lookup_lock); 331 } 332 333 return ret; 334 } 335 336 void drm_master_release(struct drm_file *file_priv) 337 { 338 struct drm_device *dev = file_priv->minor->dev; 339 struct drm_master *master; 340 341 guard(mutex)(&dev->master_mutex); 342 master = file_priv->master; 343 if (file_priv->magic) 344 idr_remove(&file_priv->master->magic_map, file_priv->magic); 345 346 if (!drm_is_current_master_locked(file_priv)) 347 goto out; 348 349 if (dev->master == file_priv->master) 350 drm_drop_master(dev, file_priv); 351 out: 352 if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) { 353 /* Revoke any leases held by this or lessees, but only if 354 * this is the "real" master 355 */ 356 drm_lease_revoke(master); 357 } 358 359 /* drop the master reference held by the file priv */ 360 if (file_priv->master) 361 drm_master_put(&file_priv->master); 362 } 363 364 /** 365 * drm_master_get - reference a master pointer 366 * @master: &struct drm_master 367 * 368 * Increments the reference count of @master and returns a pointer to @master. 369 */ 370 struct drm_master *drm_master_get(struct drm_master *master) 371 { 372 kref_get(&master->refcount); 373 return master; 374 } 375 EXPORT_SYMBOL(drm_master_get); 376 377 /** 378 * drm_file_get_master - reference &drm_file.master of @file_priv 379 * @file_priv: DRM file private 380 * 381 * Increments the reference count of @file_priv's &drm_file.master and returns 382 * the &drm_file.master. If @file_priv has no &drm_file.master, returns NULL. 383 * 384 * Master pointers returned from this function should be unreferenced using 385 * drm_master_put(). 386 */ 387 struct drm_master *drm_file_get_master(struct drm_file *file_priv) 388 { 389 struct drm_master *master = NULL; 390 391 spin_lock(&file_priv->master_lookup_lock); 392 if (!file_priv->master) 393 goto unlock; 394 master = drm_master_get(file_priv->master); 395 396 unlock: 397 spin_unlock(&file_priv->master_lookup_lock); 398 return master; 399 } 400 EXPORT_SYMBOL(drm_file_get_master); 401 402 static void drm_master_destroy(struct kref *kref) 403 { 404 struct drm_master *master = container_of(kref, struct drm_master, refcount); 405 struct drm_device *dev = master->dev; 406 407 if (drm_core_check_feature(dev, DRIVER_MODESET)) 408 drm_lease_destroy(master); 409 410 idr_destroy(&master->magic_map); 411 idr_destroy(&master->leases); 412 idr_destroy(&master->lessee_idr); 413 414 kfree(master->unique); 415 kfree(master); 416 } 417 418 /** 419 * drm_master_put - unreference and clear a master pointer 420 * @master: pointer to a pointer of &struct drm_master 421 * 422 * This decrements the &drm_master behind @master and sets it to NULL. 423 */ 424 void drm_master_put(struct drm_master **master) 425 { 426 kref_put(&(*master)->refcount, drm_master_destroy); 427 *master = NULL; 428 } 429 EXPORT_SYMBOL(drm_master_put); 430 431 /* Used by drm_client and drm_fb_helper */ 432 bool drm_master_internal_acquire(struct drm_device *dev) 433 { 434 mutex_lock(&dev->master_mutex); 435 if (dev->master) { 436 mutex_unlock(&dev->master_mutex); 437 return false; 438 } 439 440 return true; 441 } 442 EXPORT_SYMBOL(drm_master_internal_acquire); 443 444 /* Used by drm_client and drm_fb_helper */ 445 void drm_master_internal_release(struct drm_device *dev) 446 { 447 mutex_unlock(&dev->master_mutex); 448 } 449 EXPORT_SYMBOL(drm_master_internal_release); 450