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 int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) 65 { 66 struct drm_auth *auth = data; 67 int ret = 0; 68 69 mutex_lock(&dev->master_mutex); 70 if (!file_priv->magic) { 71 ret = idr_alloc(&file_priv->master->magic_map, file_priv, 72 1, 0, GFP_KERNEL); 73 if (ret >= 0) 74 file_priv->magic = ret; 75 } 76 auth->magic = file_priv->magic; 77 mutex_unlock(&dev->master_mutex); 78 79 DRM_DEBUG("%u\n", auth->magic); 80 81 return ret < 0 ? ret : 0; 82 } 83 84 int drm_authmagic(struct drm_device *dev, void *data, 85 struct drm_file *file_priv) 86 { 87 struct drm_auth *auth = data; 88 struct drm_file *file; 89 90 DRM_DEBUG("%u\n", auth->magic); 91 92 mutex_lock(&dev->master_mutex); 93 file = idr_find(&file_priv->master->magic_map, auth->magic); 94 if (file) { 95 file->authenticated = 1; 96 idr_replace(&file_priv->master->magic_map, NULL, auth->magic); 97 } 98 mutex_unlock(&dev->master_mutex); 99 100 return file ? 0 : -EINVAL; 101 } 102 103 struct drm_master *drm_master_create(struct drm_device *dev) 104 { 105 struct drm_master *master; 106 107 master = kzalloc(sizeof(*master), GFP_KERNEL); 108 if (!master) 109 return NULL; 110 111 kref_init(&master->refcount); 112 drm_master_legacy_init(master); 113 idr_init(&master->magic_map); 114 master->dev = dev; 115 116 /* initialize the tree of output resource lessees */ 117 INIT_LIST_HEAD(&master->lessees); 118 INIT_LIST_HEAD(&master->lessee_list); 119 idr_init(&master->leases); 120 idr_init(&master->lessee_idr); 121 122 return master; 123 } 124 125 static int drm_set_master(struct drm_device *dev, struct drm_file *fpriv, 126 bool new_master) 127 { 128 int ret = 0; 129 130 dev->master = drm_master_get(fpriv->master); 131 if (dev->driver->master_set) { 132 ret = dev->driver->master_set(dev, fpriv, new_master); 133 if (unlikely(ret != 0)) { 134 drm_master_put(&dev->master); 135 } 136 } 137 138 fpriv->was_master = (ret == 0); 139 return ret; 140 } 141 142 static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) 143 { 144 struct drm_master *old_master; 145 int ret; 146 147 lockdep_assert_held_once(&dev->master_mutex); 148 149 WARN_ON(fpriv->is_master); 150 old_master = fpriv->master; 151 fpriv->master = drm_master_create(dev); 152 if (!fpriv->master) { 153 fpriv->master = old_master; 154 return -ENOMEM; 155 } 156 157 fpriv->is_master = 1; 158 fpriv->authenticated = 1; 159 160 ret = drm_set_master(dev, fpriv, true); 161 if (ret) 162 goto out_err; 163 164 if (old_master) 165 drm_master_put(&old_master); 166 167 return 0; 168 169 out_err: 170 /* drop references and restore old master on failure */ 171 drm_master_put(&fpriv->master); 172 fpriv->master = old_master; 173 fpriv->is_master = 0; 174 175 return ret; 176 } 177 178 /* 179 * In the olden days the SET/DROP_MASTER ioctls used to return EACCES when 180 * CAP_SYS_ADMIN was not set. This was used to prevent rogue applications 181 * from becoming master and/or failing to release it. 182 * 183 * At the same time, the first client (for a given VT) is _always_ master. 184 * Thus in order for the ioctls to succeed, one had to _explicitly_ run the 185 * application as root or flip the setuid bit. 186 * 187 * If the CAP_SYS_ADMIN was missing, no other client could become master... 188 * EVER :-( Leading to a) the graphics session dying badly or b) a completely 189 * locked session. 190 * 191 * 192 * As some point systemd-logind was introduced to orchestrate and delegate 193 * master as applicable. It does so by opening the fd and passing it to users 194 * while in itself logind a) does the set/drop master per users' request and 195 * b) * implicitly drops master on VT switch. 196 * 197 * Even though logind looks like the future, there are a few issues: 198 * - some platforms don't have equivalent (Android, CrOS, some BSDs) so 199 * root is required _solely_ for SET/DROP MASTER. 200 * - applications may not be updated to use it, 201 * - any client which fails to drop master* can DoS the application using 202 * logind, to a varying degree. 203 * 204 * * Either due missing CAP_SYS_ADMIN or simply not calling DROP_MASTER. 205 * 206 * 207 * Here we implement the next best thing: 208 * - ensure the logind style of fd passing works unchanged, and 209 * - allow a client to drop/set master, iff it is/was master at a given point 210 * in time. 211 * 212 * Note: DROP_MASTER cannot be free for all, as an arbitrator user could: 213 * - DoS/crash the arbitrator - details would be implementation specific 214 * - open the node, become master implicitly and cause issues 215 * 216 * As a result this fixes the following when using root-less build w/o logind 217 * - startx 218 * - weston 219 * - various compositors based on wlroots 220 */ 221 static int 222 drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv) 223 { 224 if (file_priv->pid == task_pid(current) && file_priv->was_master) 225 return 0; 226 227 if (!capable(CAP_SYS_ADMIN)) 228 return -EACCES; 229 230 return 0; 231 } 232 233 int drm_setmaster_ioctl(struct drm_device *dev, void *data, 234 struct drm_file *file_priv) 235 { 236 int ret = 0; 237 238 mutex_lock(&dev->master_mutex); 239 240 ret = drm_master_check_perm(dev, file_priv); 241 if (ret) 242 goto out_unlock; 243 244 if (drm_is_current_master(file_priv)) 245 goto out_unlock; 246 247 if (dev->master) { 248 ret = -EBUSY; 249 goto out_unlock; 250 } 251 252 if (!file_priv->master) { 253 ret = -EINVAL; 254 goto out_unlock; 255 } 256 257 if (!file_priv->is_master) { 258 ret = drm_new_set_master(dev, file_priv); 259 goto out_unlock; 260 } 261 262 if (file_priv->master->lessor != NULL) { 263 DRM_DEBUG_LEASE("Attempt to set lessee %d as master\n", file_priv->master->lessee_id); 264 ret = -EINVAL; 265 goto out_unlock; 266 } 267 268 ret = drm_set_master(dev, file_priv, false); 269 out_unlock: 270 mutex_unlock(&dev->master_mutex); 271 return ret; 272 } 273 274 static void drm_drop_master(struct drm_device *dev, 275 struct drm_file *fpriv) 276 { 277 if (dev->driver->master_drop) 278 dev->driver->master_drop(dev, fpriv); 279 drm_master_put(&dev->master); 280 } 281 282 int drm_dropmaster_ioctl(struct drm_device *dev, void *data, 283 struct drm_file *file_priv) 284 { 285 int ret = -EINVAL; 286 287 mutex_lock(&dev->master_mutex); 288 289 ret = drm_master_check_perm(dev, file_priv); 290 if (ret) 291 goto out_unlock; 292 293 ret = -EINVAL; 294 if (!drm_is_current_master(file_priv)) 295 goto out_unlock; 296 297 if (!dev->master) 298 goto out_unlock; 299 300 if (file_priv->master->lessor != NULL) { 301 DRM_DEBUG_LEASE("Attempt to drop lessee %d as master\n", file_priv->master->lessee_id); 302 ret = -EINVAL; 303 goto out_unlock; 304 } 305 306 ret = 0; 307 drm_drop_master(dev, file_priv); 308 out_unlock: 309 mutex_unlock(&dev->master_mutex); 310 return ret; 311 } 312 313 int drm_master_open(struct drm_file *file_priv) 314 { 315 struct drm_device *dev = file_priv->minor->dev; 316 int ret = 0; 317 318 /* if there is no current master make this fd it, but do not create 319 * any master object for render clients */ 320 mutex_lock(&dev->master_mutex); 321 if (!dev->master) 322 ret = drm_new_set_master(dev, file_priv); 323 else 324 file_priv->master = drm_master_get(dev->master); 325 mutex_unlock(&dev->master_mutex); 326 327 return ret; 328 } 329 330 void drm_master_release(struct drm_file *file_priv) 331 { 332 struct drm_device *dev = file_priv->minor->dev; 333 struct drm_master *master = file_priv->master; 334 335 mutex_lock(&dev->master_mutex); 336 if (file_priv->magic) 337 idr_remove(&file_priv->master->magic_map, file_priv->magic); 338 339 if (!drm_is_current_master(file_priv)) 340 goto out; 341 342 drm_legacy_lock_master_cleanup(dev, master); 343 344 if (dev->master == file_priv->master) 345 drm_drop_master(dev, file_priv); 346 out: 347 if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) { 348 /* Revoke any leases held by this or lessees, but only if 349 * this is the "real" master 350 */ 351 drm_lease_revoke(master); 352 } 353 354 /* drop the master reference held by the file priv */ 355 if (file_priv->master) 356 drm_master_put(&file_priv->master); 357 mutex_unlock(&dev->master_mutex); 358 } 359 360 /** 361 * drm_is_current_master - checks whether @priv is the current master 362 * @fpriv: DRM file private 363 * 364 * Checks whether @fpriv is current master on its device. This decides whether a 365 * client is allowed to run DRM_MASTER IOCTLs. 366 * 367 * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting 368 * - the current master is assumed to own the non-shareable display hardware. 369 */ 370 bool drm_is_current_master(struct drm_file *fpriv) 371 { 372 return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; 373 } 374 EXPORT_SYMBOL(drm_is_current_master); 375 376 /** 377 * drm_master_get - reference a master pointer 378 * @master: &struct drm_master 379 * 380 * Increments the reference count of @master and returns a pointer to @master. 381 */ 382 struct drm_master *drm_master_get(struct drm_master *master) 383 { 384 kref_get(&master->refcount); 385 return master; 386 } 387 EXPORT_SYMBOL(drm_master_get); 388 389 static void drm_master_destroy(struct kref *kref) 390 { 391 struct drm_master *master = container_of(kref, struct drm_master, refcount); 392 struct drm_device *dev = master->dev; 393 394 if (drm_core_check_feature(dev, DRIVER_MODESET)) 395 drm_lease_destroy(master); 396 397 drm_legacy_master_rmmaps(dev, master); 398 399 idr_destroy(&master->magic_map); 400 idr_destroy(&master->leases); 401 idr_destroy(&master->lessee_idr); 402 403 kfree(master->unique); 404 kfree(master); 405 } 406 407 /** 408 * drm_master_put - unreference and clear a master pointer 409 * @master: pointer to a pointer of &struct drm_master 410 * 411 * This decrements the &drm_master behind @master and sets it to NULL. 412 */ 413 void drm_master_put(struct drm_master **master) 414 { 415 kref_put(&(*master)->refcount, drm_master_destroy); 416 *master = NULL; 417 } 418 EXPORT_SYMBOL(drm_master_put); 419 420 /* Used by drm_client and drm_fb_helper */ 421 bool drm_master_internal_acquire(struct drm_device *dev) 422 { 423 mutex_lock(&dev->master_mutex); 424 if (dev->master) { 425 mutex_unlock(&dev->master_mutex); 426 return false; 427 } 428 429 return true; 430 } 431 EXPORT_SYMBOL(drm_master_internal_acquire); 432 433 /* Used by drm_client and drm_fb_helper */ 434 void drm_master_internal_release(struct drm_device *dev) 435 { 436 mutex_unlock(&dev->master_mutex); 437 } 438 EXPORT_SYMBOL(drm_master_internal_release); 439