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