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 if (file_priv->pid == task_pid(current) && file_priv->was_master) 207 return 0; 208 209 if (!capable(CAP_SYS_ADMIN)) 210 return -EACCES; 211 212 return 0; 213 } 214 215 int drm_setmaster_ioctl(struct drm_device *dev, void *data, 216 struct drm_file *file_priv) 217 { 218 int ret; 219 220 mutex_lock(&dev->master_mutex); 221 222 ret = drm_master_check_perm(dev, file_priv); 223 if (ret) 224 goto out_unlock; 225 226 if (drm_is_current_master(file_priv)) 227 goto out_unlock; 228 229 if (dev->master) { 230 ret = -EBUSY; 231 goto out_unlock; 232 } 233 234 if (!file_priv->master) { 235 ret = -EINVAL; 236 goto out_unlock; 237 } 238 239 if (!file_priv->is_master) { 240 ret = drm_new_set_master(dev, file_priv); 241 goto out_unlock; 242 } 243 244 if (file_priv->master->lessor != NULL) { 245 DRM_DEBUG_LEASE("Attempt to set lessee %d as master\n", file_priv->master->lessee_id); 246 ret = -EINVAL; 247 goto out_unlock; 248 } 249 250 drm_set_master(dev, file_priv, false); 251 out_unlock: 252 mutex_unlock(&dev->master_mutex); 253 return ret; 254 } 255 256 static void drm_drop_master(struct drm_device *dev, 257 struct drm_file *fpriv) 258 { 259 if (dev->driver->master_drop) 260 dev->driver->master_drop(dev, fpriv); 261 drm_master_put(&dev->master); 262 } 263 264 int drm_dropmaster_ioctl(struct drm_device *dev, void *data, 265 struct drm_file *file_priv) 266 { 267 int ret; 268 269 mutex_lock(&dev->master_mutex); 270 271 ret = drm_master_check_perm(dev, file_priv); 272 if (ret) 273 goto out_unlock; 274 275 if (!drm_is_current_master(file_priv)) { 276 ret = -EINVAL; 277 goto out_unlock; 278 } 279 280 if (!dev->master) { 281 ret = -EINVAL; 282 goto out_unlock; 283 } 284 285 if (file_priv->master->lessor != NULL) { 286 DRM_DEBUG_LEASE("Attempt to drop lessee %d as master\n", file_priv->master->lessee_id); 287 ret = -EINVAL; 288 goto out_unlock; 289 } 290 291 drm_drop_master(dev, file_priv); 292 out_unlock: 293 mutex_unlock(&dev->master_mutex); 294 return ret; 295 } 296 297 int drm_master_open(struct drm_file *file_priv) 298 { 299 struct drm_device *dev = file_priv->minor->dev; 300 int ret = 0; 301 302 /* if there is no current master make this fd it, but do not create 303 * any master object for render clients */ 304 mutex_lock(&dev->master_mutex); 305 if (!dev->master) 306 ret = drm_new_set_master(dev, file_priv); 307 else 308 file_priv->master = drm_master_get(dev->master); 309 mutex_unlock(&dev->master_mutex); 310 311 return ret; 312 } 313 314 void drm_master_release(struct drm_file *file_priv) 315 { 316 struct drm_device *dev = file_priv->minor->dev; 317 struct drm_master *master; 318 319 mutex_lock(&dev->master_mutex); 320 master = file_priv->master; 321 if (file_priv->magic) 322 idr_remove(&file_priv->master->magic_map, file_priv->magic); 323 324 if (!drm_is_current_master(file_priv)) 325 goto out; 326 327 drm_legacy_lock_master_cleanup(dev, master); 328 329 if (dev->master == file_priv->master) 330 drm_drop_master(dev, file_priv); 331 out: 332 if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) { 333 /* Revoke any leases held by this or lessees, but only if 334 * this is the "real" master 335 */ 336 drm_lease_revoke(master); 337 } 338 339 /* drop the master reference held by the file priv */ 340 if (file_priv->master) 341 drm_master_put(&file_priv->master); 342 mutex_unlock(&dev->master_mutex); 343 } 344 345 /** 346 * drm_is_current_master - checks whether @priv is the current master 347 * @fpriv: DRM file private 348 * 349 * Checks whether @fpriv is current master on its device. This decides whether a 350 * client is allowed to run DRM_MASTER IOCTLs. 351 * 352 * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting 353 * - the current master is assumed to own the non-shareable display hardware. 354 */ 355 bool drm_is_current_master(struct drm_file *fpriv) 356 { 357 return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; 358 } 359 EXPORT_SYMBOL(drm_is_current_master); 360 361 /** 362 * drm_master_get - reference a master pointer 363 * @master: &struct drm_master 364 * 365 * Increments the reference count of @master and returns a pointer to @master. 366 */ 367 struct drm_master *drm_master_get(struct drm_master *master) 368 { 369 kref_get(&master->refcount); 370 return master; 371 } 372 EXPORT_SYMBOL(drm_master_get); 373 374 static void drm_master_destroy(struct kref *kref) 375 { 376 struct drm_master *master = container_of(kref, struct drm_master, refcount); 377 struct drm_device *dev = master->dev; 378 379 if (drm_core_check_feature(dev, DRIVER_MODESET)) 380 drm_lease_destroy(master); 381 382 drm_legacy_master_rmmaps(dev, master); 383 384 idr_destroy(&master->magic_map); 385 idr_destroy(&master->leases); 386 idr_destroy(&master->lessee_idr); 387 388 kfree(master->unique); 389 kfree(master); 390 } 391 392 /** 393 * drm_master_put - unreference and clear a master pointer 394 * @master: pointer to a pointer of &struct drm_master 395 * 396 * This decrements the &drm_master behind @master and sets it to NULL. 397 */ 398 void drm_master_put(struct drm_master **master) 399 { 400 kref_put(&(*master)->refcount, drm_master_destroy); 401 *master = NULL; 402 } 403 EXPORT_SYMBOL(drm_master_put); 404 405 /* Used by drm_client and drm_fb_helper */ 406 bool drm_master_internal_acquire(struct drm_device *dev) 407 { 408 mutex_lock(&dev->master_mutex); 409 if (dev->master) { 410 mutex_unlock(&dev->master_mutex); 411 return false; 412 } 413 414 return true; 415 } 416 EXPORT_SYMBOL(drm_master_internal_acquire); 417 418 /* Used by drm_client and drm_fb_helper */ 419 void drm_master_internal_release(struct drm_device *dev) 420 { 421 mutex_unlock(&dev->master_mutex); 422 } 423 EXPORT_SYMBOL(drm_master_internal_release); 424