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2024-01-05 071106ecf68c401173c58808b1cf5f68cc50d390 
 kernel/drivers/gpu/drm/drm_auth.c
....@@ -28,10 +28,16 @@
2828  * OTHER DEALINGS IN THE SOFTWARE.
2929  */
3030 
31
-#include <drm/drmP.h>
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
+
3239 #include "drm_internal.h"
3340 #include "drm_legacy.h"
34
-#include <drm/drm_lease.h>
3541 
3642 /**
3743  * DOC: master and authentication
....@@ -103,14 +109,11 @@
103109 		return NULL;
104110 
105111 	kref_init(&master->refcount);
106
-	spin_lock_init(&master->lock.spinlock);
107
-	init_waitqueue_head(&master->lock.lock_queue);
112
+	drm_master_legacy_init(master);
108113 	idr_init(&master->magic_map);
109114 	master->dev = dev;
110115 
111116 	/* initialize the tree of output resource lessees */
112
-	master->lessor = NULL;
113
-	master->lessee_id = 0;
114117 	INIT_LIST_HEAD(&master->lessees);
115118 	INIT_LIST_HEAD(&master->lessee_list);
116119 	idr_init(&master->leases);
....@@ -119,26 +122,19 @@
119122 	return master;
120123 }
121124 
122
-static int drm_set_master(struct drm_device *dev, struct drm_file *fpriv,
123
-			  bool new_master)
125
+static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv,
126
+			   bool new_master)
124127 {
125
-	int ret = 0;
126
-
127128 	dev->master = drm_master_get(fpriv->master);
128
-	if (dev->driver->master_set) {
129
-		ret = dev->driver->master_set(dev, fpriv, new_master);
130
-		if (unlikely(ret != 0)) {
131
-			drm_master_put(&dev->master);
132
-		}
133
-	}
129
+	if (dev->driver->master_set)
130
+		dev->driver->master_set(dev, fpriv, new_master);
134131 
135
-	return ret;
132
+	fpriv->was_master = true;
136133 }
137134 
138135 static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
139136 {
140137 	struct drm_master *old_master;
141
-	int ret;
142138 
143139 	lockdep_assert_held_once(&dev->master_mutex);
144140 
....@@ -150,43 +146,88 @@
150146 		return -ENOMEM;
151147 	}
152148 
153
-	if (dev->driver->master_create) {
154
-		ret = dev->driver->master_create(dev, fpriv->master);
155
-		if (ret)
156
-			goto out_err;
157
-	}
158149 	fpriv->is_master = 1;
159150 	fpriv->authenticated = 1;
160151 
161
-	ret = drm_set_master(dev, fpriv, true);
162
-	if (ret)
163
-		goto out_err;
152
+	drm_set_master(dev, fpriv, true);
164153 
165154 	if (old_master)
166155 		drm_master_put(&old_master);
167156 
168157 	return 0;
158
+}
169159 
170
-out_err:
171
-	/* drop references and restore old master on failure */
172
-	drm_master_put(&fpriv->master);
173
-	fpriv->master = old_master;
174
-	fpriv->is_master = 0;
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;
175208 
176
-	return ret;
209
+	if (!capable(CAP_SYS_ADMIN))
210
+		return -EACCES;
211
+
212
+	return 0;
177213 }
178214 
179215 int drm_setmaster_ioctl(struct drm_device *dev, void *data,
180216 			struct drm_file *file_priv)
181217 {
182
-	int ret = 0;
218
+	int ret;
183219 
184220 	mutex_lock(&dev->master_mutex);
221
+
222
+	ret = drm_master_check_perm(dev, file_priv);
223
+	if (ret)
224
+		goto out_unlock;
225
+
185226 	if (drm_is_current_master(file_priv))
186227 		goto out_unlock;
187228 
188229 	if (dev->master) {
189
-		ret = -EINVAL;
230
+		ret = -EBUSY;
190231 		goto out_unlock;
191232 	}
192233 
....@@ -206,7 +247,7 @@
206247 		goto out_unlock;
207248 	}
208249 
209
-	ret = drm_set_master(dev, file_priv, false);
250
+	drm_set_master(dev, file_priv, false);
210251 out_unlock:
211252 	mutex_unlock(&dev->master_mutex);
212253 	return ret;
....@@ -223,14 +264,23 @@
223264 int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
224265 			 struct drm_file *file_priv)
225266 {
226
-	int ret = -EINVAL;
267
+	int ret;
227268 
228269 	mutex_lock(&dev->master_mutex);
229
-	if (!drm_is_current_master(file_priv))
270
+
271
+	ret = drm_master_check_perm(dev, file_priv);
272
+	if (ret)
230273 		goto out_unlock;
231274 
232
-	if (!dev->master)
275
+	if (!drm_is_current_master(file_priv)) {
276
+		ret = -EINVAL;
233277 		goto out_unlock;
278
+	}
279
+
280
+	if (!dev->master) {
281
+		ret = -EINVAL;
282
+		goto out_unlock;
283
+	}
234284 
235285 	if (file_priv->master->lessor != NULL) {
236286 		DRM_DEBUG_LEASE("Attempt to drop lessee %d as master\n", file_priv->master->lessee_id);
....@@ -238,7 +288,6 @@
238288 		goto out_unlock;
239289 	}
240290 
241
-	ret = 0;
242291 	drm_drop_master(dev, file_priv);
243292 out_unlock:
244293 	mutex_unlock(&dev->master_mutex);
....@@ -275,21 +324,7 @@
275324 	if (!drm_is_current_master(file_priv))
276325 		goto out;
277326 
278
-	if (drm_core_check_feature(dev, DRIVER_LEGACY)) {
279
-		/*
280
-		 * Since the master is disappearing, so is the
281
-		 * possibility to lock.
282
-		 */
283
-		mutex_lock(&dev->struct_mutex);
284
-		if (master->lock.hw_lock) {
285
-			if (dev->sigdata.lock == master->lock.hw_lock)
286
-				dev->sigdata.lock = NULL;
287
-			master->lock.hw_lock = NULL;
288
-			master->lock.file_priv = NULL;
289
-			wake_up_interruptible_all(&master->lock.lock_queue);
290
-		}
291
-		mutex_unlock(&dev->struct_mutex);
292
-	}
327
+	drm_legacy_lock_master_cleanup(dev, master);
293328 
294329 	if (dev->master == file_priv->master)
295330 		drm_drop_master(dev, file_priv);
....@@ -344,9 +379,6 @@
344379 	if (drm_core_check_feature(dev, DRIVER_MODESET))
345380 		drm_lease_destroy(master);
346381 
347
-	if (dev->driver->master_destroy)
348
-		dev->driver->master_destroy(dev, master);
349
-
350382 	drm_legacy_master_rmmaps(dev, master);
351383 
352384 	idr_destroy(&master->magic_map);
....@@ -369,3 +401,23 @@
369401 	*master = NULL;
370402 }
371403 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);