[PATCH] drm: Fix an unwanted master inheritance

[Thomas Hellstrom]

A client calling drmSetMaster() using a file descriptor that was opened
when another client was master would inherit the latter client's master
object and all it's authenticated clients.

This is unwanted behaviour, and when this happens, instead allocate a
brand new master object for the client calling drmSetMaster().

Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
---
 drivers/gpu/drm/drm_drv.c  | 12 +++++++
 drivers/gpu/drm/drm_fops.c | 80 ++++++++++++++++++++++++++++++----------------
 include/drm/drmP.h         |  6 ++++
 3 files changed, 70 insertions(+), 28 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 9362609..1f072ba 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -160,6 +160,18 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
 		goto out_unlock;
 	}
 
+	if (!file_priv->allowed_master) {
+		struct drm_master *saved_master = file_priv->master;
+
+		ret = drm_new_set_master(dev, file_priv);
+		if (ret)
+			file_priv->master = saved_master;
+		else
+			drm_master_put(&saved_master);
+
+		goto out_unlock;
+	}
+
 	file_priv->minor->master = drm_master_get(file_priv->master);
 	file_priv->is_master = 1;
 	if (dev->driver->master_set) {
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index c59ce4d..4b5c11c 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -126,6 +126,56 @@ static int drm_cpu_valid(void)
 }
 
 /**
+ * drm_new_set_master - Allocate a new master object and become master for the
+ * associated master realm.
+ *
+ * @dev: The associated device.
+ * @fpriv: File private identifying the client.
+ *
+ * This function must be called with dev::struct_mutex held. Returns negative
+ * error code on failure, zero on success.
+ */
+int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
+{
+	int ret;
+
+	lockdep_assert_held_once(&dev->master_mutex);
+	/* create a new master */
+	fpriv->minor->master = drm_master_create(fpriv->minor);
+	if (!fpriv->minor->master)
+		return -ENOMEM;
+
+	fpriv->is_master = 1;
+	fpriv->allowed_master = 1;
+
+	/* take another reference for the copy in the local file priv */
+	fpriv->master = drm_master_get(fpriv->minor->master);
+
+	fpriv->authenticated = 1;
+
+	if (dev->driver->master_create) {
+		ret = dev->driver->master_create(dev, fpriv->master);
+		if (ret) {
+			/* drop both references if this fails */
+			drm_master_put(&fpriv->minor->master);
+			drm_master_put(&fpriv->master);
+			return ret;
+		}
+	}
+	if (dev->driver->master_set) {
+		ret = dev->driver->master_set(dev, fpriv, true);
+		if (ret) {
+			/* drop both references if this fails */
+			drm_master_put(&fpriv->minor->master);
+			drm_master_put(&fpriv->master);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+/**
  * Called whenever a process opens /dev/drm.
  *
  * \param filp file pointer.
@@ -189,35 +239,9 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
 	mutex_lock(&dev->master_mutex);
 	if (drm_is_primary_client(priv) && !priv->minor->master) {
 		/* create a new master */
-		priv->minor->master = drm_master_create(priv->minor);
-		if (!priv->minor->master) {
-			ret = -ENOMEM;
+		ret = drm_new_set_master(dev, priv);
+		if (ret)
 			goto out_close;
-		}
-
-		priv->is_master = 1;
-		/* take another reference for the copy in the local file priv */
-		priv->master = drm_master_get(priv->minor->master);
-		priv->authenticated = 1;
-
-		if (dev->driver->master_create) {
-			ret = dev->driver->master_create(dev, priv->master);
-			if (ret) {
-				/* drop both references if this fails */
-				drm_master_put(&priv->minor->master);
-				drm_master_put(&priv->master);
-				goto out_close;
-			}
-		}
-		if (dev->driver->master_set) {
-			ret = dev->driver->master_set(dev, priv, true);
-			if (ret) {
-				/* drop both references if this fails */
-				drm_master_put(&priv->minor->master);
-				drm_master_put(&priv->master);
-				goto out_close;
-			}
-		}
 	} else if (drm_is_primary_client(priv)) {
 		/* get a reference to the master */
 		priv->master = drm_master_get(priv->minor->master);
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 0b921ae..566b59e 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -309,6 +309,11 @@ struct drm_file {
 	unsigned universal_planes:1;
 	/* true if client understands atomic properties */
 	unsigned atomic:1;
+	/*
+	 * This client is allowed to gain master privileges for @master.
+	 * Protected by struct drm_device::master_mutex.
+	 */
+	unsigned allowed_master:1;
 
 	struct pid *pid;
 	kuid_t uid;
@@ -910,6 +915,7 @@ extern int drm_open(struct inode *inode, struct file *filp);
 extern ssize_t drm_read(struct file *filp, char __user *buffer,
 			size_t count, loff_t *offset);
 extern int drm_release(struct inode *inode, struct file *filp);
+extern int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv);
 
 				/* Mapping support (drm_vm.h) */
 extern unsigned int drm_poll(struct file *filp, struct poll_table_struct *wait);
-- 
2.5.0