[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20210629033706.20537-3-desmondcheongzx@gmail.com>
Date: Tue, 29 Jun 2021 11:37:05 +0800
From: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
To: maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
tzimmermann@...e.de, airlied@...ux.ie, daniel@...ll.ch,
sumit.semwal@...aro.org, christian.koenig@....com
Cc: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>,
dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
linaro-mm-sig@...ts.linaro.org, skhan@...uxfoundation.org,
gregkh@...uxfoundation.org,
linux-kernel-mentees@...ts.linuxfoundation.org,
emil.l.velikov@...il.com, Daniel Vetter <daniel.vetter@...ll.ch>
Subject: [PATCH v5 2/3] drm: add a locked version of drm_is_current_master
While checking the master status of the DRM file in
drm_is_current_master(), the device's master mutex should be
held. Without the mutex, the pointer fpriv->master may be freed
concurrently by another process calling drm_setmaster_ioctl(). This
could lead to use-after-free errors when the pointer is subsequently
dereferenced in drm_lease_owner().
The callers of drm_is_current_master() from drm_auth.c hold the
device's master mutex, but external callers do not. Hence, we implement
drm_is_current_master_locked() to be used within drm_auth.c, and
modify drm_is_current_master() to grab the device's master mutex
before checking the master status.
Reported-by: Daniel Vetter <daniel.vetter@...ll.ch>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
---
drivers/gpu/drm/drm_auth.c | 51 ++++++++++++++++++++++++--------------
1 file changed, 32 insertions(+), 19 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index f00e5abdbbf4..ab1863c5a5a0 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -61,6 +61,35 @@
* trusted clients.
*/
+static bool drm_is_current_master_locked(struct drm_file *fpriv)
+{
+ lockdep_assert_held_once(&fpriv->minor->dev->master_mutex);
+
+ return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
+}
+
+/**
+ * drm_is_current_master - checks whether @priv is the current master
+ * @fpriv: DRM file private
+ *
+ * Checks whether @fpriv is current master on its device. This decides whether a
+ * client is allowed to run DRM_MASTER IOCTLs.
+ *
+ * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting
+ * - the current master is assumed to own the non-shareable display hardware.
+ */
+bool drm_is_current_master(struct drm_file *fpriv)
+{
+ bool ret;
+
+ mutex_lock(&fpriv->minor->dev->master_mutex);
+ ret = drm_is_current_master_locked(fpriv);
+ mutex_unlock(&fpriv->minor->dev->master_mutex);
+
+ return ret;
+}
+EXPORT_SYMBOL(drm_is_current_master);
+
int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
{
struct drm_auth *auth = data;
@@ -223,7 +252,7 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
if (ret)
goto out_unlock;
- if (drm_is_current_master(file_priv))
+ if (drm_is_current_master_locked(file_priv))
goto out_unlock;
if (dev->master) {
@@ -272,7 +301,7 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
if (ret)
goto out_unlock;
- if (!drm_is_current_master(file_priv)) {
+ if (!drm_is_current_master_locked(file_priv)) {
ret = -EINVAL;
goto out_unlock;
}
@@ -321,7 +350,7 @@ void drm_master_release(struct drm_file *file_priv)
if (file_priv->magic)
idr_remove(&file_priv->master->magic_map, file_priv->magic);
- if (!drm_is_current_master(file_priv))
+ if (!drm_is_current_master_locked(file_priv))
goto out;
drm_legacy_lock_master_cleanup(dev, master);
@@ -342,22 +371,6 @@ void drm_master_release(struct drm_file *file_priv)
mutex_unlock(&dev->master_mutex);
}
-/**
- * drm_is_current_master - checks whether @priv is the current master
- * @fpriv: DRM file private
- *
- * Checks whether @fpriv is current master on its device. This decides whether a
- * client is allowed to run DRM_MASTER IOCTLs.
- *
- * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting
- * - the current master is assumed to own the non-shareable display hardware.
- */
-bool drm_is_current_master(struct drm_file *fpriv)
-{
- return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
-}
-EXPORT_SYMBOL(drm_is_current_master);
-
/**
* drm_master_get - reference a master pointer
* @master: &struct drm_master
--
2.25.1
Powered by blists - more mailing lists