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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@ffwll.ch>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210712043508.11584-4-desmondcheongzx@gmail.com
This commit is contained in:
Desmond Cheong Zhi Xi 2021-07-12 12:35:06 +08:00 committed by Daniel Vetter
parent 5eff9585de
commit 1f7ef07cfa
1 changed files with 32 additions and 19 deletions
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51
drivers/gpu/drm/drm_auth.c
View File

@ -61,6 +61,35 @@
* trusted clients. * 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) int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
{ {
struct drm_auth *auth = data; struct drm_auth *auth = data;
@ -223,7 +252,7 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
if (ret) if (ret)
goto out_unlock; goto out_unlock;
if (drm_is_current_master(file_priv)) if (drm_is_current_master_locked(file_priv))
goto out_unlock; goto out_unlock;
if (dev->master) { if (dev->master) {
@ -272,7 +301,7 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
if (ret) if (ret)
goto out_unlock; goto out_unlock;
if (!drm_is_current_master(file_priv)) { if (!drm_is_current_master_locked(file_priv)) {
ret = -EINVAL; ret = -EINVAL;
goto out_unlock; goto out_unlock;
} }
@ -321,7 +350,7 @@ void drm_master_release(struct drm_file *file_priv)
if (file_priv->magic) if (file_priv->magic)
idr_remove(&file_priv->master->magic_map, 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; goto out;
drm_legacy_lock_master_cleanup(dev, master); drm_legacy_lock_master_cleanup(dev, master);
@ -342,22 +371,6 @@ out:
mutex_unlock(&dev->master_mutex); 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 * drm_master_get - reference a master pointer
* @master: &struct drm_master * @master: &struct drm_master