On Sat, 12 Jun 2021 at 13:55, Desmond Cheong Zhi Xi desmondcheongzx@gmail.com wrote:
This patch ensures that the device's master mutex is acquired before accessing pointers to struct drm_master that are subsequently dereferenced. Without the mutex, the struct drm_master may be freed concurrently by another process calling drm_setmaster_ioctl(). This could then lead to use-after-free errors.
Reported-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com
<snip>
@@ -578,6 +594,7 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, /* Hook up the fd */ fd_install(fd, lessee_file);
mutex_unlock(&dev->master_mutex);
I was going to suggest pushing the unlock call further up - after the drm_lease_create call. Although that would make the error path rather messy, so let's keep it as-is.
<snip>
@@ -662,7 +684,7 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, struct drm_mode_get_lease *arg = data; __u32 __user *object_ids = (__u32 __user *) (uintptr_t) (arg->objects_ptr); __u32 count_objects = arg->count_objects;
struct drm_master *lessee = lessee_priv->master;
struct drm_master *lessee; struct idr *object_idr; int count; void *entry;@@ -678,8 +700,10 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev,
DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id);
mutex_lock(&dev->master_mutex);
As-is we're dereferencing an uninitialised pointer in DRM_DEBUG_LEASE. Move the lock and assignment before the DRM_DEBUG_LEASE, just like you've done in the list ioctl.
With this fix, the patch is; Reviewed-by: Emil Velikov emil.l.velikov@gmail.com
-Emil