[PATCH] drm: limit property blob creation per file

[Xiao Kan <814091656@qq.com>]

DRM_IOCTL_MODE_CREATEPROPBLOB allows userspace to create property blobs
whose lifetime is scoped to a drm_file.

Currently, a single drm_file may create an unbounded number of blobs.
Repeated ioctl calls can trigger unbounded kernel memory allocation and
lead to OOM, resulting in a denial-of-service.

Introduce a per-drm_file limit on the number of user-created property
blobs. The limit is enforced at the point where a blob becomes associated
with a drm_file, matching the existing ownership and lifetime model.
This bounds per-file allocations while the total number of DRM file
descriptors remains constrained by existing kernel limits.

Signed-off-by: Xiao Kan <814091656@qq.com>
Signed-off-by: Xiao Kan <xiao.kan@samsung.com>
---
 drivers/gpu/drm/drm_file.c     | 1 +
 drivers/gpu/drm/drm_property.c | 8 ++++++++
 include/drm/drm_file.h         | 6 ++++++
 3 files changed, 15 insertions(+)

diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index eebd1a05e..873bf6248 100755
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -152,6 +152,7 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor)
 	INIT_LIST_HEAD(&file->fbs);
 	mutex_init(&file->fbs_lock);
 	INIT_LIST_HEAD(&file->blobs);
+	file->blob_count = 0;
 	INIT_LIST_HEAD(&file->pending_event_list);
 	INIT_LIST_HEAD(&file->event_list);
 	init_waitqueue_head(&file->event_wait);
diff --git a/drivers/gpu/drm/drm_property.c b/drivers/gpu/drm/drm_property.c
index 596272149..00eac336a 100755
--- a/drivers/gpu/drm/drm_property.c
+++ b/drivers/gpu/drm/drm_property.c
@@ -618,6 +618,7 @@ void drm_property_destroy_user_blobs(struct drm_device *dev,
 	 */
 	list_for_each_entry_safe(blob, bt, &file_priv->blobs, head_file) {
 		list_del_init(&blob->head_file);
+		file_priv->blob_count--;
 		drm_property_blob_put(blob);
 	}
 }
@@ -864,8 +865,14 @@ int drm_mode_createblob_ioctl(struct drm_device *dev,
 	 * as only the same file_priv can remove the blob; at this point, it is
 	 * not associated with any file_priv. */
 	mutex_lock(&dev->mode_config.blob_lock);
+	if (file_priv->blob_count >= DRM_FILE_MAX_PROPBLOBS) {
+		mutex_unlock(&dev->mode_config.blob_lock);
+		drm_property_blob_put(blob);
+		return -ENOSPC;
+	}
 	out_resp->blob_id = blob->base.id;
 	list_add_tail(&blob->head_file, &file_priv->blobs);
+	file_priv->blob_count++;
 	mutex_unlock(&dev->mode_config.blob_lock);
 
 	return 0;
@@ -907,6 +914,7 @@ int drm_mode_destroyblob_ioctl(struct drm_device *dev,
 	/* We must drop head_file here, because we may not be the last
 	 * reference on the blob. */
 	list_del_init(&blob->head_file);
+	file_priv->blob_count--;
 	mutex_unlock(&dev->mode_config.blob_lock);
 
 	/* One reference from lookup, and one from the filp. */
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 115763799..211c4284f 100755
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -38,6 +38,9 @@
 
 #include <drm/drm_prime.h>
 
+/* Maximum number of user-created property blobs per drm_file */
+#define DRM_FILE_MAX_PROPBLOBS 256
+
 struct dma_fence;
 struct drm_file;
 struct drm_device;
@@ -349,6 +352,9 @@ struct drm_file {
 	 */
 	struct list_head blobs;
 
+	/* Number of property blobs owned by this file */
+	unsigned int blob_count;
+
 	/** @event_wait: Waitqueue for new events added to @event_list. */
 	wait_queue_head_t event_wait;
 
-- 
2.51.0