rbd: rework rbd_img_obj_exists_submit() error paths

- don't put obj_request before rbd_obj_request_get() if
  rbd_obj_request_create() fails
- don't leak pages if rbd_obj_request_create() fails
- don't leak stat_request if rbd_osd_req_create() fails

Reported-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: David Disseldorp <ddiss@suse.de>

drivers/block/rbd.c

@@ -2894,11 +2894,23 @@ static int rbd_img_obj_exists_submit(struct rbd_obj_request *obj_request)
 {
 	struct rbd_device *rbd_dev = obj_request->img_request->rbd_dev;
 	struct rbd_obj_request *stat_request;
-	struct page **pages = NULL;
+	struct page **pages;
 	u32 page_count;
 	size_t size;
 	int ret;
 
+	stat_request = rbd_obj_request_create(obj_request->object_name, 0, 0,
+					      OBJ_REQUEST_PAGES);
+	if (!stat_request)
+		return -ENOMEM;
+
+	stat_request->osd_req = rbd_osd_req_create(rbd_dev, OBJ_OP_READ, 1,
+						   stat_request);
+	if (!stat_request->osd_req) {
+		ret = -ENOMEM;
+		goto fail_stat_request;
+	}
+
 	/*
 	 * The response data for a STAT call consists of:
 	 *     le64 length;
@@ -2910,38 +2922,28 @@ static int rbd_img_obj_exists_submit(struct rbd_obj_request *obj_request)
 	size = sizeof (__le64) + sizeof (__le32) + sizeof (__le32);
 	page_count = (u32)calc_pages_for(0, size);
 	pages = ceph_alloc_page_vector(page_count, GFP_KERNEL);
-	if (IS_ERR(pages))
-		return PTR_ERR(pages);
+	if (IS_ERR(pages)) {
+		ret = PTR_ERR(pages);
+		goto fail_stat_request;
+	}
 
-	ret = -ENOMEM;
-	stat_request = rbd_obj_request_create(obj_request->object_name, 0, 0,
-							OBJ_REQUEST_PAGES);
-	if (!stat_request)
-		goto out;
+	osd_req_op_init(stat_request->osd_req, 0, CEPH_OSD_OP_STAT, 0);
+	osd_req_op_raw_data_in_pages(stat_request->osd_req, 0, pages, size, 0,
+				     false, false);
 
 	rbd_obj_request_get(obj_request);
 	stat_request->obj_request = obj_request;
 	stat_request->pages = pages;
 	stat_request->page_count = page_count;
-
-	stat_request->osd_req = rbd_osd_req_create(rbd_dev, OBJ_OP_READ, 1,
-						   stat_request);
-	if (!stat_request->osd_req)
-		goto out;
 	stat_request->callback = rbd_img_obj_exists_callback;
 
-	osd_req_op_init(stat_request->osd_req, 0, CEPH_OSD_OP_STAT, 0);
-	osd_req_op_raw_data_in_pages(stat_request->osd_req, 0, pages, size, 0,
-					false, false);
 	rbd_osd_req_format_read(stat_request);
 
 	rbd_obj_request_submit(stat_request);
 	return 0;
 
-out:
-	if (ret)
-		rbd_obj_request_put(obj_request);
-
+fail_stat_request:
+	rbd_obj_request_put(stat_request);
 	return ret;
 }