libbpf: Close map fd if init map slots failed

Previously we forgot to close the map fd if bpf_map_update_elem()
failed during map slot init, which will leak map fd.

Let's move map slot initialization to new function init_map_slots() to
simplify the code. And close the map fd if init slot failed.
Reported-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20201006021345.3817033-2-liuhangbin@gmail.com

tools/lib/bpf/libbpf.c

@@ -4203,6 +4203,36 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map)
 	return 0;
 }
 
+static int init_map_slots(struct bpf_map *map)
+{
+	const struct bpf_map *targ_map;
+	unsigned int i;
+	int fd, err;
+
+	for (i = 0; i < map->init_slots_sz; i++) {
+		if (!map->init_slots[i])
+			continue;
+
+		targ_map = map->init_slots[i];
+		fd = bpf_map__fd(targ_map);
+		err = bpf_map_update_elem(map->fd, &i, &fd, 0);
+		if (err) {
+			err = -errno;
+			pr_warn("map '%s': failed to initialize slot [%d] to map '%s' fd=%d: %d\n",
+				map->name, i, targ_map->name,
+				fd, err);
+			return err;
+		}
+		pr_debug("map '%s': slot [%d] set to map '%s' fd=%d\n",
+			 map->name, i, targ_map->name, fd);
+	}
+
+	zfree(&map->init_slots);
+	map->init_slots_sz = 0;
+
+	return 0;
+}
+
 static int
 bpf_object__create_maps(struct bpf_object *obj)
 {
@@ -4245,28 +4275,11 @@ bpf_object__create_maps(struct bpf_object *obj)
 		}
 
 		if (map->init_slots_sz) {
-			for (j = 0; j < map->init_slots_sz; j++) {
-				const struct bpf_map *targ_map;
-				int fd;
-
-				if (!map->init_slots[j])
-					continue;
-
-				targ_map = map->init_slots[j];
-				fd = bpf_map__fd(targ_map);
-				err = bpf_map_update_elem(map->fd, &j, &fd, 0);
-				if (err) {
-					err = -errno;
-					pr_warn("map '%s': failed to initialize slot [%d] to map '%s' fd=%d: %d\n",
-						map->name, j, targ_map->name,
-						fd, err);
-					goto err_out;
-				}
-				pr_debug("map '%s': slot [%d] set to map '%s' fd=%d\n",
-					 map->name, j, targ_map->name, fd);
+			err = init_map_slots(map);
+			if (err < 0) {
+				zclose(map->fd);
+				goto err_out;
 			}
-			zfree(&map->init_slots);
-			map->init_slots_sz = 0;
 		}
 
 		if (map->pin_path && !map->pinned) {