selftests/bpf: Check inner map deletion

Add a test case to check whether an unsuccessful creation of an outer
map of a BTF-defined map-in-map destroys the inner map.

As bpf_object__create_map() is a static function, we cannot just call it
from the test case and then check whether a map accessible via
map->inner_map_fd has been closed. Instead, we iterate over all maps and
check whether the map "$MAP_NAME.inner" does not exist.

Signed-off-by: Martynas Pumputis <m@lambda.lt>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210719173838.423148-3-m@lambda.lt

tools/testing/selftests/bpf/progs/test_map_in_map_invalid.c

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Isovalent, Inc. */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct inner {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, __u32);
+	__type(value, int);
+	__uint(max_entries, 4);
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
+	__uint(max_entries, 0); /* This will make map creation to fail */
+	__uint(key_size, sizeof(__u32));
+	__array(values, struct inner);
+} mim SEC(".maps");
+
+SEC("xdp")
+int xdp_noop0(struct xdp_md *ctx)
+{
+	return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/test_maps.c

@@ -1153,12 +1153,16 @@ out_sockmap:
 }
 
 #define MAPINMAP_PROG "./test_map_in_map.o"
+#define MAPINMAP_INVALID_PROG "./test_map_in_map_invalid.o"
 static void test_map_in_map(void)
 {
 	struct bpf_object *obj;
 	struct bpf_map *map;
 	int mim_fd, fd, err;
 	int pos = 0;
+	struct bpf_map_info info = {};
+	__u32 len = sizeof(info);
+	__u32 id = 0;
 
 	obj = bpf_object__open(MAPINMAP_PROG);
 
@@ -1228,11 +1232,68 @@ static void test_map_in_map(void)
 	}
 
 	close(fd);
+	fd = -1;
 	bpf_object__close(obj);
+
+	/* Test that failing bpf_object__create_map() destroys the inner map */
+	obj = bpf_object__open(MAPINMAP_INVALID_PROG);
+	err = libbpf_get_error(obj);
+	if (err) {
+		printf("Failed to load %s program: %d %d",
+		       MAPINMAP_INVALID_PROG, err, errno);
+		goto out_map_in_map;
+	}
+
+	map = bpf_object__find_map_by_name(obj, "mim");
+	if (!map) {
+		printf("Failed to load array of maps from test prog\n");
+		goto out_map_in_map;
+	}
+
+	err = bpf_object__load(obj);
+	if (!err) {
+		printf("Loading obj supposed to fail\n");
+		goto out_map_in_map;
+	}
+
+	/* Iterate over all maps to check whether the internal map
+	 * ("mim.internal") has been destroyed.
+	 */
+	while (true) {
+		err = bpf_map_get_next_id(id, &id);
+		if (err) {
+			if (errno == ENOENT)
+				break;
+			printf("Failed to get next map: %d", errno);
+			goto out_map_in_map;
+		}
+
+		fd = bpf_map_get_fd_by_id(id);
+		if (fd < 0) {
+			if (errno == ENOENT)
+				continue;
+			printf("Failed to get map by id %u: %d", id, errno);
+			goto out_map_in_map;
+		}
+
+		err = bpf_obj_get_info_by_fd(fd, &info, &len);
+		if (err) {
+			printf("Failed to get map info by fd %d: %d", fd,
+			       errno);
+			goto out_map_in_map;
+		}
+
+		if (!strcmp(info.name, "mim.inner")) {
+			printf("Inner map mim.inner was not destroyed\n");
+			goto out_map_in_map;
+		}
+	}
+
 	return;
 
 out_map_in_map:
-	close(fd);
+	if (fd >= 0)
+		close(fd);
 	exit(1);
 }