tools lib bpf: Check return value of strdup when reading map names

Commit 561bbccac72d08babafaa33fd7fa9100ec4c9fb6 ("tools lib bpf:
Extract and collect map names from BPF object file") forgets checking
return value of strdup(). This patch fixes it. It also checks names
pointer before strcmp() for safety.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Fixes: 561bbccac72d ("tools lib bpf: Extract and collect map names from BPF object file")
Link: http://lkml.kernel.org/r/1449541544-67621-2-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/bpf/libbpf.c

@@ -527,14 +527,14 @@ bpf_object__init_maps(struct bpf_object *obj, void *data,
 	return 0;
 }
 
-static void
+static int
 bpf_object__init_maps_name(struct bpf_object *obj, int maps_shndx)
 {
 	int i;
 	Elf_Data *symbols = obj->efile.symbols;
 
 	if (!symbols || maps_shndx < 0)
-		return;
+		return -EINVAL;
 
 	for (i = 0; i < symbols->d_size / sizeof(GElf_Sym); i++) {
 		GElf_Sym sym;
@@ -556,9 +556,14 @@ bpf_object__init_maps_name(struct bpf_object *obj, int maps_shndx)
 			continue;
 		}
 		obj->maps[map_idx].name = strdup(map_name);
+		if (!obj->maps[map_idx].name) {
+			pr_warning("failed to alloc map name\n");
+			return -ENOMEM;
+		}
 		pr_debug("map %zu is \"%s\"\n", map_idx,
 			 obj->maps[map_idx].name);
 	}
+	return 0;
 }
 
 static int bpf_object__elf_collect(struct bpf_object *obj)
@@ -663,7 +668,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 	}
 
 	if (maps_shndx >= 0)
-		bpf_object__init_maps_name(obj, maps_shndx);
+		err = bpf_object__init_maps_name(obj, maps_shndx);
 out:
 	return err;
 }
@@ -1372,7 +1377,7 @@ bpf_object__get_map_by_name(struct bpf_object *obj, const char *name)
 	struct bpf_map *pos;
 
 	bpf_map__for_each(pos, obj) {
-		if (strcmp(pos->name, name) == 0)
+		if (pos->name && !strcmp(pos->name, name))
 			return pos;
 	}
 	return NULL;