lib: bpf_legacy: fix potential NULL-pointer dereference

If bpf_map_fetch_name() returns NULL, strlen() hits a NULL-pointer
dereference on outer_map_name.

Fix this checking outer_map_name value, and returning false when NULL,
as already done for inner_map_name before.

Fixes: 6d61a2b557 ("lib: add libbpf support")
Signed-off-by: Andrea Claudi <aclaudi@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

lib/bpf_legacy.c

@@ -3298,6 +3298,9 @@ bool iproute2_is_map_in_map(const char *libbpf_map_name, struct bpf_elf_map *ima
 
 			*omap = ctx->maps[j];
 			outer_map_name = bpf_map_fetch_name(ctx, j);
+			if (!outer_map_name)
+				return false;
+
 			memcpy(omap_name, outer_map_name, strlen(outer_map_name) + 1);
 
 			return true;