tools/bpftool: Fix segfault case regarding 'pin' arguments

Arguments of 'pin' subcommand should be checked
at the very beginning of do_pin_any().
Otherwise segfault errors can occur when using
'map pin' or 'prog pin' commands, so fix it.

  # bpftool prog pin id
  Segmentation fault

Fixes: 71bb428fe2c1 ("tools: bpf: add bpftool")
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reported-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/common.c

@@ -217,6 +217,14 @@ int do_pin_any(int argc, char **argv, int (*get_fd_by_id)(__u32))
 	int err;
 	int fd;
 
+	if (argc < 3) {
+		p_err("too few arguments, id ID and FILE path is required");
+		return -1;
+	} else if (argc > 3) {
+		p_err("too many arguments");
+		return -1;
+	}
+
 	if (!is_prefix(*argv, "id")) {
 		p_err("expected 'id' got %s", *argv);
 		return -1;
@@ -230,9 +238,6 @@ int do_pin_any(int argc, char **argv, int (*get_fd_by_id)(__u32))
 	}
 	NEXT_ARG();
 
-	if (argc != 1)
-		usage();
-
 	fd = get_fd_by_id(id);
 	if (fd < 0) {
 		p_err("can't get prog by id (%u): %s", id, strerror(errno));