net/9p: add privport option to 9p tcp transport

If the privport option is specified, the tcp transport binds local
address to a reserved port before connecting to the 9p server.

In some cases when 9P AUTH cannot be implemented, this is better than
nothing.

Signed-off-by: Jim Garlick <[e-mail]>
Signed-off-by: Eric Van Hensbergen <[e-mail]>

include/net/9p/transport.h

···
 #ifndef NET_9P_TRANSPORT_H
 #define NET_9P_TRANSPORT_H
 
+#define P9_DEF_MIN_RESVPORT	(665U)
+#define P9_DEF_MAX_RESVPORT	(1023U)
+
 /**
  * struct p9_trans_module - transport module interface
  * @list: used to maintain a list of currently available transports

net/9p/trans_fd.c

···
 	int rfd;
 	int wfd;
 	u16 port;
+	int privport;
 };
 
 /**
···
 enum {
 	/* Options that take integer arguments */
 	Opt_port, Opt_rfdno, Opt_wfdno, Opt_err,
+	/* Options that take no arguments */
+	Opt_privport,
 };
 
 static const match_table_t tokens = {
 	{Opt_port, "port=%u"},
 	{Opt_rfdno, "rfdno=%u"},
 	{Opt_wfdno, "wfdno=%u"},
+	{Opt_privport, "privport"},
 	{Opt_err, NULL},
 };
 
···
 static DEFINE_SPINLOCK(p9_poll_lock);
 static LIST_HEAD(p9_poll_pending_list);
 static DECLARE_WORK(p9_poll_work, p9_poll_workfn);
+
+static unsigned int p9_ipport_resv_min = P9_DEF_MIN_RESVPORT;
+static unsigned int p9_ipport_resv_max = P9_DEF_MAX_RESVPORT;
 
 static void p9_mux_poll_stop(struct p9_conn *m)
 {
···
 		if (!*p)
 			continue;
 		token = match_token(p, tokens, args);
-		if (token != Opt_err) {
+		if ((token != Opt_err) && (token != Opt_privport)) {
 			r = match_int(&args[0], &option);
 			if (r < 0) {
 				p9_debug(P9_DEBUG_ERROR,
···
 			break;
 		case Opt_wfdno:
 			opts->wfd = option;
+			break;
+		case Opt_privport:
+			opts->privport = 1;
 			break;
 		default:
 			continue;
···
 	return 0;
 }
 
+static int p9_bind_privport(struct socket *sock)
+{
+	struct sockaddr_in cl;
+	int port, err = -EINVAL;
+
+	memset(&cl, 0, sizeof(cl));
+	cl.sin_family = AF_INET;
+	cl.sin_addr.s_addr = INADDR_ANY;
+	for (port = p9_ipport_resv_max; port >= p9_ipport_resv_min; port--) {
+		cl.sin_port = htons((ushort)port);
+		err = kernel_bind(sock, (struct sockaddr *)&cl, sizeof(cl));
+		if (err != -EADDRINUSE)
+			break;
+	}
+	return err;
+}
+
+
 static int
 p9_fd_create_tcp(struct p9_client *client, const char *addr, char *args)
 {
···
 		pr_err("%s (%d): problem creating socket\n",
 		       __func__, task_pid_nr(current));
 		return err;
+	}
+
+	if (opts.privport) {
+		err = p9_bind_privport(csocket);
+		if (err < 0) {
+			pr_err("%s (%d): problem binding to privport\n",
+			       __func__, task_pid_nr(current));
+			sock_release(csocket);
+			return err;
+		}
 	}
 
 	err = csocket->ops->connect(csocket,