rsh: bound the SSH handshake

ssh.Dial applies its Timeout only to the TCP connect, so a host that
accepts the connection and then stalls the SSH handshake hangs the
sync forever. Dial with a timeout, run the handshake under a deadline,
and clear the deadline once the connection is established.

1 files changed, 18 insertions, 1 deletions

diff --git a/rsh/main.go b/rsh/main.go
index dfcea0b..68b6e49 100644
--- a/rsh/main.go
+++ b/rsh/main.go
@@ -203,7 +203,24 @@ func dial(user, host string, hostKey ssh.HostKeyCallback) (*ssh.Client, error) {
 		Timeout:         dialTimeout,
 	}
 	addr := net.JoinHostPort(host, strconv.Itoa(port))
-	return ssh.Dial("tcp", addr, cfg)
+	conn, err := net.DialTimeout("tcp", addr, dialTimeout)
+	if err != nil {
+		return nil, err
+	}
+	if err := conn.SetDeadline(time.Now().Add(dialTimeout)); err != nil {
+		conn.Close()
+		return nil, err
+	}
+	clientConn, chans, reqs, err := ssh.NewClientConn(conn, addr, cfg)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+	if err := conn.SetDeadline(time.Time{}); err != nil {
+		clientConn.Close()
+		return nil, err
+	}
+	return ssh.NewClient(clientConn, chans, reqs), nil
 }
 
 // parseTransport extracts the user, host, and remote command from the argument