luci-base: add support for POST-only actions with CSRF token check

Add the dispatcher infrastructure to restrict certain routes to POST
requests only in conjunction with verification of CSRF tokens.

This is the first step to get rid of the CSRF token in the url in favor
to tokens embedded in forms.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

modules/luci-base/luasrc/dispatcher.lua

@@ -1,4 +1,5 @@
 -- Copyright 2008 Steven Barth <steven@midlink.org>
+-- Copyright 2008-2015 Jo-Philipp Wich <jow@openwrt.org>
 -- Licensed to the public under the Apache License 2.0.
 
 local fs = require "nixio.fs"
@@ -284,6 +285,7 @@ function dispatch(request)
 		   resource    = luci.config.main.resourcebase;
 		   ifattr      = function(...) return _ifattr(...) end;
 		   attr        = function(...) return _ifattr(true, ...) end;
+		   token       = ctx.urltoken.stok;
 		}, {__index=function(table, key)
 			if key == "controller" then
 				return build_url()
@@ -378,6 +380,20 @@ function dispatch(request)
 		end
 	end
 
+	if c and type(c.target) == "table" and c.target.post == true then
+		if http.getenv("REQUEST_METHOD") ~= "POST" then
+			http.status(405, "Method Not Allowed")
+			http.header("Allow", "POST")
+			return
+		end
+
+		if http.formvalue("token") ~= ctx.urltoken.stok then
+			http.status(403, "Forbidden")
+			luci.template.render("csrftoken")
+			return
+		end
+	end
+
 	if track.setgroup then
 		sys.process.setgroup(track.setgroup)
 	end
@@ -703,6 +719,16 @@ function call(name, ...)
 	return {type = "call", argv = {...}, name = name, target = _call}
 end
 
+function post(name, ...)
+	return {
+		type = "call",
+		post = true,
+		argv = { ... },
+		name = name,
+		target = _call
+	}
+end
+
 
 local _template = function(self, ...)
 	require "luci.template".render(self.view)

modules/luci-base/luasrc/view/csrftoken.htm

@@ -0,0 +1,24 @@
+<%#
+ Copyright 2015 Jo-Philipp Wich <jow@openwrt.org>
+ Licensed to the public under the Apache License 2.0.
+-%>
+
+<%+header%>
+
+<h2 name="content"><%:Form token mismatch%></h2>
+<br />
+
+<p class="alert-message"><%:The submitted security token is invalid or already expired!%></p>
+
+<p><%:
+	In order to prevent unauthorized access to the system, your request has
+	been blocked. Click "Continue »" below to return to the previous page.
+%></p>
+
+<hr />
+
+<p class="right">
+	<strong><a href="#" onclick="window.history.back();">Continue »</a></strong>
+</p>
+
+<%+footer%>