luci-mod-admin-full: show also sha256 checksum for sysupgrade images

Show also the sha256 checksum in addition to MD5 checksum to enable
image verification also for builds with only sha256 checksums.

If the 'sha256sum' command is not present in the system, the value
remains empty.

Note: The easiest way to get the 'sha256sum' command is to compile it
into busybox.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

modules/luci-mod-admin-full/luasrc/controller/admin/system.lua

@@ -185,6 +185,10 @@ local function image_checksum(image)
 	return (luci.sys.exec("md5sum %q" % image):match("^([^%s]+)"))
 end
 
+local function image_sha256_checksum(image)
+	return (luci.sys.exec("sha256sum %q" % image):match("^([^%s]+)"))
+end
+
 local function supports_sysupgrade()
 	return nixio.fs.access("/lib/upgrade/platform.sh")
 end
@@ -268,6 +272,7 @@ function action_sysupgrade()
 		if image_supported(image_tmp) then
 			luci.template.render("admin_system/upgrade", {
 				checksum = image_checksum(image_tmp),
+				sha256ch = image_sha256_checksum(image_tmp),
 				storage  = storage_size(),
 				size     = (fs.stat(image_tmp, "size") or 0),
 				keep     = (not not http.formvalue("keep"))

modules/luci-mod-admin-full/luasrc/view/admin_system/upgrade.htm

@@ -24,7 +24,8 @@
 
 <fieldset class="cbi-section">
 	<ul>
-		<li><%:Checksum%>: <code><%=checksum%></code></li>
+		<li><%:Checksum MD5%>: <code><%=checksum%></code></li>
+		<li><%:Checksum SHA256%>: <code><%=sha256ch%></code></li>
 		<li><%:Size%>: <%
 			local w = require "luci.tools.webadmin"
 			write(w.byte_format(size))