Rework authentication system

The validity of authentication tokens was determined by the
mtime of respective authentication tokens on filesystem
stored in $sessionpath.
Talking about hardware without RTC or without a prior
connection to a time server, date/time usually around 1970 -
so is the mtime of the authentication token file in
$sessionpath.

When now configuring an internet connection via LuCI, the
system might fetch the current date/time (e.g. via ntp)
which invalidates the token, returns "403 Forbidden" and
kicks the user out of the interface.

This patch changes the authentication system to use time values
based on the uptime of the machine - rather than values based upon
gettimeofday() and {a|m}time values - and save them inside the token.
That way can always determine the difference between login
(last interaction respectively) and the current time, in-
dependant of the system clock jumping backwards/forwards.

Warning: This patch removes the clean() function and respective calls.
This means, invalid tokens will NOT be determined and removed from
filesystem automatically anymore.
Before, every HTTP-call caused a scan for invalid tokens,
which is quite expensive. Instead consider using a cron job
deleting all stalled files periodically.

Contributed by T-Labs, Deutsche Telekom Innovation Laboratories

Signed-off-by: Mirko Vogt <mirko@openwrt.org>

1 files changed, 55 insertions, 40 deletions

diff --git a/libs/web/luasrc/sauth.lua b/libs/web/luasrc/sauth.lua
index 41681ab16..ef9fa1e32 100644
--- a/libs/web/luasrc/sauth.lua
+++ b/libs/web/luasrc/sauth.lua
@@ -26,36 +26,62 @@ luci.config.sauth = luci.config.sauth or {}
 sessionpath = luci.config.sauth.sessionpath
 sessiontime = tonumber(luci.config.sauth.sessiontime) or 15 * 60
 
---- Manually clean up expired sessions.
-function clean()
-	local now   = os.time()
-	local files = fs.dir(sessionpath)
-	
-	if not files then
-		return nil
-	end
-	
-	for file in files do
-		local fname = sessionpath .. "/" .. file
-		local stat = fs.stat(fname)
-		if stat and stat.type == "reg" and stat.mtime + sessiontime < now then
-			fs.unlink(fname)
-		end 
-	end
-end
-
 --- Prepare session storage by creating the session directory.
 function prepare()
 	fs.mkdir(sessionpath, 700)
-	 
 	if not sane() then
 		error("Security Exception: Session path is not sane!")
 	end
 end
 
+function encode(t)
+	return luci.util.get_bytecode({
+		user=t.user,
+		token=t.token,
+		secret=t.secret,
+		atime=luci.sys.uptime()
+	})
+end
+
+function decode(blob)
+	local t = loadstring(blob)()
+	return {
+		user = t.user,
+		token = t.token,
+		secret = t.secret,
+		atime = t.atime
+	}
+end
+
 --- Read a session and return its content.
 -- @param id	Session identifier
 -- @return		Session data
+local function _read(id)
+	local blob = fs.readfile(sessionpath .. "/" .. id)
+	return blob
+end
+
+--- Write session data to a session file.
+-- @param id	Session identifier
+-- @param data	Session data
+local function _write(id, data)
+	local f = nixio.open(sessionpath .. "/" .. id, "w", 600)
+	f:writeall(data)
+	f:close()
+end
+
+function write(id, data)
+	if not sane() then
+		prepare()
+	end
+
+	if not id or #id == 0 or not id:match("^%w+$") then
+		error("Session ID is not sane!")
+	end
+
+	_write(id, data)
+end
+
 function read(id)
 	if not id or #id == 0 then
 		return
@@ -63,12 +89,19 @@ function read(id)
 	if not id:match("^%w+$") then
 		error("Session ID is not sane!")
 	end
-	clean()
 	if not sane(sessionpath .. "/" .. id) then
 		return
 	end
-	fs.utimes(sessionpath .. "/" .. id)
-	return fs.readfile(sessionpath .. "/" .. id)
+
+	local blob = _read(id)
+	if decode(blob).atime + sessiontime < luci.sys.uptime()then
+		fs.unlink(sessionpath .. "/" .. id)
+		return
+	end
+	-- refresh atime in session
+	refreshed = encode(decode(blob))
+	write(id, refreshed)
+	return blob
 end
 
 
@@ -81,24 +114,6 @@ function sane(file)
 			== (file and "rw-------" or "rwx------")
 end
 
-
---- Write session data to a session file.
--- @param id	Session identifier
--- @param data	Session data
-function write(id, data)
-	if not sane() then
-		prepare()
-	end
-	if not id:match("^%w+$") then
-		error("Session ID is not sane!")
-	end
-	
-	local f = nixio.open(sessionpath .. "/" .. id, "w", 600)
-	f:writeall(data)
-	f:close()
-end
-
-
 --- Kills a session
 -- @param id	Session identifier
 function kill(id)