X-Git-Url: https://gitweb.ps.run/ps-cgit/blobdiff_plain/aa6d5b105de9de6d01855c15217e46fd36890dbc..b73df8098f261ecbd4bc5ba689f9766a1a75f9a0:/filters/simple-authentication.lua

diff --git a/filters/simple-authentication.lua b/filters/simple-authentication.lua
index cc86b7e..bf35632 100644
--- a/filters/simple-authentication.lua
+++ b/filters/simple-authentication.lua
@@ -3,7 +3,12 @@
 -- Requirements:
 -- 	luacrypto >= 0.3
 -- 	<http://mkottman.github.io/luacrypto/>
+-- 	luaposix
+-- 	<https://github.com/luaposix/luaposix>
 --
+local sysstat = require("posix.sys.stat")
+local unistd = require("posix.unistd")
+local crypto = require("crypto")
 
 
 --
@@ -31,11 +36,9 @@ local users = {
 	bob		= "ilikelua"
 }
 
--- All cookies will be authenticated based on this secret. Make it something
--- totally random and impossible to guess. It should be large.
-local secret = "BE SURE TO CUSTOMIZE THIS STRING TO SOMETHING BIG AND RANDOM"
-
-
+-- Set this to a path this script can write to for storing a persistent
+-- cookie secret, which should be guarded.
+local secret_filename = "/var/cache/cgit/auth-secret"
 
 --
 --
@@ -46,7 +49,7 @@ local secret = "BE SURE TO CUSTOMIZE THIS STRING TO SOMETHING BIG AND RANDOM"
 -- Sets HTTP cookie headers based on post and sets up redirection.
 function authenticate_post()
 	local password = users[post["username"]]
-	local redirect = validate_value(post["redirect"])
+	local redirect = validate_value("redirect", post["redirect"])
 
 	if redirect == nil then
 		not_found()
@@ -60,7 +63,7 @@ function authenticate_post()
 		set_cookie("cgitauth", "")
 	else
 		-- One week expiration time
-		local username = secure_value(post["username"], os.time() + 604800)
+		local username = secure_value("username", post["username"], os.time() + 604800)
 		set_cookie("cgitauth", username)
 	end
 
@@ -77,7 +80,7 @@ function authenticate_cookie()
 		return 1
 	end
 
-	local username = validate_value(get_cookie(http["cookie"], "cgitauth"))
+	local username = validate_value("username", get_cookie(http["cookie"], "cgitauth"))
 	if username == nil or not accepted_users[username:lower()] then
 		return 0
 	else
@@ -92,7 +95,7 @@ function body()
 	html_attr(cgit["login"])
 	html("'>")
 	html("<input type='hidden' name='redirect' value='")
-	html_attr(secure_value(cgit["url"], 0))
+	html_attr(secure_value("redirect", cgit["url"], 0))
 	html("' />")
 	html("<table>")
 	html("<tr><td><label for='username'>Username:</label></td><td><input id='username' name='username' autofocus /></td></tr>")
@@ -191,12 +194,44 @@ end
 --
 --
 
-local crypto = require("crypto")
+local secret = nil
+
+-- Loads a secret from a file, creates a secret, or returns one from memory.
+function get_secret()
+	if secret ~= nil then
+		return secret
+	end
+	local secret_file = io.open(secret_filename, "r")
+	if secret_file == nil then
+		local old_umask = sysstat.umask(63)
+		local temporary_filename = secret_filename .. ".tmp." .. crypto.hex(crypto.rand.bytes(16))
+		local temporary_file = io.open(temporary_filename, "w")
+		if temporary_file == nil then
+			os.exit(177)
+		end
+		temporary_file:write(crypto.hex(crypto.rand.bytes(32)))
+		temporary_file:close()
+		unistd.link(temporary_filename, secret_filename) -- Intentionally fails in the case that another process is doing the same.
+		unistd.unlink(temporary_filename)
+		sysstat.umask(old_umask)
+		secret_file = io.open(secret_filename, "r")
+	end
+	if secret_file == nil then
+		os.exit(177)
+	end
+	secret = secret_file:read()
+	secret_file:close()
+	if secret:len() ~= 64 then
+		os.exit(177)
+	end
+	return secret
+end
 
 -- Returns value of cookie if cookie is valid. Otherwise returns nil.
-function validate_value(cookie)
+function validate_value(expected_field, cookie)
 	local i = 0
 	local value = ""
+	local field = ""
 	local expiration = 0
 	local salt = ""
 	local hmac = ""
@@ -207,15 +242,17 @@ function validate_value(cookie)
 
 	for component in string.gmatch(cookie, "[^|]+") do
 		if i == 0 then
-			value = component
+			field = component
 		elseif i == 1 then
+			value = component
+		elseif i == 2 then
 			expiration = tonumber(component)
 			if expiration == nil then
-				expiration = 0
+				expiration = -1
 			end
-		elseif i == 2 then
-			salt = component
 		elseif i == 3 then
+			salt = component
+		elseif i == 4 then
 			hmac = component
 		else
 			break
@@ -228,18 +265,22 @@ function validate_value(cookie)
 	end
 
 	-- Lua hashes strings, so these comparisons are time invariant.
-	if hmac ~= crypto.hmac.digest("sha1", value .. "|" .. tostring(expiration) .. "|" .. salt, secret) then
+	if hmac ~= crypto.hmac.digest("sha256", field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt, get_secret()) then
+		return nil
+	end
+
+	if expiration == -1 or (expiration ~= 0 and expiration <= os.time()) then
 		return nil
 	end
 
-	if expiration ~= 0 and expiration <= os.time() then
+	if url_decode(field) ~= expected_field then
 		return nil
 	end
 
 	return url_decode(value)
 end
 
-function secure_value(value, expiration)
+function secure_value(field, value, expiration)
 	if value == nil or value:len() <= 0 then
 		return ""
 	end
@@ -247,8 +288,9 @@ function secure_value(value, expiration)
 	local authstr = ""
 	local salt = crypto.hex(crypto.rand.bytes(16))
 	value = url_encode(value)
-	authstr = value .. "|" .. tostring(expiration) .. "|" .. salt
-	authstr = authstr .. "|" .. crypto.hmac.digest("sha1", authstr, secret)
+	field = url_encode(field)
+	authstr = field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt
+	authstr = authstr .. "|" .. crypto.hmac.digest("sha256", authstr, get_secret())
 	return authstr
 end