auth-filters: generate secret securely

[ps-cgit] / filters / simple-authentication.lua

diff --git a/filters/simple-authentication.lua b/filters/simple-authentication.lua
index 596c04184841eef803de918c7aab8b8e43769b87..bf356324e2b00865d727cb3e9065b094286c0a73 100644 (file)
--- 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"
 
 --
 --
@@ -191,7 +194,38 @@ 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(expected_field, cookie)
@@ -231,7 +265,7 @@ function validate_value(expected_field, cookie)
        end
 
        -- Lua hashes strings, so these comparisons are time invariant.
-       if hmac ~= crypto.hmac.digest("sha256", field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt, secret) then
+       if hmac ~= crypto.hmac.digest("sha256", field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt, get_secret()) then
                return nil
        end
 
@@ -256,7 +290,7 @@ function secure_value(field, value, expiration)
        value = url_encode(value)
        field = url_encode(field)
        authstr = field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt
-       authstr = authstr .. "|" .. crypto.hmac.digest("sha256", authstr, secret)
+       authstr = authstr .. "|" .. crypto.hmac.digest("sha256", authstr, get_secret())
        return authstr
 end