close off newline injection attacks against compute special remote protocol

Remote/Compute.hs

@@ -56,6 +56,7 @@ import Utility.CopyFile
 import Types.Key
 import Backend
 import qualified Git
+import qualified Utility.OsString as OS
 import qualified Utility.FileIO as F
 import qualified Utility.RawFilePath as R
 import qualified Utility.SimpleProtocol as Proto
@@ -271,7 +272,9 @@ formatComputeState' mk st = renderQuery False $ concat
 parseComputeState :: Key -> B.ByteString -> Maybe ComputeState
 parseComputeState k b =
 	let st = go emptycomputestate (parseQuery b)
-	in if st == emptycomputestate then Nothing else Just st
+	in if st == emptycomputestate || illegalComputeState st
+		then Nothing
+		else Just st
   where
 	emptycomputestate = ComputeState 
 		{ computeParams = mempty
@@ -317,6 +320,20 @@ parseComputeState k b =
 			_ -> Nothing
 		in go c' rest
 
+{- This is used to avoid ComputeStates that should never happen,
+ - but which could be injected into a repository by an attacker. -}
+illegalComputeState :: ComputeState -> Bool
+illegalComputeState st
+	-- The protocol is line-based, so filenames used in it cannot
+	-- contain newlines.
+	| any containsnewline (M.keys (computeInputs st)) = True
+	| any containsnewline (M.keys (computeOutputs st)) = True
+	-- Just in case.
+	| containsnewline (computeSubdir st) = True
+	| otherwise = False
+  where
+	containsnewline p = unsafeFromChar '\n' `OS.elem` p
+
 {- A compute: url for a given output file of a computation. -}
 computeStateUrl :: Remote -> ComputeState -> OsPath -> URLString
 computeStateUrl r st p = 

doc/todo/compute_special_remote_remaining_todos.mdwn

@@ -1,10 +1,6 @@
 This is the remainder of my todo list while I was building the
 compute special remote. --[[Joey]]
 
-* prohibit using compute states where an input or output filename contains
-  a newline. The protocol doesn't allow this to happen usually, but an 
-  attacker might try it in order to scramble the protocol.
-
 * git-annex responds to each INPUT immediately, and flushes stdout.
   This could cause problems if the program is sending several INPUT
   first, before reading responses, as is documented it should do to allow