From 758965d177d75f529bb88e24564a0bdb5e406fc6 Mon Sep 17 00:00:00 2001
From: Joey Hess <joeyh@joeyh.name>
Date: Tue, 27 Sep 2016 20:22:53 -0400
Subject: Filter out escape sequences and any other unusual characters when
 writing all messages to the console.

This should protect against all attacks where the server sends back a
malicious message.
---
 Output.hs | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 Output.hs

(limited to 'Output.hs')

diff --git a/Output.hs b/Output.hs
new file mode 100644
index 0000000..f655d0a
--- /dev/null
+++ b/Output.hs
@@ -0,0 +1,33 @@
+-- All console output in keysafe should go via this module;
+-- avoid using putStrLn, print, etc directly.
+
+module Output (ask, progress, say, warn, display) where
+
+import System.IO
+import Data.Char
+
+ask :: String -> IO ()
+ask s = do
+	putStr (escape s)
+	hFlush stdout
+
+progress :: String -> IO ()
+progress = ask
+
+say :: String -> IO ()
+say = putStrLn . escape
+
+warn :: String -> IO ()
+warn = hPutStrLn stderr . escape
+
+display :: Show s => s -> IO ()
+display = say . show
+
+-- | Prevent malicious escape sequences etc in a string
+-- from being output to the console.
+escape :: String -> String
+escape = concatMap go
+   where
+	go c = if isPrint c || isSpace c
+		then [c]
+		else "\\" ++ show (ord c)
-- 
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