1 files changed, 29 insertions, 0 deletions
diff --git a/Utility/SshHost.hs b/Utility/SshHost.hs
new file mode 100644
index 000000000..d8a8da11d
--- /dev/null
+++ b/Utility/SshHost.hs
@@ -0,0 +1,29 @@
+{- ssh hostname sanitization
+ -
+ - When constructing a ssh command with a hostname that may be controlled
+ - by an attacker, prevent the hostname from starting with "-",
+ - to prevent tricking ssh into arbitrary command execution via
+ - eg "-oProxyCommand="
+ -
+ - Copyright 2017 Joey Hess <id@joeyh.name>
+ -
+ - License: BSD-2-clause
+ -}
+
+module Utility.SshHost (SshHost, mkSshHost, fromSshHost) where
+
+newtype SshHost = SshHost String
+
+-- | Smart constructor for a legal hostname or IP address.
+-- In some cases, it may be prefixed with "user@" to specify the remote
+-- user at the host.
+--
+-- For now, we only filter out the problem ones, because determining an
+-- actually legal hostnames is quite complicated.
+mkSshHost :: String -> Either String SshHost
+mkSshHost h@('-':_) = Left $
+	"rejecting ssh hostname that starts with '-' : " ++ h
+mkSshHost h = Right (SshHost h)
+
+fromSshHost :: SshHost -> String
+fromSshHost (SshHost h) = h