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{- 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
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