webapp: Avoid crashing when ssh-keygen -F chokes on an invalid known_hosts file.

1 files changed, 5 insertions, 1 deletions

diff --git a/Assistant/Ssh.hs b/Assistant/Ssh.hs
index 876f85466..59ed34497 100644
--- a/Assistant/Ssh.hs
+++ b/Assistant/Ssh.hs
@@ -223,6 +223,10 @@ knownHost :: Text -> IO Bool
 knownHost hostname = do
 	sshdir <- sshDir
 	ifM (doesFileExist $ sshdir </> "known_hosts")
-		( not . null <$> readProcess "ssh-keygen" ["-F", T.unpack hostname]
+		( not . null <$> checkhost
 		, return False
 		)
+	where
+		{- ssh-keygen -F can crash on some old known_hosts file -}
+		checkhost = catchDefaultIO "" $
+			readProcess "ssh-keygen" ["-F", T.unpack hostname]