avoid the dashed ssh hostname class of security holes

Security fix: Disallow hostname starting with a dash, which would get
passed to ssh and be treated an option. This could be used by an attacker
who provides a crafted ssh url (for eg a git remote) to execute arbitrary
code via ssh -oProxyCommand.

No CVE has yet been assigned for this hole.
The same class of security hole recently affected git itself,
CVE-2017-1000117.

Method: Identified all places where ssh is run, by git grep '"ssh"'
Converted them all to use a SshHost, if they did not already, for
specifying the hostname.

SshHost was made a data type with a smart constructor, which rejects
hostnames starting with '-'.

Note that git-annex already contains extensive use of Utility.SafeCommand,
which fixes a similar class of problem where a filename starting with a
dash gets passed to a program which treats it as an option.

This commit was sponsored by Jochen Bartl on Patreon.

1 files changed, 5 insertions, 1 deletions

diff --git a/Remote/Helper/Ssh.hs b/Remote/Helper/Ssh.hs
index 6dfadd117..a4d91ab92 100644
--- a/Remote/Helper/Ssh.hs
+++ b/Remote/Helper/Ssh.hs
@@ -19,13 +19,17 @@ import Remote.Helper.Messages
 import Messages.Progress
 import Utility.Metered
 import Utility.Rsync
+import Utility.SshHost
 import Types.Remote
 import Types.Transfer
 import Config
 
 toRepo :: ConsumeStdin -> Git.Repo -> RemoteGitConfig -> SshCommand -> Annex (FilePath, [CommandParam])
 toRepo cs r gc remotecmd = do
-	let host = fromMaybe (giveup "bad ssh url") $ Git.Url.hostuser r
+	let host = maybe
+		(giveup "bad ssh url")
+		(either error id . mkSshHost)
+		(Git.Url.hostuser r)
 	sshCommand cs (host, Git.Url.port r) gc remotecmd
 
 {- Generates parameters to run a git-annex-shell command on a remote