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avoid the dashed ssh hostname class of security holes

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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.
This commit is contained in:
Joey Hess 2017-08-17 22:11:31 -04:00
parent 25e55e7c2f
commit df11e54788
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GPG key ID: DB12DB0FF05F8F38
12 changed files with 106 additions and 61 deletions
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6
Remote/Helper/Ssh.hs
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@ -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