[mhogomchungu]

There are "standard practices" when it comes to usage of the mount tool and TrueCrypt does not follow them and its inability to follow them is what leads to this privilege escalation.

Another "standard practice" TrueCrypt is not following is its creation of the mount point with 0777 permissions at "/media",a directory that is world readable.A "standard practice" is to have mount points at "/run/media/$USER" or "/media/$USER" or anywhere else where only the owner of the mount point has access to it.This is another security issue that need to be addressed.

[simoncion]

Everywhere I look to see how to use TrueCrypt on Linux, I see it being used as just another encrypted block device. This strongly indicates that any policy issues that you're bringing up aren't the fault of TrueCrypt, but rather are issues with whatever mount scripts you're using.

Can you point me to some documentation that would give me cause to believe otherwise?

[mhogomchungu]

What steps are involved when mounting a TrueCrypt volume?

This is what happens when you mount a TrueCrypt volume using their GUI application in linux.

1. A TrueCrypt volume is unlocked by TrueCrypt.

2. The unlocked volume is mounted by TrueCrypt.

The mounting "script" in this case is TrueCrypt and hence it is TrueCrypt's fault.

If you unlock the volume using TrueCrypt and then mount the unlocked volume using udisks,then it would be udisks' fault.

If you unlock the volume using TrueCrypt and then mount the volume yourself,then it will be your fault.

The fault is in the person who is doing the mounting and in TrueCrypt's GUI application case,TrueCrypt is the one who is doing the mounting and hence its TrueCrypt's fault.

How are you using TrueCrypt GUI if TrueCrypt is not the part that does the mounting?

I am not aware of any documentations but i am aware of discussions around "best practices" when it comes to usage of the mount command.

[simoncion]

> How are you using TrueCrypt GUI if TrueCrypt is not the part that does the mounting?

There's a GUI? Huh. Then, then answer to your question is "I'm not using the TrueCrypt GUI.".

This documentation is pretty representative of what I've been seeing (and what has worked for me) when I've looked in to using TrueCrypt on Linux:

http://www.gentoo-wiki.info/TrueCrypt

> The mounting "script" in this case is TrueCrypt and hence it is TrueCrypt's fault.

I was completely unaware of the existence of a TrueCrypt GUI. I understood TrueCrypt to be the block device encryption software that filled the same role as LUKS.

So, you should refine your claim. Rather than saying "TrueCrypt mounts things insecurely." say "There are helper scripts distributed with TrueCrypt that mount things insecurely. They should be fixed.".

> I am aware of discussions around "best practices" when it comes to usage of the mount command.

The thing about Best Practices is that they don't work in all circumstances. If the volume mounting scripts packaged with TrueCrypt get updated, any defaults should be configurable, as there exist folks who need suid binaries in their TC volumes, as well as folks who don't like mounting things in /run . :)

[mhogomchungu]

It sounds like you are trying to deflect the fault away from TrueCrypt.I looked at the link you provided and i opened a TrueCrypt volume with this command:

[root@mtz zc]# truecrypt ./rrr.img ../ink -p xxx

[root@mtz zc]#

So i opened it from the command line,i looked at the mounted volume and it was also mounted without "nosuid" option and hence the same problematic behavior is there even when TrueCrypt is used from the terminal.

Even when using the CLI component,TrueCrypt automatically does the mounting and hence its TrueCrypt's fault.

The mounting part is not done by a third party script that just happen to be bundled with TrueCrypt,it is done as a core part of TrueCrypt.The "mount" command is set here[1] and executed here[2]. You can walk up the code path to see where the "nosuid" options should have been set but isnt.

Its kind of hard to follow discussions here so if you want to take this further then respond to my email address at mhogomchungu at Gmail Dot com

[1] https://github.com/CipherShed/CipherShed/blob/e8529e95d89d3f...

[2] https://github.com/CipherShed/CipherShed/blob/e8529e95d89d3f...

ps: ciphershed is a TrueCrypt fork.You can look up TrueCrypt's original source code if you dont trust the link i gave as i couldnt find easily taggable TrueCrypt source code online

[simoncion]

There's a reason why I've not included my email address in my HN profile. I'll keep the discussion here. :)

So, if you check the truecrypt manpage [0] (or the code in that GH repo that you linked to) you'll see the presence of the --mount-options option. This allows you to pass along any and all options to mount(8) that you wish to pass along... including nosuid.

The problem you're describing isn't in TrueCrypt the crypto software, it's in its mount(8) wrapper code. TC behaves as block device encryption software, with a wrapper around mount(8) to handle volume mounting, if you want to also mount those volumes. The wrapper around mount behaves exactly as it should... which is that its defaults are the same defaults as mount, and it provides you options (through --mount-options) to change those defaults, by passing those options to mount.

Any other behavior would violate expectations and, thus be grossly incorrect. If you're concerned about others passing you a backdoor flagged with the suid bit, then the TrueCrypt authors gave you a method to mount all TC volumes with the nosuid option set by default. (And, if you're really concerned about the scenario that you outlined, you need a wrapper around mount, anyway, as ALL filesystems that support suid-flagged binaries are "vulnerable" to this "attack".)

TC doesn't need to be changed because of this. :)

[0] http://www.irongeek.com/i.php?page=backtrack-3-man/truecrypt

[mhogomchungu]

Imagine yourself a linux lab operator at a university somewhere and TrueCrypt is installed in the lab computers for students to use to access their TrueCrypt volumes.Most students will expect to have access to TrueCrypt,the GUI application as that is how most people use TrueCrypt.

Now,how exactly can you set up TrueCrypt so that a student could not use it to get root shell as i specified?.

Simple answer,you cant.

Yes,TrueCrypt gives you an option to pass the "nosuid" option.But thats like having a system that requires a password but gives you an option to not provide it with the default behavior being the option of not providing it.

The student who will sit on that computer lab with a TrueCrypt GUI window open will be the one who gets to decide if they want to set the option or not and with the option being off by default,the student will just execute the exploit without changing anything.

I should also say that i am mhogomchungu,the founder of zuluCrypt[1] that does block device encryption and also general purpose mounting with zuluMount,a tool that ships with zuluCrypt and hence i have looked at this problem very closely and for years now and i have closely followed how other FOSS projects reason with problems associated with mount command usage and their implementations to work around the problems.There are also other bunch or wrongs that TrueCrypt is doing and i know this from looking at how things are implemented "from inside" and not how they appear from outside.

Somebody using zuluCrypt to gain root shell and i will take full responsibility for it,somebody use udisks to get root shell access and i will place responsibility fully on udisks and i am fairly certain they will do the same.

[1] https://code.google.com/p/zulucrypt/

[x1798DE]

>If the volume mounting scripts packaged with TrueCrypt get updated

To be clear, it would be a serious coup if this happened in TrueCrypt itself. The developers have made it very clear that TrueCrypt is now an abandoned project. They've expressed a preference that no one fork it, but there will almost certainly be a "pseudo-fork" programmed using TC as reference code.

I suppose it's fine to use "Updating TrueCrypt" as a sort of shorthand for "change this in the pseudo-fork", I just wanted to make it clear that during the gap between TrueCrypt and whatever its successor will be, it's best to focus on mitigation strategies for vulnerabilities.

[simoncion]

Yeah. TC development has been halted. I'm aware of that. :)

The issue that the grand-parent describes isn't an issue. TC passes along mount options to mount(8). Its mount defaults are the same as mount's defaults, and TC provides a mechanism to pass along other user-specified mount options directly to mount. It makes just as much sense to complain to the TC authors about this issue as it does to complain to Ted Ts'o about the exact same "issue" in ext4, or Chris Mason about the same in Btrfs. :)