[X2go-User] Printing Security

[senrabdet at aol.com]

Hi All - 


There is a post on the new site re printing security (see below).  Does anyone have experience with Possible Solution 1?  We're hoping to get a few more pointers, maybe some extra documentation, some "here's how you avoid these pitfalls".  Thanks!




X2goServer == CUPS Server, latest implementation (as of 20110909):

cups-x2go CUPS backend runs as root

as root the backend launches x2goprint (without sudo!!!)

x2goprint script changes owner ship of PDF file and pushes it into SSHFS share towards the X2go client.

using X2go printing locally (X2go server == CUPS server) then security (sudo) is not an issue any more(?)

Nope still is (not a big one, though): Using CUPS the user can easily be faked, allowing to fill someone else's quota or print at their home printer.




X2goServer != CUPS Server:

The Cups-server connects the x2go-Server as x2goprint-user using ssh-key auth.

x2goprint-user executes sudo to change the ownership of the PDF file and pushes it into SSHFS share towards the X2go client.

This script can currently be exploited.

If someone becomes x2goprint he might become root.




Possible solution 1


Start a local cups-server for every user

Server listens on a File-socket owned by the user

Add a PDF-Printer to that server (as the cups-user runs as that user, there should be no issues with file permissions)

Import printers from global server

+ Secure solution, as no other user is involved

- Every user needs an extra instance (The extra memory usage should not be too much)


Possible solution 2


Write a simple C-Program 'x2goprinter' that is run as the user who wants to print unsing the s-Bit

The Program writes stdin to argv[1] in the printing-directory

It also checks whether the user is x2goprint or root

+ Can be easily adopted

- x2goprint must be installed by the client

- s-bit → Needs security checks










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