Hi Hamish, I now know more that I want to about policykit. This will amuse Tim. :-)
> > These sessions are what loginctl(1) lists, and referred to by > > `allow_any', `allow_active', and `allow_inactive'? What two > > sessions do you have in mind where it is authorised in one, still > > needs authorising in the second, and you wonder if it should? > > Yes, that's right. So long as I have only active allowed, if I run my > script with pkexec in one terminal window and authenticate, and then > open a new window (creating a new session), I have to re-authenticate > in that window. Well there we differ. loginctl(1) here doesn't list a new session for each new X terminal window. $ loginctl SESSION UID USER SEAT TTY c2 1000 ralph seat0 c73 1000 ralph seat0 2 sessions listed. $ c73 is my X session where I'm typing this, and c2 is a screen(1) that continues after I log out of X. I grep'd and found `org.freedesktop.color-manager.install-system-wide' has `auth_admin_keep' for `allow_active' so I'm using that for the test. $ pkcheck --list-temp $ pkcheck -u -a org.freedesktop.color-manager.install-system-wide -p $$ polkit\56retains_authorization_after_challenge=true polkit\56temporary_authorization_id=tmpauthz3 $ pkcheck(1) caused a GUI authentication prompt to appear and I entered my user's password. I now have a temporary authorisation that lasts five minutes. $ pkcheck --list-temp authorization id: tmpauthz3 action: org.freedesktop.color-manager.install-system-wide subject: unix-process:8351:41145575 (-bash) obtained: 4 sec ago (Thu May 17 09:35:51 2018) expires: 4 min 55 sec from now (Thu May 17 09:40:50 2018) $ I open a second X terminal and run the same command, it too sees the same existing authorisation. $ pkcheck --list-temp authorization id: tmpauthz3 action: org.freedesktop.color-manager.install-system-wide subject: unix-process:8351:41145575 (-bash) obtained: 31 sec ago (Thu May 17 09:35:51 2018) expires: 4 min 28 sec from now (Thu May 17 09:40:50 2018) $ Can you achieve something similar? > The GUI does run pkexec - to run the privileged processes it requires > to get the work done - it's a GUI for GNU ddrescue. I worded that > badly - what I'm concerned about is that all I can do right now is > check that "DDRescue-GUI.py" (the name of the GUI) is in the process > list. Someone could intentionally write a python script with that name > to fool the pkexec wrapper into doing something when it shouldn't - I > don't want it to do anything if the GUI isn't running, to prevent > security issues. I don't think you have that choice, and it's the wrong way of looking at things. You've provided a non-GUI wrapper command to run ddrescue(1) called runasroot_linux.sh. (I'd recommend dropping the `.sh' suffix.) Have you written the XML shenanigans to define an `<action>', e.g. `id=org.hamish.runasroot_linux.sh', with an `<annotation>' like <annotate key="org.freedesktop.policykit.exec.path">/usr/local/bin/runasroot_linux.sh</annotate> pkexec(1) will take the program it's asked to run and use its path to search all `<action>'s for an `<annotation>' with a key of `org.freedesktop.policykit.exec.path' that matches. That `<action>' is then used, e.g. to define how the user must authenticate. https://cgit.freedesktop.org/polkit/tree/src/programs/pkexec.c#n268 Once you've done that, your Python GUI can run `pkexec runasroot_linux.sh some args'. I think pkexec will find it in /usr/local/bin, say, due to $PATH and then search the `<action>'s. But my shell script can also do `pkexec runasroot_linux.sh other args' to make use of the service you've provided. This is intentional. There is no security in insisting only your GUI makes use of runasroot_linux.sh, and it's hard to achieve, as you're aware. If you're concerned that I can do `pkexec runasroot_linux.sh some nefarious command' and your org.hamish.runasroot_linux.sh policy will be used when it's nothing to do with ddrescue(1) then the problem is your runasroot_linux.sh. The name gives it away. You've a `do anything I throw at you' mechanism with a policy that only applies for ddrescue-ing. The script needs to only allow the limited ddrescue operations you want. If it helps, there's also a `org.freedesktop.policykit.exec.argv1' annotation that further restricts the search above to those where the first argument to the command matches. I expect this is to allow a lower bar for running `ddrescue-wrapper list' to `ddrescue-wrapper format', for example. Cheers, Ralph. -- Next meeting: Bournemouth, Tuesday, 2018-06-05 20:00 Meets, Mailing list, IRC, LinkedIn, ... http://dorset.lug.org.uk/ New thread: mailto:dorset@mailman.lug.org.uk / CHECK IF YOU'RE REPLYING Reporting bugs well: http://goo.gl/4Xue / TO THE LIST OR THE AUTHOR