A note on my debugging tricks, for posterity…
Initially, I tried to reproduce the issue (in a VM) with a Guile or Bash
process that would be invoked from shepherd before ‘user-processes’ and
that would try to read from stdin:
--8<---------------cut here---------------start------------->8---
(simple-service 'input
shepherd-root-service-type
(list (shepherd-service
(provision '(input))
(start #~(lambda ()
(pk 'tty-before?
(current-input-port)
(isatty?
(current-input-port)))
(with-output-to-file
"/dev/tty1"
(lambda ()
(system*
#$(file-append
coreutils "/bin/ls") "-l"
"/proc/self/fd")
(with-input-from-file
"/dev/tty1"
(lambda ()
(pk 'tty?
(isatty?
(current-input-port)))
(system*
#$(file-append
coreutils "/bin/ls") "-l"
"/proc/self/fd")
(system* "/bin/sh"
"-c"
"echo read; read x; echo got
$x; read y"))))))))))
(simple-service 'wait-for-input user-processes-service-type
'(input))
--8<---------------cut here---------------end--------------->8---
For some reason, that did not reproduce the issue; ‘isatty?’ would
return true.
So I though I’d arrange to run ‘cryptsetup open --type luks’. To do
that, I copied the header of a real LUKS partition:
sudo dd if=/dev/sda2 of=/tmp/luks.img bs=1024 count=1025
and then came up with an OS config that would try to open than fake LUKS
device:
(use-modules (gnu))
(use-service-modules networking ssh shepherd)
(use-package-modules base linux screen ssh)
(operating-system
(host-name "komputilo")
(timezone "Europe/Berlin")
(locale "en_US.utf8")
;; Boot in "legacy" BIOS mode, assuming /dev/sdX is the
;; target hard disk, and "my-root" is the label of the target
;; root file system.
(bootloader (bootloader-configuration
(bootloader grub-bootloader)
(targets '("/dev/sdX"))))
(mapped-devices (list (mapped-device
(source "/dev/loop0")
(target "root")
(type luks-device-mapping))))
(file-systems (cons (file-system
(device (file-system-label "my-root"))
(mount-point "/")
(type "ext4"))
%base-file-systems))
;; This is where user accounts are specified. The "root"
;; account is implicit, and is initially created with the
;; empty password.
(users (cons (user-account
(name "alice")
(comment "Bob's sister")
(group "users")
;; Adding the account to the "wheel" group
;; makes it a sudoer. Adding it to "audio"
;; and "video" allows the user to play sound
;; and access the webcam.
(supplementary-groups '("wheel"
"audio" "video")))
%base-user-accounts))
;; Globally-installed packages.
(packages (cons screen %base-packages))
;; Add services to the baseline: a DHCP client and
;; an SSH server.
(services (append (list (service dhcp-client-service-type)
(simple-service 'losetup activation-service-type
#~(system*
#$(file-append util-linux
"/sbin/losetup")
"/dev/loop0"
#$(local-file "/tmp/luks.img")))
(service openssh-service-type
(openssh-configuration
(openssh openssh-sans-x)
(port-number 2222))))
%base-services)))
That’s enough to see whether ‘cryptsetup open’ manages to read the
passphrase and all.
Eventually I confirmed by testing it on the bare metal, on a victim’s
laptop.
Currently we don’t have an installation test with cleartext root +
encrypted home; we should prolly do that.
Ludo’.
