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[Launchpad Bug Tracker <1879980@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package cryptsetup - 2:2.2.2-3ubuntu2.3

---------------
cryptsetup (2:2.2.2-3ubuntu2.3) focal; urgency=medium

  * Introduce retry logic for external invocations after mdadm (LP: #1879980)
    - Currently, if an encrypted rootfs is configured on top of a MD RAID1
      array and such array gets degraded (e.g., a member is removed/failed)
      the cryptsetup scripts cannot mount the rootfs, and the boot fails.
      We fix that issue here by allowing the cryptroot script to be re-run
      by initramfs-tools/local-block stage, as mdadm can activate degraded
      arrays at that stage.
      There is an initramfs-tools counter-part for this fix, but alone the
      cryptsetup portion is harmless.
    - d/cryptsetup-initramfs.install: ship the new local-bottom script.
    - d/functions: declare variables for local-top|block|bottom scripts
      (flag that local-block is running and external invocation counter.)
    - d/i/s/local-block/cryptroot: set flag that local-block is running.
    - d/i/s/local-bottom/cryptroot: clean up the flag and counter files.
    - d/i/s/local-top/cryptroot: change the logic from just waiting 180
      seconds to waiting 5 seconds first, then allowing initramfs-tools
      to run mdadm (to activate degraded arrays) and call back at least
      30 times/seconds more.

 -- gpiccoli@xxxxxxxxxxxxx (Guilherme G. Piccoli)  Wed, 16 Sep 2020
17:40:05 -0300

** Changed in: cryptsetup (Ubuntu Focal)
       Status: Fix Committed => Fix Released

** Changed in: cryptsetup (Ubuntu Bionic)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1879980

Title:
  Fail to boot with LUKS on top of RAID1 if the array is broken/degraded

Status in cryptsetup package in Ubuntu:
  Fix Released
Status in initramfs-tools package in Ubuntu:
  Fix Released
Status in mdadm package in Ubuntu:
  Opinion
Status in cryptsetup source package in Xenial:
  Won't Fix
Status in initramfs-tools source package in Xenial:
  Won't Fix
Status in mdadm source package in Xenial:
  Won't Fix
Status in cryptsetup source package in Bionic:
  Fix Released
Status in initramfs-tools source package in Bionic:
  Fix Released
Status in mdadm source package in Bionic:
  Opinion
Status in cryptsetup source package in Focal:
  Fix Released
Status in initramfs-tools source package in Focal:
  Fix Released
Status in mdadm source package in Focal:
  Opinion
Status in cryptsetup source package in Groovy:
  Fix Released
Status in initramfs-tools source package in Groovy:
  Fix Released
Status in mdadm source package in Groovy:
  Opinion
Status in cryptsetup package in Debian:
  New

Bug description:
  [Impact]
  * Considering a setup of a encrypted rootfs on top of md RAID1 device, Ubuntu is currently unable to decrypt the rootfs if the array gets degraded, like for example if one of the array's members gets removed.

  * The problem has 2 main aspects: first, cryptsetup initramfs script
  attempts to decrypt the array only in the local-top boot stage, and in
  case it fails, it gives-up and show user a shell (boot is aborted).

  * Second, mdadm initramfs script that assembles degraded arrays
  executes later on boot, in the local-block stage. So, in a stacked
  setup of encrypted root on top of RAID, if the RAID is degraded,
  cryptsetup fails early in the boot, preventing mdadm to assemble the
  degraded array.

  * The hereby proposed solution has 2 components: first, cryptsetup
  script is modified to allow a gentle failure on local-top stage, then
  it retries for a while (according to a heuristic based on ROOTDELAY
  with minimum of 30 executions) in a later stage (local-block). This
  gives time to other initramfs scripts to run, like mdadm in local-
  block stage. And this is meant to work this way according to
  initramfs-tools documentation (although Ubuntu changed it a bit with
  wait-for-root, hence we stopped looping on local-block, see next
  bullet).

  * Second, initramfs-tools was adjusted - currently, it runs for a
  while the mdadm local-block script, in order to assemble the arrays in
  a non-degraded mode. We extended this approach to also execute
  cryptsetup, in a way that after mdadm ends its execution, we execute
  at least once more time cryptsetup. In an ideal world we should loop
  on local-block as Debian's initramfs (in a way to remove hardcoded
  mdadm/cryptsetup mentions from initramfs-tools code), but this would
  be really a big change, non-SRUable probably. I plan to work that for
  future Ubuntu releases.

  [Test case]
  * Install Ubuntu in a Virtual Machine with 2 disks. Use the installer to create a RAID1 volume and an encrypted root on top of it.

  * Boot the VM, and use "sgdisk"/"wipefs" to erase the partition table
  from one of the RAID members. Reboot and it will fail to mount rootfs
  and continue boot process.

  * If using the initramfs-toos/cryptsetup patches hereby proposed, the
  rootfs can be mounted normally.

  [Regression potential]

  * There are potential for regressions, since this is a change in 2
  boot components. The patches were designed in a way to keep the
  regular case working, it changes the failure case which is not
  currently working anyway.

  * A modification in the behavior of cryptsetup was introduced: right
  now, if we fail the password 3 times (the default maximum attempts),
  the script doesn't "panic" and drop to a shell immediately; instead it
  runs once more (or twice, if mdadm is installed) before failing. This
  is a minor change given the benefit of the being able to mount rootfs
  in a degraded RAID1 scenario.

  * Other potential regressions could show-up as boot problems, but the
  change in initramfs-tools specifically is not invasive, it just may
  delay boot time a bit, given we now run cryptsetup multiple times on
  local-block, with 1 sec delays between executions.

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