disk content permanently lost when changing LUKS password

[Will Cooke]

[Impact]

Users with full disk encryption trying to change the encryption passphrase in gnome-disks will get an error message, and after rebooting neither the old passphrase nor the new one can unlock their disk, rendering the machine unusable.

[Test Case]

(can be done in a virtual machine, for testing purposes)
1. Download a 19.04 ISO, and install it, choosing the full disk encryption option
2. When rebooting after the installation is complete, you are prompted for your passphrase to unlock the disk
3. Once logged in, open gnome-disks, select the encrypted disk and click the contextual action to change the encryption passphrase
4. Enter your old passphrase and the new one (twice), as prompted, then click OK

Expected result: the passphrase is changed successfully, and when rebooting the new passphrase can unlock the disk

Current result: changing the passphrase fails, the user is presented with an error message ("Error changing passphrase on device /dev/sda5: Failed to add the new passphrase: Invalid argument (udisks-error-quark, 0)"), and when rebooting neither the old passphrase nor the new one can unlock the disk, which renders it unusable

To test the fix, the updated libblockdev* packages need to be installed on the machine before attempting to change the encryption passphrase in gnome-disks.

[Regression Potential]

The patch only touches code related to changing the LUKS encryption passphrase, so non-encrypted disk setups should not be affected.
Scenarii with full-disk encryption should be carefully tested, including changing an existing passphrase, adding and removing passphrases, both from the gnome-disks UI and using the cryptsetup CLI.

[Original Description]

This is fixed upstream. Logging this bug to track the fix in to Ubuntu.

From the upstream bug:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=928893

Dear Maintainer,

   * What led up to the situation?

Install system using normal full disk encryption LUKS+Ext4.
After install open gnome-disk-utility and change
encryption password. It gives some error dialog and
now you are royally screwed. It deleted the only
LUKS keyslot. Cannot add new keyslots because of that.
All data will be lost after reboot.

Here is output of luksdump:

udo cryptsetup luksDump /dev/sda5
LUKS header information
Version: 2
Epoch: 4
Metadata area: 16384 [bytes]
Keyslots area: 16744448 [bytes]
UUID: 3c16ad4c-294c-4547-bf3e-bb8864ba5ea3
Label: (no label)
Subsystem: (no subsystem)
Flags: (no flags)

Data segments:
  0: crypt
        offset: 16777216 [bytes]
        length: (whole device)
        cipher: aes-xts-plain64
        sector: 512 [bytes]

Keyslots:
Tokens:
Digests:
  0: pbkdf2
        Hash: sha256
        Iterations: 59904
        Salt: XX XX XX XX XX ....
        Digest: XX XX XX XX XX ...

----------------------------------------

I changed salt and digest. No Keyslots are present!!!

I tried this 2 times in a row with new install,
exactly same result.

-- System Information:
Debian Release: buster/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.0.8-xanmod5 (SMP w/2 CPU cores; PREEMPT)
Locale: LANG=ru_RU.UTF-8, LC_CTYPE=ru_RU.UTF-8 (charmap=UTF-8), LANGUAGE=ru_RU.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages gnome-disk-utility depends on:
ii dconf-gsettings-backend [gsettings-backend] 0.30.1-2
ii libatk1.0-0 2.30.0-2
ii libc6 2.28-10
ii libcairo2 1.16.0-4
ii libcanberra-gtk3-0 0.30-7
ii libdvdread4 6.0.1-1
ii libgdk-pixbuf2.0-0 2.38.1+dfsg-1
ii libglib2.0-0 2.58.3-1
ii libgtk-3-0 3.24.5-1
ii liblzma5 5.2.4-1
ii libnotify4 0.7.7-4
ii libpango-1.0-0 1.42.4-6
ii libpangocairo-1.0-0 1.42.4-6
ii libpwquality1 1.4.0-3
ii libsecret-1-0 0.18.7-1
ii libsystemd0 241-3
ii libudisks2-0 2.8.1-4
ii udisks2 2.8.1-4

gnome-disk-utility recommends no packages.

gnome-disk-utility suggests no packages.

-- no debconf information

[Tom Reynolds (tomreyn)]

Possible Workaround (untested):
This only applies if you have not rebooted / closed the LUKS volume. Follow steps 7 to 9 of https://www.thegeekstuff.com/2016/03/cryptsetup-lukskey/

[Iain Lane (laney)]

thanks for filing

I'm guessing we should reproduce the problem, see if it happens on bionic & then backport libblockdev 2.20-7+deb10u1

[Olivier Tilloy (osomon)]

I can reliably reproduce the issue when installing 19.04 in a VM. The error message after changing the passphrase in gnome-disks is:

    Error changing passphrase

    Error changing passphrase on device /dev/sda5: Failed to add the new passphrase: Invalid argument (udisks-error-quark, 0)

    [Close]

I cannot reproduce the issue when installing 18.04.2 in a VM, so version 2.16-2 of libblockdev doesn't appear to be affected.

[Olivier Tilloy (osomon)]

I installed 19.04 in a VM with full disk encryption, then upgraded libblockdev from buster-proposed-updates (2.20-7+deb10u1), rebooted, and I was able to successfully change the passphrase in gnome-disks.

[Olivier Tilloy (osomon)]

Attaching a debdiff for a disco SRU, as I don't have upload permission for libblockdev.
Please sponsor!

[Iain Lane (laney)]

I sponsored it, thanks! (Also, Scenarii, nice)

[Brian Murray (brian-murray)]

Hello Will, or anyone else affected,

Accepted libblockdev into disco-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/libblockdev/2.20-7ubuntu0.1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-disco to verification-done-disco. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-disco. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Olivier Tilloy (osomon)]

Successfully tested by running the test case in the bug description. Without the libblockdev update, changing the LUKS encryption passphrase from gnome-disks fails. With the updated package, it succeeds (and I verified that the new passphrase unlocks the encrypted disk at boot).

I also verified that the updated package doesn't affect the normal operation of the cryptsetup CLI to change the passphrase (AFAICT cryptsetup doesn't depend on libblockdev anyway).

[Brian Murray (brian-murray)]

The verification of the Stable Release Update for libblockdev has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

[Launchpad Janitor (janitor)]

This bug was fixed in the package libblockdev - 2.20-7ubuntu0.1

---------------
libblockdev (2.20-7ubuntu0.1) disco; urgency=medium

  [ intrigeri ]
  * Use existing cryptsetup API for changing keyslot passphrase.
    Cherry-pick upstream fix to use existing cryptsetup API for atomically
    changing a keyslot passphrase, instead of deleting the old keyslot
    before adding the new one. This avoids data loss when attempting to
    change the passphrase of a LUKS2 device via udisks2, e.g. from GNOME
    Disks.
    Deleting a keyslot and then adding one is risky: if anything goes wrong
    before the new keyslot is successfully added, no usable keyslot is left
    and the device cannot be unlocked anymore. There's little chances this
    causes actual problems with LUKS1, but LUKS2 defaults to the memory-hard
    Argon2 key derivation algorithm, which is implemented in cryptsetup with
    the assumption that it runs as root with no MEMLOCK ulimit; this
    assumption is wrong when run by udisks2.service under
    LimitMEMLOCK=65536, which breaks adding the new keyslot, and makes us
    hit the problematic situation (user data loss) every time.
    With this change, changing a LUKS2 passphrase via udisks2 will still
    fail in some cases, until the MEMLOCK ulimit problem is solved in
    cryptsetup or workaround'ed in udisks2. But at least, if it fails, it
    will fail _atomically_ and the original passphrase will still work.
    (Closes: #928893) (LP: #1837437)

 -- Olivier Tilloy <email address hidden> Thu, 25 Jul 2019 12:33:46 +0200

[Walt Pritz (wpritz)]

Sorry to add to an old issue, but I can confirm the issue persists under Ubuntu 18.04.5.

I can reliably reproduce the issue when installing 18.04.5 on physical hardware, Lenovo ThinkPad P15 (20SUS5LJ00). The error message after changing the passphrase in gnome-disks is:

    Error changing passphrase

    Error changing passphrase on device /dev/nvme1n1p3: Failed to add the new passphrase: Invalid argument (udisks-error-quark, 0)

    [Close]