group.of.nepali.translators team mailing list archive

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

** Changed in: linux (Ubuntu)
       Status: Incomplete => Triaged

** Changed in: linux (Ubuntu)
   Importance: Undecided => High

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Eoan)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Disco)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1860231

Title:
  5.4.0-11 crash on cryptsetup open

Status in linux package in Ubuntu:
  Triaged
Status in linux source package in Xenial:
  New
Status in linux source package in Bionic:
  New
Status in linux source package in Disco:
  New
Status in linux source package in Eoan:
  New

Bug description:
  [Impact]

  An attempt to run cryptsetup open on a newly created LUKS partition on
  Ubuntu Core 20 causes a kernel crash. This happens in 100% of the
  attempts on the snapd Core 20 installation test, but on an image
  created to reproduce this bug it happens only when certain parameters
  are passed to cryptsetup. Both images are built similarly so the
  reason for this discrepancy is unknown. The kernel was installed from
  pc-kernel_374.snap.

  [Test Case]

  $ dir=$(mktemp -d /tmp/lp1860231.XXXXX)
  $ dmsetup create lp1860231 --notable
  $ mount -t ext4 \
    "/dev/dm-$(dmsetup info -c -o minor --noheadings lp1860231)" "$dir"

  Now check the logs for a backtrace.

  [Regression Potential]

  The currently proposed fix introduces no chance of stability
  regressions. There is a chance of a very small performance regression
  since an additional pointer comparison is performed on each block
  layer request but this is unlikely to be noticeable.

  [Original Report]

  Linux version 5.4.0-11-generic (buildd@lgw01-amd64-021) (gcc version
  9.2.1 20200104 (Ubuntu 9.2.1-22ubuntu2)) #14-Ubuntu SMP Thu Jan 9
  16:14:26 UTC 2020

  Version signature: Ubuntu 5.4.0-11.14-generic 5.4.8

  How to reproduce the crash in 3 "easy" steps:

  1. Build a Core 20 image using the attached model file:
     1.1. Install the ubuntu-image from latest/edge
          $ sudo snap install --channel latest/edge ubuntu-image
     1.2. Build the image
          $ sudo ubuntu-image --image-size=4G ubuntu-core-20-amd64.model

  2. Boot the image in kvm
     2.1. Install ovmf version 0~20190606.20d2e5a1-2ubuntu1 or newer (the
          stock ovmf from bionic may not work)
     2.2. Boot the image
          $ sudo kvm -snapshot -m 2048 -smp 4 \
            -netdev user,id=mynet0,hostfwd=tcp::8022-:22,hostfwd=tcp::8090-:80 \
            -device virtio-net-pci,netdev=mynet0 \
            -drive file=pc.img,if=virtio \
            -bios /usr/share/OVMF/OVMF_CODE.ms.fd
     2.3. In the grub menu, edit the default option to include parameter
          "systemd.debug-shell=1" in the kernel command line
     2.4. Boot the kernel

  3. Crash the kernel
     3.1. When the system boots to the "Press enter to configure"
          message, press ALT-F9 to enter the debug shell.
     3.2. The system should have two partitions in /dev/vda. Create a
          third one with fdisk.
     3.3. Create a LUKS encrypted partition:
          # echo 123|cryptsetup luksFormat -q --type luks2 --key-file - --pbkdf argon2i --iter-time 1 /dev/vda3
          (the system will complain about a missing locking directory,
          just ignore it.)
     3.4. Open the encrypted device:
          # echo 123|cryptsetup open --key-file - /dev/vda name

          The Core 20 images contain the following udev rule which causes
          the new block device to be mounted automatically. This mount is
          what triggers the BUG:
          ACTION=="add", SUBSYSTEM=="block", KERNEL!="loop*", KERNEL!="ram*" \
          RUN+="/usr/bin/unshare -m /usr/bin/snap auto-import --mount=/dev/%k"
     3.5. Read the crash message

  The attached screenshots show these steps being executed.

  A few notes:

  - The backtrace seems very similar to the one reported in bug #1835279, however that problem was possibly caused by a race between partition creation and LUKS formatting. This time it doesn't seem to be the case, delays between commands don't help us here.
  - In the test case above using large values of KDF iter-time may prevent the crash. I successfully opened the device in kernel 5.4.0-9 with --iter-time larger than 100, but 5.4.0-11 seems to require values closer to 1000. Regardless of the --iter-time value used, the crash always happen when running the test in a spread-driven automated environment (same kernel with image built in the same way, some other variable seems to be disturbing the system).
  - All necessary modules are loaded before the LUKS partition creation (i.e. it doesn't seem to be caused by a race between dm-crypt loading and cryptsetup luksFormat for example).

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