[Bug 1849730] [NEW] [live-usb-persistent] second partition as casper-rw issue

[Andrey de Oliveira]

Public bug reported:

Hi!

I identified a problem for creating persistent live usb sticks when
using a second partition for 'casper-rw'.

Environment:
On the usb stick I created two partitions:
- The first partition (/dev/sda1) is vfat which is used for the live-filesystem (filesystem.squashfs).
- The second partition (/dev/sda2) is ext4 and labeled 'casper-rw' which is used for persistence.

cat /proc/cmdline
BOOT_IMAGE=(hd0,msdos1)/casper/vmlinuz file=/preseed/lubuntu.seed boot=casper quiet splash persistent ignore_uuid ---

Error in initramfs (casper.log) while boot:
mount: mounting /cow on /root failed: Invalid argument
overlay mount failed

Tested versions (Lubuntu): 
Lubuntu 18.04 (LTS) - Package casper/now 1.394 amd64
Lubuntu 19.10 - Pacakge casper/eoan 1.427 amd64

Bug:
I found a bug in find_cow_device() function of casper-helpers script from initram that is responsible for this.

When the setup_unionfs() function of the casper script invokes the
find_cow_device() function, the live filesystem  partition that was
mounted in the mountroot() function is unmounted every time the function
tries to search for a persistent file, making it impossible to boot.

When a casper-rw file exists and is used, the problem just doesn't
happen because the partition is mounted and busy, so you can't unmount
it.

To correct the problem, I have included a check to not unmount the
partition if it is the live-filesystem partition. In that case, just
return it to read-only.

My fix for casper-helpers script in  Lubuntu 19.10 'casper/eoan 1.427
amd64' package:

/usr/share/initramfs-tools/scripts# diff -u casper-helpers casper-helpers.fix
--- casper-helpers      2019-10-14 12:29:05.000000000 -0300
+++ casper-helpers.fix  2019-10-24 17:09:42.635313048 -0300
@@ -247,8 +247,10 @@
                 if [ -e "${cow_backing}/${pers_fpath}" ]; then
                     echo $(setup_loop "${cow_backing}/${pers_fpath}" "loop" "/sys/block/loop*")
                     return 0
-                else
+                elif [ ${cow_backing} != ${livefs_root} ]; then
                     umount ${cow_backing}
+                else
+                        try_mount "${devname}" "${cow_backing}" "ro"
                 fi
             fi
         done
---CUT HERE---

My fix for casper-helpers script in  Lubuntu 18.04 (LTS) 'casper/now
1.394 amd64' package:

/usr/share/initramfs-tools/scripts# diff -u casper-helpers casper-helpers.fix
--- casper-helpers       2019-10-24 11:29:58.735085568 -0300
+++ casper-helpers.fix 2019-10-24 16:53:19.375302075 -0300
@@ -223,8 +223,10 @@
                 if [ -e "${cow_backing_mp}/${pers_fpath}" ]; then
                     echo $(setup_loop "${cow_backing_mp}/${pers_fpath}" "loop" "/sys/block/loop*")
                     return 0
-                else
+                elif [ ${cow_backing_mp} != ${livefs_root} ]; then
                     umount ${cow_backing_mp}
+               else
+                       try_mount "${devname}" "${cow_backing}" "ro"
                 fi
             fi
         done
---CUT HERE---

** Affects: casper (Ubuntu)
     Importance: Undecided
         Status: New

-- 
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https://bugs.launchpad.net/bugs/1849730

Title:
  [live-usb-persistent] second partition as casper-rw issue

Status in casper package in Ubuntu:
  New

Bug description:
  Hi!

  I identified a problem for creating persistent live usb sticks when
  using a second partition for 'casper-rw'.

  Environment:
  On the usb stick I created two partitions:
  - The first partition (/dev/sda1) is vfat which is used for the live-filesystem (filesystem.squashfs).
  - The second partition (/dev/sda2) is ext4 and labeled 'casper-rw' which is used for persistence.

  cat /proc/cmdline
  BOOT_IMAGE=(hd0,msdos1)/casper/vmlinuz file=/preseed/lubuntu.seed boot=casper quiet splash persistent ignore_uuid ---

  Error in initramfs (casper.log) while boot:
  mount: mounting /cow on /root failed: Invalid argument
  overlay mount failed

  Tested versions (Lubuntu): 
  Lubuntu 18.04 (LTS) - Package casper/now 1.394 amd64
  Lubuntu 19.10 - Pacakge casper/eoan 1.427 amd64

  Bug:
  I found a bug in find_cow_device() function of casper-helpers script from initram that is responsible for this.

  When the setup_unionfs() function of the casper script invokes the
  find_cow_device() function, the live filesystem  partition that was
  mounted in the mountroot() function is unmounted every time the
  function tries to search for a persistent file, making it impossible
  to boot.

  When a casper-rw file exists and is used, the problem just doesn't
  happen because the partition is mounted and busy, so you can't unmount
  it.

  To correct the problem, I have included a check to not unmount the
  partition if it is the live-filesystem partition. In that case, just
  return it to read-only.

  My fix for casper-helpers script in  Lubuntu 19.10 'casper/eoan 1.427
  amd64' package:

  /usr/share/initramfs-tools/scripts# diff -u casper-helpers casper-helpers.fix
  --- casper-helpers      2019-10-14 12:29:05.000000000 -0300
  +++ casper-helpers.fix  2019-10-24 17:09:42.635313048 -0300
  @@ -247,8 +247,10 @@
                   if [ -e "${cow_backing}/${pers_fpath}" ]; then
                       echo $(setup_loop "${cow_backing}/${pers_fpath}" "loop" "/sys/block/loop*")
                       return 0
  -                else
  +                elif [ ${cow_backing} != ${livefs_root} ]; then
                       umount ${cow_backing}
  +                else
  +                        try_mount "${devname}" "${cow_backing}" "ro"
                   fi
               fi
           done
  ---CUT HERE---

  My fix for casper-helpers script in  Lubuntu 18.04 (LTS) 'casper/now
  1.394 amd64' package:

  /usr/share/initramfs-tools/scripts# diff -u casper-helpers casper-helpers.fix
  --- casper-helpers       2019-10-24 11:29:58.735085568 -0300
  +++ casper-helpers.fix 2019-10-24 16:53:19.375302075 -0300
  @@ -223,8 +223,10 @@
                   if [ -e "${cow_backing_mp}/${pers_fpath}" ]; then
                       echo $(setup_loop "${cow_backing_mp}/${pers_fpath}" "loop" "/sys/block/loop*")
                       return 0
  -                else
  +                elif [ ${cow_backing_mp} != ${livefs_root} ]; then
                       umount ${cow_backing_mp}
  +               else
  +                       try_mount "${devname}" "${cow_backing}" "ro"
                   fi
               fi
           done
  ---CUT HERE---

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