Kernel 5.19 is also affected

** Changed in: linux-hwe-5.17 (Ubuntu Kinetic)
       Status: Invalid => Confirmed

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https://bugs.launchpad.net/bugs/1983640

Title:
  refactoring of overlayfs fix to properly support shiftfs

Status in linux package in Ubuntu:
  Fix Released
Status in linux-hwe-5.17 package in Ubuntu:
  Confirmed
Status in linux source package in Jammy:
  Fix Released
Status in linux-hwe-5.17 source package in Jammy:
  Fix Committed
Status in linux source package in Kinetic:
  Fix Released
Status in linux-hwe-5.17 source package in Kinetic:
  Confirmed

Bug description:
  [Impact]

  Starting with 5.13 we've incorrectly dropped the following sauce
  patch:

      UBUNTU: SAUCE: overlayfs: fix incorrect mnt_id of files opened
  from map_files

  This patch is required to use overlayfs on top of shiftfs and without
  this patch we may break containers that rely on shiftfs (using
  zfs/ceph as storage pool w/ shiftfs enabled).

  However, we made this patch dependent on AUFS, starting with Jammy
  we're not enabling AUFS anymore, so this fix becomes a no-op.

  So we need to re-introduce this fix with a bit of refactoring to not
  depend on AUFS.

  [Test case]

  The following script can be used to trigger the issue:

    #!/bin/bash

    cat > test.py << EOF
    import sys

    f = open("/proc/self/maps")

    for l in f.readlines():
      if "python" not in l:
        continue
      print(l)
      s = l.split()
      start, end = s[0].split("-")
      fname = s[-1]
      print(start, end, fname)
      break
    else:
      sys.exit(1)

    test_file1 = open(fname)
    test_file2 = open("/proc/self/map_files/%s-%s" % (start, end))

    fdinfo1 = open("/proc/self/fdinfo/%d" % test_file1.fileno()).read()
    fdinfo2 = open("/proc/self/fdinfo/%d" % test_file2.fileno()).read()

    if fdinfo1 != fdinfo2:
      print("FAIL")
      print(test_file1)
      print(fdinfo1)
      print(test_file2)
      print(fdinfo2)
      sys.exit(1)
    print("PASS")
    EOF
    sudo docker run -it --privileged --rm -v `pwd`:/mnt python python 
/mnt/test.py

  [Fix]

  Import the right pieces from AUFS to properly support the fix and get 
  rid of the AUFS dependency across all our kernels and re-apply the 
  overlayfs fix without the AUFS dependency.

  [Regression potential]

  This patch is touching overlayfs, so we may see potential regressions
  in overlayfs, especially when containers are used.

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