[Bug 2137169] Re: Propagation of sgid bit lost

[Julian Andres Klode]

This was fixed in https://github.com/uutils/coreutils/pull/10036

** Bug watch added: github.com/uutils/coreutils/issues #10022
   https://github.com/uutils/coreutils/issues/10022

** Also affects: rust-coreutils via
   https://github.com/uutils/coreutils/issues/10022
   Importance: Unknown
       Status: Unknown

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Title:
  Propagation of sgid bit lost

Status in rust-coreutils:
  Unknown
Status in rust-coreutils package in Ubuntu:
  Fix Committed

Bug description:
  Very strange problem I did not see under 22.04 and 25.04. Just to
  verify I've just setup a notebook with fresh Kubuntu 25.04 (problem
  does not occur) and Kubuntu 25.10 (problem does occur):

  [Kubuntu 25.10 freshly installed from scratch, just apt update , apt
  upgrade, nothing else changed, cdrom is just a randomly selected group
  I'm member of, doesn't matter, which one, just needs to be different
  from the default group and you have to be member of; it's a kubuntu
  standard installation with ext4 on an encrypted device]

  hadmut at test10:~$ id
  uid=1000(hadmut) gid=1000(hadmut) groups=1000(hadmut),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),115(lpadmin),986(sambashare)
  hadmut at test10:~$ mkdir a
  hadmut at test10:~$ chgrp cdrom a
  hadmut at test10:~$ chmod 2770 a
  hadmut at test10:~$ mkdir a/b
  hadmut at test10:~$ mkdir a/b/c
  hadmut at test10:~$ find a -ls
    9438665      4 drwxrws---   3 hadmut   cdrom        4096 Dez 27 17:08 a
    9438668      4 drwxrwxr-x   3 hadmut   cdrom        4096 Dez 27 17:08 a/b
    9438669      4 drwxrwxr-x   2 hadmut   hadmut       4096 Dez 27 17:08 a/b/c

  Problem:               ^                 ^^^^^^

  
  Usually, the g+s flag on directories do propagate to newly created sub directories, and all three directories a b c should have g+s and group cdrom. And that's what it does on Ubunbu 24.04 server and Kubuntu 25.04 and any other distribution I have tested, and that's what I had learned about Unix over 30 years ago. 

  But here the g+s bit is not propagated here, it's lost on b, although
  b is still group cdrom, and therefore, consequently, on c both are
  lost, the g+s and the group cdrom.

  
  This can be a security problem in rare cases, if the default group is not supposed to have read access, or if it forces admins to use wider permissions.  


  
  IMPORTANT QUESTION: Has the Ubuntu Kernels file system driver been tampered with?

  
  Please check this before making this bug publicly readable.

  ProblemType: Bug
  DistroRelease: Ubuntu 25.10
  Package: linux-image-6.17.0-8-generic 6.17.0-8.8
  ProcVersionSignature: Ubuntu 6.17.0-8.8-generic 6.17.2
  Uname: Linux 6.17.0-8-generic x86_64
  ApportVersion: 2.33.1-0ubuntu3
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  hadmut     1565 F.... pipewire
                        hadmut     1570 F.... wireplumber
   /dev/snd/pcmC0D0p:   hadmut     1565 F...m pipewire
   /dev/snd/seq:        hadmut     1565 F.... pipewire
  CasperMD5CheckResult: unknown
  CurrentDesktop: KDE
  Date: Sat Dec 27 17:04:32 2025
  InstallationDate: Installed on 2025-12-27 (0 days ago)
  InstallationMedia: Kubuntu 25.10 "Questing Quokka" - Release amd64 (20251007)
  MachineType: FUJITSU LIFEBOOK U727
  ProcFB: 0 i915drmfb
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-6.17.0-8-generic root=UUID=7c3f1902-a696-4fab-bdbf-8a9304ea1153 ro quiet rd.luks.uuid=4d043596-4dc2-471b-a179-fb78e3248b5b splash vt.handoff=7
  PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon.
  RelatedPackageVersions:
   firmware-sof   N/A
   linux-firmware 20250901.git993ff19b-0ubuntu1.4
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 01/10/2023
  dmi.bios.release: 1.21
  dmi.bios.vendor: FUJITSU // Insyde Software Corp.
  dmi.bios.version: Version 1.21
  dmi.board.name: FJNB2B1
  dmi.board.vendor: FUJITSU
  dmi.board.version: B4
  dmi.chassis.type: 10
  dmi.chassis.vendor: FUJITSU
  dmi.chassis.version: LIFEBOOK U727
  dmi.modalias: dmi:bvnFUJITSU//InsydeSoftwareCorp.:bvrVersion1.21:bd01/10/2023:br1.21:svnFUJITSU:pnLIFEBOOKU727:pvr10601736746:rvnFUJITSU:rnFJNB2B1:rvrB4:cvnFUJITSU:ct10:cvrLIFEBOOKU727:skuSK00:
  dmi.product.family: LIFEBOOK-FTS
  dmi.product.name: LIFEBOOK U727
  dmi.product.sku: SK00
  dmi.product.version: 10601736746
  dmi.sys.vendor: FUJITSU

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