Public bug reported:
Hello,
in Focal the behaviour has changed when a program running as root tries
to modify a file which belongs to a user/group other than root in a
directory with sticky bit set.
I'm not sure if this is a bug or the behaviour is intentional (for
certain security reasons).
Steps to reproduce:
- Boot current Focal daily iso
- Open terminal
- Create a directory with sticky bit set (chmod o+t; or use an existing
directory with sticky bit, e.g. /var/crash )
- Create an empty file with user:group set to anything different that root
(e.g. ubuntu:ubuntu, ubuntu:whoospie, ...)
- Open the file with nano running as root (sudo nano testfile.txt), write
something in it, and try to save it. This won't work and gives a "permission
denied" error message.
This behaviour is different than in previous Ubuntu versions. In Eoan it
is possible to modify the file as root in the scenario described above.
I discovered this because after changing my main installation to Eoan I
noticed that I got weird error messages from rsync when backing up my
root subvolume. In my backup script rsync runs as root, and can't update
backed up contents of /var/crash or /var/spool/cups/tmp anymore because
it isn't allowed to modify the respective files anymore.
For me personally this is a regression compared to previous Ubuntu
versions where I never saw such errors during backup.
Whether PAM is the appropriate package to report this bug against I'm
not sure, so please feel free to assign it to the correct package.
If this is intentional, does anybody have a clue how to work around this
for use cases like backup with rsync?
Kind regards,
Jan
ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: libpam-runtime 1.3.1-5ubuntu4
ProcVersionSignature: Ubuntu 5.4.0-24.28-generic 5.4.30
Uname: Linux 5.4.0-24-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: KDE
Date: Mon Apr 20 12:11:32 2020
InstallationDate: Installed on 2020-04-08 (11 days ago)
InstallationMedia: Kubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200408)
PackageArchitecture: all
SourcePackage: pam
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: pam (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug focal
** Description changed:
Hello,
in Focal the behaviour has changed when a program running as root tries
to modify a file which belongs to a user/group other than root in a
directory with sticky bit set.
I'm not sure if this is a bug or the behaviour is intentional (for
certain security reasons).
Steps to reproduce:
- Boot current Focal daily iso
- Open terminal
- Create a directory with sticky bit set (chmod o+t; or use an existing
directory with sticky bit, e.g. /var/crash )
- Create an empty file with user:group set to anything different that root
(e.g. ubuntu:ubuntu, ubuntu:whoospie, ...)
- Open the file with nano running as root (sudo nano testfile.txt), write
something in it, and try to save it. This won't work and gives a "permission
denied" error message.
This behaviour is different than in previous Ubuntu versions. In Eoan it
is possible to modify the file as root in the scenario described above.
I discovered this because after changing my main installation to Eoan I
noticed that I got weird error messages from rsync when backing up my
root subvolume. In my backup script rsync runs as root, and can't update
backed up contents of /var/crash or /var/spool/cups/tmp anymore because
it isn't allowed to modify the respective files anymore.
For me personally this is a regression compared to previous Ubuntu
versions where I never saw such errors during backup.
Whether PAM is the appropriate package to report this bug against I'm
not sure, so please feel free to assign it to the correct package.
- If this is intentional, does anybode have a clue how to work around this
+ If this is intentional, does anybody have a clue how to work around this
for use cases like backup with rsync?
Kind regards,
Jan
ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: libpam-runtime 1.3.1-5ubuntu4
ProcVersionSignature: Ubuntu 5.4.0-24.28-generic 5.4.30
Uname: Linux 5.4.0-24-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: KDE
Date: Mon Apr 20 12:11:32 2020
InstallationDate: Installed on 2020-04-08 (11 days ago)
InstallationMedia: Kubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200408)
PackageArchitecture: all
SourcePackage: pam
UpgradeStatus: No upgrade log present (probably fresh install)
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https://bugs.launchpad.net/bugs/1873785
Title:
Root can't modify files of other users in directories with sticky bit
anymore
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