[Bug 1957024] Re: pam-mkhomedir does not honor private home directories

[Timo Aaltonen]

Hello Alex, or anyone else affected,

Accepted pam into jammy-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/pam/1.4.0-11ubuntu2.5
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
jammy to verification-done-jammy. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-jammy. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: pam (Ubuntu Jammy)
       Status: In Progress => Fix Committed

** Tags added: verification-needed verification-needed-jammy

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to pam in Ubuntu.
https://bugs.launchpad.net/bugs/1957024

Title:
  pam-mkhomedir does not honor private home directories

Status in pam package in Ubuntu:
  Fix Released
Status in pam source package in Focal:
  In Progress
Status in pam source package in Jammy:
  Fix Committed
Status in pam source package in Noble:
  Fix Released
Status in pam source package in Oracular:
  Fix Released
Status in pam source package in Plucky:
  Fix Released

Bug description:
  [Impact]

  A common situation is to have a central set of users (e.g. in LDAP)
  and use pam_mkhomedir.so to create the home directory when the user
  first logs in.

  These changes do not cover this situation. The default configuration
  of pam_mkhomedir.so will result in a home directory created with 0755
  permissions.

  To make pam_mkhomedir.so create a home directory by default with
  permissions consistent with the other tools then a umask argument can
  be added to the pam_mkhomedir.so module in the file /usr/share/pam-
  configs/mkhomedir. I believe this would have to be done before
  enabling the module. The file is part of the libpam-modules package.

  [Test plan]

  1. Test with current defaults and confirm the permission is 0755 for home directory.
  # enable pam_mkhomedir.so configuration
  pam-auth-update --enable mkhomedir
  # create a user with adduser that creates the home directory
  adduser --disabled-password --gecos adduser homemadebyadduser
  # create a user with useradd that creates the home directory
  useradd --create-home homemadebyuseradd
  # create a user with useradd that does *not* create the home directory so that pam_mkhomedir.so can create it
  useradd --no-create-home homemadebymkhomedir
  # trigger pam_mkhomedir.so to create the home directory
  su - homemadebymkhomedir -c exit
  # verify the permissions are 0755 for the one created by pam and 0750 for the one by adduser'
  root at ubuntu:~# ls -al /home

  2. Install the package with the fix
  # enable mkhomedir again
  pam-auth-update --enable mkhomedir
  # create a user with useradd that does *not* create the home directory so that pam_mkhomedir.so can create it
  useradd --no-create-home homemadebymkhomedirpatch
  # trigger pam_mkhomedir.so to create the home directory
  su - homemadebymkhomedirpatch -c exit
  # verify that the home dir created by pam has 0750 as well

  [ Where problems could occur ]

  This could result in inconsistent permissions between existing home directories created by pam (before the fix) and the ones created with this fix. While there's no reason to believe it could result in any actual issues, this can
  be mitigated by changing the existing home directories to have 0750 for consistency.

  Anyone in the 'others' group will lose access to the home directories of the
  rest of the users whose $HOME was created by pam. That behaviour should be
  treated as unexpected as that's how $HOME adduser will behave. In general,
  one's not expected to have access to $HOME of others.

  In the absolute pathological cases, where it's desired to give to $HOME to
  everyone, the permissions can be adjusted manually and the umask can be changed
  in the conf file on those systems. But this should be treated as 'workaround' and non-standard behaviour.

  [other info]

  This has been at https://discourse.ubuntu.com/t/private-home-
  directories-for-ubuntu-21-04-onwards/19533/13:

  And agreed that (1) having $HOME consistent across tools is the right
  behaviour and (2) 0750 is the desired permission for $HOME.

  This has been merged into Plucky already:
  https://git.launchpad.net/ubuntu/+source/pam/commit/?id=c576b5c19abb383ce53dfc10a986d7cf164eaeaf

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/pam/+bug/1957024/+subscriptions