[Bug 1902236] Re: Duplicated root and nobody returned by getent on Focal

Simon Déziel 1902236 at bugs.launchpad.net
Mon Mar 8 13:23:11 UTC 2021 

Verification procedure on Focal:

$ lxc launch focal lp1902236-f
Creating lp1902236-f
Starting lp1902236-f
$ lxc exec lp1902236-f bash
root at lp1902236-f:~# getent passwd | grep root
root:x:0:0:root:/root:/bin/bash
root:x:0:0:root:/root:/bin/sh
root at lp1902236-f:~# getent passwd | grep nobody
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/:/usr/sbin/nologin

# Enable proposed
root at lp1902236-f:~# vim /etc/apt/sources.list

root at lp1902236-f:~# apt update && apt-get dist-upgrade
Calculating upgrade... Done
The following packages will be upgraded:
   libnss-systemd (245.4-4ubuntu3.4 => 245.4-4ubuntu3.5)
   libpam-systemd (245.4-4ubuntu3.4 => 245.4-4ubuntu3.5)
   libsystemd0 (245.4-4ubuntu3.4 => 245.4-4ubuntu3.5)
   libudev1 (245.4-4ubuntu3.4 => 245.4-4ubuntu3.5)
   systemd (245.4-4ubuntu3.4 => 245.4-4ubuntu3.5)
   systemd-sysv (245.4-4ubuntu3.4 => 245.4-4ubuntu3.5)
   systemd-timesyncd (245.4-4ubuntu3.4 => 245.4-4ubuntu3.5)
   udev (245.4-4ubuntu3.4 => 245.4-4ubuntu3.5)
8 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 5845 kB of archives.
After this operation, 15.4 kB of additional disk space will be used.
Do you want to continue? [Y/n] 
Get:1 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 libnss-systemd amd64 245.4-4ubuntu3.5 [95.8 kB]
Get:2 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 udev amd64 245.4-4ubuntu3.5 [1366 kB]
Get:3 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 libudev1 amd64 245.4-4ubuntu3.5 [81.2 kB]
Get:4 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 systemd-sysv amd64 245.4-4ubuntu3.5 [10.3 kB]
Get:5 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 systemd-timesyncd amd64 245.4-4ubuntu3.5 [28.1 kB]
Get:6 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 libpam-systemd amd64 245.4-4ubuntu3.5 [186 kB]
Get:7 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 systemd amd64 245.4-4ubuntu3.5 [3805 kB]
Get:8 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 libsystemd0 amd64 245.4-4ubuntu3.5 [274 kB]
Fetched 5845 kB in 2s (2391 kB/s)    
...
Setting up libnss-systemd:amd64 (245.4-4ubuntu3.5) ...
Setting up libpam-systemd:amd64 (245.4-4ubuntu3.5) ...
Processing triggers for libc-bin (2.31-0ubuntu9.2) ...
Processing triggers for dbus (1.12.16-2ubuntu2.1) ...

root at lp1902236-f:~# getent passwd | grep root
root:x:0:0:root:/root:/bin/bash
root at lp1902236-f:~# getent passwd | grep nobody
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin

** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done verification-done-focal

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https://bugs.launchpad.net/bugs/1902236

Title:
  Duplicated root and nobody returned by getent on Focal

Status in systemd:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Focal:
  Fix Committed

Bug description:
  [impact]

  getent password or getent group returns duplicate, false/synthesized,
  entries for root and nobody

  [test case]

  root at lp1902236-f:~# getent passwd | grep root
  root:x:0:0:root:/root:/bin/bash
  root:x:0:0:root:/root:/bin/sh
  root at lp1902236-f:~# getent group | grep root
  root:x:0:
  root:x:0:

  root at lp1902236-f:~# getent passwd | grep nobody
  nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
  nobody:x:65534:65534:nobody:/:/usr/sbin/nologin
  root at lp1902236-f:~# getent group | grep nogroup
  nogroup:x:65534:
  nogroup:x:65534:

  [regression potential]

  any regression would likely result in incorrect results to calls to
  getent or other programs using libnss-systemd

  [scope]

  this is needed only for f

  this was fixed upstream by commit
  9494da41c271bb9519d3484b6016526a72cc6be5 which was included first in
  v246, so this is fixed in g and later already.

  b and earlier doesn't show the duplication.

  [original description]

  * Summary

  systemd's NSS integration causes getent passwd/group to return
  duplicated entries for root/root and nobody/nogroup. The root account
  also gets a different shell (/bin/sh instead of /bin/bash).

  * Steps to reproduce:

  1) create a container
  $ lxc launch images:ubuntu/focal test-nobody
  2) check the root and nobody accounts
  $ lxc exec test-nobody -- getent passwd | grep -E '^(root|nobody):'
  3) check the root and nogroup groups
  $ lxc exec test-nobody -- getent group | grep -E '^(root|nogroup):'

  2 and 3 should report a single entry for each account/group but they
  return dups like this:

  root:x:0:0:root:/root:/bin/bash
  nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
  root:x:0:0:root:/root:/bin/sh
  nobody:x:65534:65534:nobody:/:/usr/sbin/nologin

  * Description

  The problem seems to come from the NSS integration:

  $ lxc exec test-nobody -- grep -wF systemd /etc/nsswitch.conf
  passwd:         files systemd
  group:          files systemd

  as the /etc/passwd and /etc/group file contain no dups:

  $ lxc exec test-nobody -- grep ^nobody: /etc/passwd
  nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
  $ lxc exec test-nobody -- grep ^nogroup: /etc/group
  nogroup:x:65534:

  Removing systemd from /etc/nsswitch.conf indeed removes the dup.

  An alternative way of seeing what systemd adds on top of the flat
  files:

  $ lxc exec test-nobody -- bash -c 'diff -u /etc/passwd <(getent passwd)'
  --- /etc/passwd	2020-10-30 13:07:52.219261001 +0000
  +++ /dev/fd/63	2020-10-30 13:29:38.396928732 +0000
  @@ -24,3 +24,5 @@
   _apt:x:105:65534::/nonexistent:/usr/sbin/nologin
   ubuntu:x:1000:1000::/home/ubuntu:/bin/bash
   systemd-coredump:x:999:999:systemd Core Dumper:/:/usr/sbin/nologin
  +root:x:0:0:root:/root:/bin/sh
  +nobody:x:65534:65534:nobody:/:/usr/sbin/nologin

  $ lxc exec test-nobody -- bash -c 'diff -u /etc/group <(getent group)'
  --- /etc/group	2020-10-30 13:07:52.211261089 +0000
  +++ /dev/fd/63	2020-10-30 13:29:45.892846747 +0000
  @@ -50,3 +50,5 @@
   ubuntu:x:1000:
   ssh:x:111:
   systemd-coredump:x:999:
  +root:x:0:
  +nogroup:x:65534:

  * Additional information

  This bug seems to occur on Focal alone as Bionic and Groovy are not
  affected.

  $ lsb_release -rd
  Description:	Ubuntu 20.04.1 LTS
  Release:	20.04

  $ apt-cache policy base-passwd systemd
  base-passwd:
    Installed: 3.5.47
    Candidate: 3.5.47
    Version table:
   *** 3.5.47 500
          500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages
          100 /var/lib/dpkg/status
  systemd:
    Installed: 245.4-4ubuntu3.2
    Candidate: 245.4-4ubuntu3.2
    Version table:
   *** 245.4-4ubuntu3.2 500
          500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       245.4-4ubuntu3 500
          500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

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