package bacula-sd 9.4.2-2ubuntu3 failed to install/upgrade: installed bacula-sd package post-installation script subprocess returned error exit status 2

sudo apt autoremove
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
  libffi6 libsbc1 linux-modules-4.15.0-1050-oem
0 upgraded, 0 newly installed, 3 to remove and 0 not upgraded.
2 not fully installed or removed.
After this operation, 237 MB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 191721 files and directories currently installed.)
Removing libffi6:amd64 (3.2.1-9) ...
Removing libsbc1:amd64 (1.4-1) ...
Removing linux-modules-4.15.0-1050-oem (4.15.0-1050.57) ...
Setting up bacula-sd (9.4.2-2ubuntu3) ...
/var/lib/dpkg/info/bacula-sd.postinst: 20: cannot create /tmp/bacula-sd.conf.ucf
tmp-mzPPNjKGZk: Permission denied
dpkg: error processing package bacula-sd (--configure):
 installed bacula-sd package post-installation script subprocess returned error
exit status 2
dpkg: dependency problems prevent configuration of bacula-bscan:
 bacula-bscan depends on bacula-sd (= 9.4.2-2ubuntu3); however:
  Package bacula-sd is not configured yet.

dpkg: error processing package bacula-bscan (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup erro
r from a previous failure.
                          Processing triggers for libc-bin (2.30-0ubuntu3) ...
Errors were encountered while processing:
 bacula-sd
 bacula-bscan
E: Sub-process /usr/bin/dpkg returned an error code (1)

Thanks for taking the time to report this bug and helping to make Ubuntu better. We appreciate the difficulties you are facing, but this appears to be a "regular" (non-security) bug. I have unmarked it as a security issue since this bug does not show evidence of allowing attackers to cross privilege boundaries nor directly cause loss of data/privacy. Please feel free to report any other bugs you may find.

Status changed to 'Confirmed' because the bug affects multiple users.

I tried to install bacula/9.4.2-2ubuntu4 in a clean Ubuntu Focal LXD container and got this exactly failure. As you can see this is the part of the log relevant for this issue:

Setting up bacula-sd (9.4.2-2ubuntu3) ...
/var/lib/dpkg/info/bacula-sd.postinst: 20: cannot create /tmp/bacula-sd.conf.ucftmp-FdWyL4UBja: Permission denied
dpkg: error processing package bacula-sd (--configure):
 installed bacula-sd package post-installation script subprocess returned error exit status 2

The bacula-sd postinst script creates a temporary file and tries to use it to handle the conffile template, replacing the passwords and so on. The problem is that before adding content to this temporary file it changes its permission and owner, and after that even root user is not able to modify it (sed command in line 20).

If you place lines 17 and 18 (chmod and chown) of the bacula-sd postinst script after the sed command (line 20), and run 'apt install -f' the installation is finished successfully.

I just submitted a merge proposal to fix this bug here:

https://code.launchpad.net/~lucaskanashiro/ubuntu/+source/bacula/+git/bacula/+merge/382147

This bug was fixed in the package bacula - 9.4.2-2ubuntu5

---------------
bacula (9.4.2-2ubuntu5) focal; urgency=medium

  * d/bacula-sd.postinst: let root user modify $TMP_CONFIG file
    (LP: #1861514). Currently, the root user tries to modify the $TMP_CONFIG
    file and it gets a permission denied error because the persmission and owner
    is changed before any modification in this file is applied. Letting root
    user modify $TMP_CONFIG first and then set the permissions fix this
    installation issue.

 -- Lucas Kanashiro <email address hidden> Mon, 13 Apr 2020 19:05:09 -0300