Bug 2111251

+++ This bug was initially created as a clone of Bug #2110787 +++

Description of problem:

Upgrading fapolicyd along with other packages (e.g. system) leave yum in a
hung state, writing to a fifo on which no other process reads.

Version-Release number of selected component (if applicable):

fapolicyd-1.1-103.el9_0
rpm-plugin-fapolicyd-4.16.1.3-12.el9_0

How reproducible:

Always

Steps to Reproduce:

1. Install of RHEL 8.4 (server with GUI). Register the system and attach the
   required entitlement.

2. Lock the release version

   subscription-manager release --set=8.4

2. Enable fapolicyd

   # systemctl enable --now fapolicyd

3. Update the packages but leave systemd one step behind (for step 5)

   # yum upgrade -y -x fapolicyd\* -x systemd\*
   # yum upgrade -y systemd-239-45.el8_4.10
   # yum upgrade -y fapolicyd-1.0.2-6.el8_4.1
   # systemctl reboot

4. Download the attached test rpms. These are scratch builds of fapolicyd with
   this change to force an upgrade:

   diff --git a/fapolicyd.spec b/fapolicyd.spec
   index e7d2c5c..03334a0 100644
   --- a/fapolicyd.spec
   +++ b/fapolicyd.spec
   @@ -6,7 +6,7 @@
    Summary: Application Whitelisting Daemon
    Name: fapolicyd
    Version: 1.0.2
   -Release: 6%{?dist}.2_case03267178
   +Release: 6%{?dist}.1
    License: GPLv3+
    URL: http://people.redhat.com/sgrubb/fapolicyd
    Source0: https://people.redhat.com/sgrubb/fapolicyd/%{name}-%{version}.tar.gz
   @@ -57,13 +57,6 @@ to decide file access rights. Applications that are known via a reputation
    source are allowed access while unknown applications are not. The daemon
    makes use of the kernel's fanotify interface to determine file access rights.
    
   -This RPM has been provided by Red Hat for testing purposes only and is
   -NOT supported for any other use. This RPM may contain changes that are
   -necessary for debugging but that are not appropriate for other uses,
   -or that are not compatible with third-party hardware or software. This
   -RPM should NOT be deployed for purposes other than testing and
   -debugging.
   -
    %package        selinux
    Summary:        Fapolicyd selinux
    Group:          Applications/System

5. Upgrade systemd and fapolicyd in a single yum execution

   # yum upgrade systemd-239-45.el8_4.11 \
   ./fapolicyd-1.0.2-6.el8_4.2_case03267178.x86_64.rpm \
   ./fapolicyd-selinux-1.0.2-6.el8_4.2_case03267178.noarch.rpm

Actual results:

Yum gets hung.

Expected results:

Successful upgrade.

Additional info:

Yum gets hung writing on the fifo used by the fapolicyd rpm plugin to communicate with fapolicyd, as
can be seen using strace:

# pid=$(pidof -x yum)
# strace -fttTvyy -s 4096 -p $pid
strace: Process 6074 attached
18:01:56.359949 write(24</run/fapolicyd/fapolicyd.fifo (deleted)>, "/usr/lib/systemd/system/remote-cryptsetup.target 549 86d9439857b2d5e306805a4a9d83e35cf9cde9e31c5305557c321c3254cc8909\n", 118

# lsof -p $pid | fgrep /run/fapolicyd/fapolicyd.fifo
yum     6074 root   24u  FIFO               0,24       0t0    25332 /run/fapolicyd/fapolicyd.fifo (deleted)

The FIFO is deleted because fapolicyd has been restarted. The new fapolicyd daemon uses a different
fifo:

# ls -l /run/fapolicyd/fapolicyd.fifo
prw-rw----. 1 root fapolicyd 0 Jul 25 17:59 /run/fapolicyd/fapolicyd.fifo

# lsof -p $(pidof fapolicyd) | fgrep /run/fapolicyd/fapolicyd.fifo
fapolicyd 6120 fapolicyd    3u     FIFO               0,24      0t0    46280 /run/fapolicyd/fapolicyd.fifo

So the yum process becomes blocked, writing on a FIFO on which no other process reads.

This problem should have been fixed in Bug 1896875 but is still present.