Bug 2115094

Description of problem:

This issue is related to https://bugzilla.redhat.com/show_bug.cgi?id=1891847

On my system, I have pointed the /etc/resolv.conf symlink to ../run/systemd/resolve/resolv.conf. I do not have DNSStubListener disabled in resolved.conf.  Updating the systemd package causes that symlink to be overwritten with a link to ../run/systemd/resolve/stub-resolv.conf

Opening this with "low" severity because DNS is not broken, but the resolution process has changed unexpectedly.

Version-Release number of selected component (if applicable): systemd-251.3-2.fc37.x86_64 (and earlier)


How reproducible: 100%


Steps to Reproduce:
1. Start with an up-to-date Fedora 36 system
2. Update the /etc/resolv.conf symlink to point to systemd-resolved's resolv.conf: sudo ln -sf ../run/systemd/resolve/resolv.conf /etc/resolv.conf
3. Update to systemd from rawhide: sudo dnf update systemd --releasever=rawhide
4. Inspect the /etc/resolv.conf symlink

Actual results:

The /etc/resolv.conf symlink has been updated to point to ../run/systemd/resolve/stub-resolv.conf

Expected results:

The /etc/resolv.conf symlink was preserved such that it still points to ../run/systemd/resolve/resolv.conf

Additional info:

The %posttrans resolved section in the spec file contains the following:

# Also don't create the symlink to the stub when the stub is disabled (#1891847 again).

if systemctl -q is-enabled systemd-resolved.service &>/dev/null &&
   ! systemd-analyze cat-config systemd/resolved.conf 2>/dev/null |
        grep -iqE '^DNSStubListener\s*=\s*(no?|false|0|off)\s*$'; then

  if ! test -e /etc/resolv.conf && ! test -L /etc/resolv.conf; then
    ln -sv ../run/systemd/resolve/stub-resolv.conf /etc/resolv.conf || :
  elif test -d /run/systemd/system/ &&
     ! mountpoint /etc/resolv.conf &>/dev/null; then
    ln -fsv ../run/systemd/resolve/stub-resolv.conf /etc/resolv.conf || :
  fi
fi


This code checks to see if DNSStubListener is disabled, and avoids replacing /etc/resolv.conf if it is. However, the situation in which /etc/resolv.conf points to /run/systemd/resolve/resolv.conf even when DNSStubListener is enabled is valid and is not detected.  One possible solution to this might be to add an additional condition to the outer `if` block:

   [ $(readlink -f /etc/resolv.conf) != /run/systemd/resolve/resolv.conf ]