deploy: Ignore sockets, fifos in /etc during merge

https://bugzilla.redhat.com/show_bug.cgi?id=1945274 is an issue where a privileged
kubernetes daemonset is writing a socket into `/etc`.  This makes ostree upgrades barf.

Now, they should clearly move it to `/run`.  However, one option is for us to
just ignore it instead of erroring out.  Some brief investigation shows that
e.g. `git add somesocket` is a silent no-op, which is an argument in favor of ignoring it.

Closes: #2446

src/libostree/ostree-sysroot-deploy.c

@@ -488,9 +488,7 @@ copy_modified_config_file (int                 orig_etc_fd,
     }
   else
     {
-      return glnx_throw (error,
-                         "Unsupported non-regular/non-symlink file in /etc '%s'",
-                         path);
+      ot_journal_print (LOG_INFO, "Ignoring non-regular/non-symlink file found during /etc merge: %s", path);
     }
 
   return TRUE;

tests/kolainst/destructive/staged-deploy.sh

@@ -12,6 +12,23 @@ case "${AUTOPKGTEST_REBOOT_MARK:-}" in
   test -f /run/systemd/generator/multi-user.target.wants/ostree-finalize-staged.path
   test -f /run/systemd/generator/local-fs.target.requires/ostree-remount.service
 
+  cat >/etc/systemd/system/sock-to-ignore.socket << 'EOF'
+[Socket]
+ListenStream=/etc/sock-to-ignore
+EOF
+  cat >/etc/systemd/system/sock-to-ignore.service << 'EOF'
+[Service]
+ExecStart=/bin/cat
+EOF
+  # policy denies systemd listening on a socket in /etc (arguably correctly)
+  setenforce 0
+  systemctl daemon-reload
+  systemctl start --now sock-to-ignore.socket
+  setenforce 1
+
+  test -S /etc/sock-to-ignore
+  mkfifo /etc/fifo-to-ignore
+
   # Initial cleanup to handle the cosa fast-build case
     ## TODO remove workaround for https://github.com/coreos/rpm-ostree/pull/2021
     mkdir -p /var/lib/rpm-ostree/history
@@ -54,6 +71,9 @@ case "${AUTOPKGTEST_REBOOT_MARK:-}" in
     # Assert that the previous boot had a journal entry for it
     journalctl -b "-1" -u ostree-finalize-staged.service > svc.txt
     assert_file_has_content svc.txt 'Bootloader updated; bootconfig swap: yes;.*deployment count change: 1'
+    # Also validate ignoring socket and fifo
+    assert_file_has_content svc.txt 'Ignoring.*during /etc merge:.*sock-to-ignore'
+    assert_file_has_content svc.txt 'Ignoring.*during /etc merge:.*fifo-to-ignore'
     rm -f svc.txt
     # And there should not be a staged deployment
     test '!' -f /run/ostree/staged-deployment

tests/test-admin-deploy-etcmerge-cornercases.sh

@@ -51,6 +51,9 @@ chmod 700 ${etc}/a/long/dir/forking
 # Symlink to nonexistent path, to ensure we aren't walking symlinks
 ln -s no-such-file ${etc}/a/link-to-no-such-file
 
+# fifo which should be ignored
+mkfifo "${etc}/fifo-to-ignore"
+
 # Remove a directory
 rm ${etc}/testdirectory -rf
 
@@ -66,6 +69,10 @@ newetc=${newroot}/etc
 assert_file_has_content ${newroot}/usr/etc/NetworkManager/nm.conf "a default daemon file"
 assert_file_has_content ${newetc}/NetworkManager/nm.conf "a modified config file"
 
+if test -e "${newetc}"/fifo-to-ignore; then
+  fatal "Should not have copied fifo!"
+fi
+
 assert_file_has_mode() {
   stat -c '%a' $1 > mode.txt
   if ! grep -q -e "$2" mode.txt; then