TEST-22: add test for unprivileged dirs in root prefixes

This verifies the fix for the issue described in:
https://github.com/systemd/systemd/pull/11820

diff --git a/test/TEST-22-TMPFILES/test-08.sh b/test/TEST-22-TMPFILES/test-08.sh
new file mode 100755 (executable)
index 0000000..e7bf044
--- /dev/null
+++ b/test/TEST-22-TMPFILES/test-08.sh
@@ -0,0 +1,32 @@
+#! /bin/bash
+#
+# Verify tmpfiles can run in a root directory under a path prefix that contains
+# directories owned by unprivileged users, for example when a root file system
+# is mounted in a regular user's home directory.
+#
+# https://github.com/systemd/systemd/pull/11820
+#
+
+set -e
+
+rm -fr /tmp/root /tmp/user
+mkdir -p /tmp/root /tmp/user/root
+chown daemon:daemon /tmp/user
+
+# Verify the command works as expected with no prefix or a root-owned prefix.
+echo 'd /tmp/root/test1' | systemd-tmpfiles --create -
+test -d /tmp/root/test1
+echo 'd /test2' | systemd-tmpfiles --root=/tmp/root --create -
+test -d /tmp/root/test2
+
+# Verify the command fails to write to a root-owned subdirectory under an
+# unprivileged user's directory when it's not part of the prefix, as expected
+# by the unsafe_transition function.
+! echo 'd /tmp/user/root/test' | systemd-tmpfiles --create -
+! test -e /tmp/user/root/test
+! echo 'd /user/root/test' | systemd-tmpfiles --root=/tmp --create -
+! test -e /tmp/user/root/test
+
+# Verify the above works when all user-owned directories are in the prefix.
+echo 'd /test' | systemd-tmpfiles --root=/tmp/user/root --create -
+test -d /tmp/user/root/test