core: Don't try to apply non-root uid/gid when run as non-root

In an unprivileged case, we can't do this on the real filesystem. For
`ex container`, we want to completely ignore uid/gid.  I added a test
installing `httpd` which failed previously.

TODO: For non-root `--ex-unified-core` we need to do it as a commit modifier.

Closes: #940
Approved by: jlebon

src/libpriv/rpmostree-core.c

@@ -2682,6 +2682,14 @@ apply_rpmfi_overrides (RpmOstreeContext *self,
                        GCancellable  *cancellable,
                        GError       **error)
 {
+  /* In an unprivileged case, we can't do this on the real filesystem. For `ex
+   * container`, we want to completely ignore uid/gid.
+   *
+   * TODO: For non-root `--ex-unified-core` we need to do it as a commit modifier.
+   */
+  if (getuid () != 0)
+    return TRUE;  /* 🔚 Early return */
+
   int i;
   g_auto(rpmfi) fi = NULL;
   gboolean emitted_nonusr_warning = FALSE;

tests/ex-container-tests/test-httpd.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/bash
+set -xeuo pipefail
+
+cd ${test_tmpdir}
+
+dn=$(cd $(dirname $0) && pwd)
+. ${dn}/../common/libtest-core.sh
+
+cat >httpd.conf <<EOF
+[tree]
+ref=httpd
+packages=httpd;
+repos=fedora;
+EOF
+
+# This one has non-root ownership in some of the dependencies, but we shouldn't
+# try to apply them; see apply_rpmfi_overrides().
+rpm-ostree ex container assemble httpd.conf
+ostree --repo=repo ls httpd /usr/sbin/httpd