Race condition in rpmioMkpath ("Unable to open temp file: File exists")

[champtar]

Describe the bug
When running multiple rpmbuild in parallel with a non existing %{_tmppath},
if you are lucky enough you will get an error Unable to open temp file: File exists

To Reproduce
Race condition are always a pain to reproduce
-> Code review

Expected behavior
multiple rpmioMkpath in // do not fail

Output

Unable to open temp file: File exists

Environment

• OS / Distribution: EL9.5
• Version: rpm-4.16.1.3-34.el9.x86_64

Additional context

rpm/build/build.cc

Lines 200 to 202 in cae8ef5

	fd = rpmMkTempFile(spec->rootDir, &scriptName);
	if (Ferror(fd)) {
	rpmlog(RPMLOG_ERR, _("Unable to open temp file: %s\n"), Fstrerror(fd));

rpm/rpmio/rpmfileutil.cc

Lines 75 to 108 in cae8ef5

	FD_t rpmMkTempFile(const char * prefix, char **fn)
	{
	const char *tpmacro = "%{_tmppath}"; /* always set from rpmrc */
	char *tempfn;
	static int _initialized = 0;
	FD_t tfd = NULL;
	if (!prefix) prefix = "";
	/* Create the temp directory if it doesn't already exist. */
	if (!_initialized) {
	_initialized = 1;
	tempfn = rpmGenPath(prefix, tpmacro, NULL);
	if (rpmioMkpath(tempfn, 0755, (uid_t) -1, (gid_t) -1))
	goto exit;
	free(tempfn);
	}
	tempfn = rpmGetPath(prefix, tpmacro, "/rpm-tmp.XXXXXX", NULL);
	tfd = rpmMkTemp(tempfn);
	if (tfd == NULL || Ferror(tfd)) {
	rpmlog(RPMLOG_ERR, _("error creating temporary file %s: %m\n"), tempfn);
	goto exit;
	}
	exit:
	if (tfd != NULL && fn)
	*fn = tempfn;
	else
	free(tempfn);
	return tfd;
	}

I don't get error creating temporary file error, only Unable to open temp file: File exists error, so the error is from rpmioMkpath when trying to create %{_tmppath}

rpm/rpmio/rpmfileutil.cc

Lines 125 to 131 in cae8ef5

	rc = stat(d, &st);
	if (rc) {
	if (errno != ENOENT)
	goto exit;
	rc = mkdir(d, mode);
	if (rc)
	goto exit;

If another process create the folder between stat and mkdir we get the error