Merge PR #23469 into master

* refs/pull/23469/head:
	mds: access last std::vector element with `back()`
	mds: disallow certain file operations to "." and ".." dirents

Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>
Reviewed-by: Zheng Yan <zyan@redhat.com>

diff --cc src/include/filepath.h
Simple merge

diff --cc src/mds/Server.cc
Simple merge