stable inclusion
from stable-5.10.10
commit fdcaa4af5e70e2d984c9620a09e9dade067f2620
bugzilla: 47610

--------------------------------

commit 51b2ee7d upstream.

If you export a subdirectory of a filesystem, a READDIRPLUS on the root
of that export will return the filehandle of the parent with the ".."
entry.

The filehandle is optional, so let's just not return the filehandle for
".." if we're at the root of an export.

Note that once the client learns one filehandle outside of the export,
they can trivially access the rest of the export using further lookups.

However, it is also not very difficult to guess filehandles outside of
the export.  So exporting a subdirectory of a filesystem should
considered equivalent to providing access to the entire filesystem.  To
avoid confusion, we recommend only exporting entire filesystems.
Reported-by: NYoujipeng <wangzhibei1999@gmail.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>