ksmbd: check invalid FileOffset and BeyondFinalZero in FSCTL_ZERO_DATA

commit b5e5f9df

 upstream.

FileOffset should not be greater than BeyondFinalZero in FSCTL_ZERO_DATA.
And don't call ksmbd_vfs_zero_data() if length is zero.

Cc: stable@vger.kernel.org
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>