Dirperm1 is a mount option, that comes with systems that have recent aufs version.
There is a brief mention of Dirperm1 in this docs:
https://docs.docker.com/reference/builder/#known-issues-run
However, the link to man page seems broken right now.
If your docker info says Dirperm1 Supported: true, then you don’t have to worry about his issue at all. If it says Dirperm1 Supported: false and if you are facing a file permissions problems that can occur when using the AUFS file system, then you would require to see the workaround in that issue page.