Important update,
based on latest update "Insider Build 17063" there has been significant change in permissions. In very short, you need to:

sudo umount /mnt/c
sudo mount -t drvfs C: /mnt/c -o metadata

Relevant links:
https://github.com/Microsoft/WSL/issues/3181
https://blogs.msdn.microsoft.com/commandline/2018/01/12/chmod-chown-wsl-improvements/
https://blogs.windows.com/windowsexperience/2017/12/19/announcing-windows-10-insider-preview-build-17063-pc/#cbUAtBrErr1A3JJA.97