Ubuntu Windows GIT Samba share file permission on "pull" and "checkout"

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http://serverfault.com – I know there are a lot of similar questions about file permissions on Git and sharing, but none seem to address my particular problem. I've got a Ubuntu virtual machine, there is a Git repo that is shared via Samba so I can edit the files from my Windows dev machine. My problem is when I do git checkout of git pull the file permissions get set so that the Samba guest user can't edit the files. I've tried fixing this with a git hook and a chmod -R 777 but this makes big repos slow, as git thinks every file has changed, even with core.filemode false set. This is the share set up in Samba: (HowTos)