VirtualBox comes with a feature to give you access to the hosts’s filesystem through a CIFS server. This is available after you’ve installed the Guest Additions drivers in the Guest. More details are available here (specific to Ubuntu but can apply to all versions of Linux): https://help.ubuntu.com/community/VirtualBox
There are more details at that page on how to set up the share.
Frustratingly, the CIFS (Shared Folder) server name you access a hosts file system on a Linux Guest is different to one that you use under Windows so as a quick overview
Windows Guest
net use x: vboxsvrshare
Linux Guest
mount -t vboxsf share mountpoint
Note the change from vboxsvr under Windows to vboxsf under Linux.
