This article gives various methods to access Linux filesystems
One thing about the virtual machine approach mentionned in this
article is that you could boot the old Linux OS along side OSX,
if that is of any interest.
I guess you want to first copy the files on the disk to a safe place, e.g. your Linux machines HDD or so. Then format the disk with the Mac in Disk Utility in a format which the Linux machine can read and write (ExFAT, I bet). Copy the files back onto it, then connect with the Mac again.