Did you use the same username when you installed fuduntu as you have in ubuntu? If it was not different it is possible that fuduntu may have changed permissions of all the files in /home.
However it may be worth starting ubuntu in recovery mode, assuming you can, then mounting the ubuntu partitions as read/write instead of read only with
though as it is the /home partition, not root that is at fault, you may not even need that command.
mount -o rw,remount /
You can then try changing ownership of the /home partition back to your ubuntu username with
and also permissions to the ubuntu default with
chown -R username:username /home/username
It is also worth looking for the UID of the fuduntu user to see if that is different from the ubuntu UID of 1000 for the first user, though I am not sure if or how you can change that back; perhaps the chown and chmod commands will do it for you.
chmod -R 755 /home.#/username
This is, indeed a salutary lesson not to try and share the same user in a /home partition; use the same partition by all means, but make sure you have a different username and therefore home folder within /home for each OS