How to change user permissions on the /blocks/ folder in linux?
You should be able to change the permissions of the block files using the following command:

sudo chmod -R go+r .bitcoin/


(replacing .bitcoin/ with your Bitcoin data directory)

The problem is that bitcoind will create all new files with permissions so that only allow the owner of the files can read from and write to them (600), because of the following line in init.cpp:

umask(077);


I have created a patch and a pull request that should fix this, though: https://github.com/bitcoin/bitcoin/pull/4286