It's probably not a permissions problem, but a missing DirectoryIndex statement in your /etc/httpd/conf/httpd.conf file. Make sure you have it external to any <Directory> directives so that it becomes a "global" parameter for all directories, not just for the particular directory.
# DirectoryIndex: sets the file that Apache will serve if a directory
# is requested.
# The index.html.var file (a type-map) is used to deliver content-
# negotiated documents. The MultiViews Option can be used for the
# same purpose, but it is much slower.
DirectoryIndex index.html index.html.var
Hope this works.