When you mount the ext4 file system, it uses the permissions that are embedded in that file system. If you wish to override these, then use the following:
1. Find the UID of the user you want to mount as:
id <username> and look for UID=<userid>(<username>) GID=<groupid>(<groupname>)
sudo mount -o nosuid,uid=<userid>,gid=<groupid> /dev/whatever /media/wherever
This will mount the filesystem and mark the specified user as the owner of all files, and the specified group as the group for all files.
nosuid is a security measure that prevents the user from bringing in suid programs and using them to gain root access to the system (i.e, a suid version of bash on the filesystem). Adding the
noexec option will provide additional security, but will prevent the user from executing files on the filesystem.
Note: If you're just trying to interact with the file system yourself, you should either fix the permissions on the device, or interact with it as root if it's just a temporary thing (i.e., recovering a broken install).
If this is for mounting a USB or other removable external drive, you should check out the
pmount system which can automate the process for you, or at least make it considerably easier (i.e.,
pmount <device> should create the folders for you, mount it as your user, and allow you to unmount it as your user)