Infrastructure Software

I looking for validation and clarification of the usage of permission on devices presented by OS (Oracle Linux 5 update 2) and those by ASM (11.2.0.2). I thought I'd start here before the ASM group.

* Hard Disks existing on local server and external storage device
* UDEV presents disks to OS user as device files located at /dev
***** SCSI devices follow specific naming convention sda, sdb etc.
***** UDEV assigns ROOT as owner and 640 permissions by default for device files
* UDEV can be used to change permission and ownership of device files without changing the unlining device file owner and permission through the use of a UDEV configuration file
* ASMLib Device Driver Configuration establishes
***** Creates the /etc/sysconfig/oracleasm configuration file
***** Creates the /dev/oracleasm mount point
***** Mounts the ASMLIB driver file system
**********ASMLib driver file system points to /dev/oracleasm mount point
* Marked and Scanned ASM Disk are represented in the ASMLib driver file system as device files
***** The permission on the device files inside ASMLib file system have permissions set to the those used to configure the driver using /etc/init.d/oracleasm configure (ie. user=GRID group=OINSTALL)
***** The asm device files have permissions=660.

The HD device files have an owner=ROOT, group=DISK and permission=640. The ASM file system has device files have user=GRID, group=OINSTALL and permissions=660. The Oracle user has primary group=OINSTALL.
How is RDBMS owner (Oracle user) able to write to the HD device when owner, group and permissions don't seem to provide access?
What means does the Oracle, Grid, Root or combination use to get permission to write to HD devices.

Thanks in advance.