7.20 (L1) Virtual machines must deactivate virtual disk shrinking operations

Information

Disabling virtual disk shrinking on virtual machines prevents potential disk unavailability issues. This operation is usually restricted for non-administrative users within the guest environment. The parameter governing this behavior is isolation.tools.diskShrink.disable with a recommended setting of TRUE or Undefined.

Shrinking a virtual disk reclaims unused space in it. If there is empty space in the disk, this process reduces the amount of space the virtual disk occupies on the host drive. Normal users and processes -- that is, users and processes without root or administrator privileges -- within virtual machines have the capability to invoke this procedure. However, if this is done repeatedly, the virtual disk can become unavailable while this shrinking is being performed, effectively causing a denial of service. In most datacenter environments, disk shrinking is not done, so you should disable this feature. Repeated disk shrinking can make a virtual disk unavailable. This capability is available to nonadministrative users in the guest.

Solution

To set this configuration utilize the vSphere interface as follows:

- Select the VM then select Actions followed by Edit Settings
- Click on the VM Options tab then expand Advanced
- Click on EDIT CONFIGURATION
- Click on ADD CONFIGURATION PARAMS then input isolation.tools.diskShrink.disable with a value of TRUE
- Click OK then OK again.

To implement the recommended configuration state, run the following PowerCLI command:

# Add the setting to all VMs
Get-VM | New-AdvancedSetting -Name "isolation.tools.diskShrink.disable" -value $true

Impact:

There is no functional impact noted.

See Also

https://workbench.cisecurity.org/benchmarks/15784

Item Details

Category: CONFIGURATION MANAGEMENT, SYSTEM AND SERVICES ACQUISITION

References: 800-53|CM-1, 800-53|CM-2, 800-53|CM-6, 800-53|CM-7, 800-53|CM-7(1), 800-53|CM-9, 800-53|SA-3, 800-53|SA-8, 800-53|SA-10, CSCv7|5.1

Plugin: VMware

Control ID: b3235eed70c63b688ca46c7c34939249e24c5e5f81600a0d5bbed6e32ecfc526