Re: [Bug-tar] Security Question - Unused File Space from a file'sEOF to end of physical block on disk

[Joerg Schilling]

"Stone, Todd -Systems" <address@hidden> wrote:

> Our system contains both UNCLASSIFIED and CLASSIFIED data.  Our security 
> agency (AF-CERT in our case) have procedures for copying from a mixed 
> classification system to UNCLASSIFIED media.
>
> Files occupy full blocks and the concern is over contents of the unused 
> (slack) space between the files's EOF (End-of-File) marker and physical end 
> of the data block as occupied on disk.  This unused data could be considered 
> CLASSIFIED if contents aren't zeroed out.  Does or has anyone modified 
> GNU-TAR to clear unallocated (slack) space?
>

You cannot reliably and (you should not) do this inside a tar implementation.

If the OS you are using does not do this by default, you should chose another
OS or filesystem implemenataion. I cannot speak for other OS, but Solaris 
grants you to clear the space at leat on UFS and I would guess this is also 
true for ZFS.

Jörg

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