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Re: postgres zeroization of dead tuples ? i.e scrubbing dead tuples with sensitive data. - Mailing list pgsql-general

From Melvin Davidson
Subject Re: postgres zeroization of dead tuples ? i.e scrubbing dead tuples with sensitive data.
Date
Msg-id CANu8FiyhqhXGn0UO0brMsJG-ZBw4h2gP0kjXCVw-MrjfTZSkiQ@mail.gmail.com
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In response to Re: postgres zeroization of dead tuples ? i.e scrubbing dead tuples with sensitive data.  (Alvaro Herrera <alvherre@2ndquadrant.com>)
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Which begs the question, what is more important, the old/vacuumed data, or the current valid data?
If someone can hack into the freed data, then they certainly have the ability to hack into the current valid data.
So ultimately, the best thing to do is to secure the system from being hacked, not zero out old data.
AFAIK, the only time you need to zero out the bytes is when you are decommissioning the disk, in which case ALL data on the disk needs to be wiped.

On Wed, Nov 18, 2015 at 3:13 PM, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
David G. Johnston wrote:
> On Wed, Nov 18, 2015 at 12:45 PM, Day, David <dday@redcom.com> wrote:

> > I believe the   concern,  based on my current understanding  of postgres
> > inner workings,  is  that when a dead tuple is reclaimed by vacuuming:  Is
> > that reclaimed space initialized in some fashion that would  shred any
> > sensitive data that was formerly there to any  inspection by  the
> > subsequent owner of  that disk page ? ( zeroization )

No.  Ultimately, space occupied by dead tuples is "freed" in
PageRepairFragmentation(), src/backend/storage/page/bufpage.c;
the contents of the tuples are shuffled to "defragment" the free space,
but the free space is not zeroed.  You could certainly try to read the
unused page and extract some data from there.

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Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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Melvin Davidson
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