On Tue, Oct 19, 2021 at 02:44:26PM -0400, Stephen Frost wrote: > Another threat model to consider is if the attacker has read-only access > to the data directory through, say, unix group read privileges or maybe > the ability to monitor the traffic on the SAN, or the ability to > read-only mount the LUN on to another system. This might be obtained by > attacking a backup process where the system was configured to run > physical backups using an unprivileged OS user who only has group read > access to the cluster (and the necessary but non-superuser privleges in > the database system to start/stop the backup), or various potential > attacks at the storage layer. This is similar to the "data at rest" > case above in that XTS works well to address this, but because the > attacker would have ongoing access (rather than just one-time, such as > in the first case), information such as which blocks are being changed > inside of a given 8k page might be able to be determined and that could > be useful information, though a point here: they would already be able > to see clearly which 8k pages are being changed and which aren't, and > there's not really any way for us to prevent that reasonably. As such, > I'd argue that using XTS is reasonable and we can mitigate some of this > concern by using the LSN in the tweak instead of just the block number > as the 'plain64' option in dmcrypt does. That doing so would mean that
That is an excellent point, and something we should mention in our documentation --- the fact that a change of 8k granularity will be visible, and in certain specified cases, 16-byte change granularity will also be visible. -- Bruce Momjian <br...@momjian.us> https://momjian.us EDB https://enterprisedb.com If only the physical world exists, free will is an illusion.
