On 6/11/14, 10:26 AM, Robert Haas wrote:
Now, as soon as we introduce the concept that selecting from a table might not really mean "read from the table" but "read from the table after applying this owner-specified qual", we're opening up a whole new set of attack surfaces. Every pg_dump is an opportunity to hack somebody else's account, or at least audit their activity.


I'm in full agreement we should clearly communicate the issues around pg_dump in particular, because they can't necessarily be eliminated altogether without some major work that's going to take a while to finish. And if the work-around is some sort of GUC for killing RLS altogether, that's ugly but not unacceptable to me as a short-term fix.

One of the difficult design requests in my inbox right now asks how pg_dump might be changed both to reduce its overlap with superuser permissions and to allow auditing of its activity. Those requests aren't going away; their incoming frequency is actually rising quite fast right now. They're both things people expect from serious SQL oriented commercial database products, and I'd like to see PostgreSQL continue to displace those as we reach feature parity in those areas.

Any way you implement finer grained user permissions and auditing features will be considered a new attack vector when you use those features. The way the proposed RLS feature inserts an arbitrary function for reads has a similar new attack vector when you use that feature.

I'm kind of surprised to see this turn into a hot button all of the sudden though, because my thought on all that so far has been a giant so what? This is what PostgreSQL does.

You wanna write your own C code and then link the thing right into the server, so that bugs can expose data and crash the whole server? Not only can you shoot yourself in the foot that way, we supply a sample gun and bullets in contrib. How about writing arbitrary code in any one of a dozen server-side languages of wildly varying quality, then hooking that code so it runs as a trigger function whenever you change a row? PostgreSQL is *on it*; we love letting people write some random thing, and then running that random thing against your data as a side-effect of doing an operation. And if you like that...just wait until you learn about this half-assed rules feature we have too!

And when the database breaks because the functions people inserted were garbage, that's their fault, not a cause for a CVE. And when someone blindly installs adminpack because it sounded like a pgAdmin requirement, lets a monitoring system run as root so it can watch pg_stat_activity, and then discovers that pair of reasonable decisions suddenly means any fool with monitoring access can call pg_file_unlink...that's their fault too. These are powerful tools with serious implications, and they're expected to be used by equally serious users.

We as a development community do need to put a major amount of work into refactoring all of these security mechanisms. There should be less of these embarrassing incidents where bad software design really forced the insecure thing to happen, which I'd argue is the case for that pg_stat_activity example. And luckily so far development resources are appearing for organizations I know of working in that direction recently, as fast as the requirements are rising. I think there's a good outcome at the end of that road.

But let's not act like RLS is a scary bogeyman because it introduces a new way to hack the server or get surprising side-effects. That's expected and possibly unavoidable behavior in a feature like this, and there are much worse instances of arbitrary function risk throughout the core code already.

--
Greg Smith greg.sm...@crunchydatasolutions.com
Chief PostgreSQL Evangelist - http://crunchydatasolutions.com/


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