On 12/21/2010 06:12 AM, Kenneth Buckler wrote:
Hello,
I am investigating security requirements for configuring a PostgreSQL
database on a Linux system.
One of the security requirements our organization would like to
implement is "trusted startup", in that PostgreSQL would verify the
authenticity of the binaries and configuration files before making the
database available to users.
Do you have a trusted boot path from BIOS to bootloader to kernel to
init core userspace, where everything is digitally signed (by you or
someone else) and verified before execution? Do you disable kernel
module loading?
If not, you're wasting your time, because a compromise by malicious
kernel module, modified init, modified md5 command, etc will render your
precautions totally pointless.
If your BIOS can't verify the bootloader, which is likely on an x86 /
x64 system, then you can still get some protection by signing your
kernels and using a bootloader that checks signatures. If someone messes
with the bootloader you lose, but it'll help protect you against obvious
automated attacks. You might be able to use the Trusted Platform Module
(TPM) on your machine to get a fully verified chain of trust, though, by
using Trusted GRUB.
http://trousers.sourceforge.net/grub.html
If you can reasonably trust that the kernel you loaded is OK, you can
have it verify signatures on binaries before executing them. There was a
DigSig project for that (http://disec.sourceforge.net/) but it seems to
have stopped recently. I'm not sure if there's any replacement.
Without kernel-level signature verification, all you can really do is
have a custom initrd/initramfs (signed and verified by grub during boot)
that checks the signatures on init, md5, gpg, libc, etc etc (any binary
root runs, including scripts) before switching to the real root FS
during boot. Then you can have your Pg startup scripts (which you signed
on a separate, trusted machine) verify GnuPG signatures of the Pg
binaries before execution.
All in all, it's a painful, clumsy way to do things, and AFAIK there's
little support in mainline Linux systems for trusted boot and
trusted-binary systems. You might find out more with a search for "linux
trusted computing", "linux trusted boot", "linux tpm", "linux signed
binaries", etc.
Personally, I'd be using existing system- and network-level intrusion
detection tools like tripwire and snort to try to spot intrusion if and
when it happens. I'm not confident that a chain-of-trust approach is
workable on Linux systems at present, though I'd love to be proved wrong
by being pointed at existing support I've missed.
--
Craig Ringer
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