Security Fix in Open BSD

#1

Post by wglb » Thu, Dec 16, 2010, 10:12 PM UTC

Security Fix in Open BSD
code.bsd64.org

Re: Security Fix in Open BSD

#2

Post by tedunangst » Thu, Dec 16, 2010, 10:37 PM UTC

Fix is 8 years old.

Re: Security Fix in Open BSD

#3

Post by gcr » Thu, Dec 16, 2010, 10:46 PM UTC

Is this related to the alleged IPSEC backdoor? Either way, could we get some context?

Re: Security Fix in Open BSD

#4

Post by Thangorodrim » Thu, Dec 16, 2010, 10:49 PM UTC

Looking only at that diff, the fix is a break.

It inverts the sense of the test so that the authenticator of the packet is used even if the tag is null.

Re: Security Fix in Open BSD

#5

Post by ctcherry » Thu, Dec 16, 2010, 10:50 PM UTC

Could someone explain the significance of this change? What would this enable or disable in practice?

Re: Security Fix in Open BSD

#6

Post by david_p » Thu, Dec 16, 2010, 10:50 PM UTC

tedunangst wrote: post #2

Fix is 8 years old.

I believe this is a follow-up to this story : http://marc.info/?l=openbsd-tech&m=129236621626462&w...

I think the purpose of the link is to demonstrate some "suspicious" changes in the IPSEC code.

Re: Security Fix in Open BSD

#7

Post by tptacek » Thu, Dec 16, 2010, 10:51 PM UTC

In 2001, Angelos Keromytis --- then a grad student at Penn, now a Columbia professor --- added support for hardware-accelerated IPSEC NICs. When you have an IPSEC NIC, the channel between the NIC and the IPSEC stack keeps state to tell the stack not to bother doing the things the NIC already did, among them validating the IPSEC ESP authenticator. Angelos' code had a bug; it appears to have done the software check only when the hardware had already done it, and skipped it otherwise.

The bug happened during a change that simultaneously refactored and added a feature to OpenBSD's ESP code; a comparison that should have been == was instead !=; the "if" statement with the bug was originally and correctly !=, but should have been flipped based on how the code was refactored.

HD Moore may as we speak be going through the pain of reconstituting a nearly decade-old version of OpenBSD to verify the bug, but stipulate that it was there, and here's what you get: IPSEC ESP packet authentication was disabled if you didn't have hardware IPSEC. There is probably an elaborate man-in-the-middle scenario in which this could get you traffic inspection, but it's nowhere nearly as straightforward as leaking key bits.

To entertain the conspiracy theory, you're still suggesting that the FBI not only introduced this bug, but also developed the technology required to MITM ESP sessions, bouncing them through some secret FBI-developed middlebox.

One year later, Jason Wright from NETSEC (the company at the heart of the [I think silly] allegations about OpenBSD IPSEC backdoors) fixed the bug.

It's interesting that the bug was fixed without an advisory (oh to be a fly on the wall on ICB that day; Theo had a, um, a, "way" with his dev team). On the other hand, we don't know what releases of OpenBSD actually had the bug right now.

It seems vanishingly unlikely that there could have been anything deliberate about this series of changes. You are unlikely to find anyone who will impugn Angelos. Meanwhile, the diffs tell exactly the opposite of the story that Greg Perry told.

Re: Security Fix in Open BSD

#8

Post by tptacek » Thu, Dec 16, 2010, 11:05 PM UTC

Thangorodrim wrote: post #4

Looking only at that diff, the fix is a break. It inverts the sense of the test so that the authenticator of the packet is used even if the tag is null.

The "tag" is an mbuf tag. Mbuf tags aren't packet data; think of them like per-packet session state, so that different layers of the stack (the network drivers, any driver required to handle crypto goo done on the card, the original IP code, and the IPSEC decapsulation and handling code) can talk to each other without hand-coding a million disgusting callbacks throughout the kernel.

In this code, "mtag" is the tag matching PACKET_TAG_IPSEC_IN_CRYPTO_DONE, which the lower-level drivers use to tell the IPSEC code that the NIC already did verification. If the tag isn't there, then you want to do the verification in software, which is what the fixed code does and the broken code didn't do.

Re: Security Fix in Open BSD

#9

Post by paperclip » Thu, Dec 16, 2010, 11:21 PM UTC

I presume you are attempting to imply that this one of the 'leet' FBI backdoors that the Perry email discussed. It would help if you actually said why you thought this patch was interesting when submitting it to HN.

I hope we are not going to get a rash of inarticulate HN submissions for every minor patch to openbsd which may have security implications.

I doubt this is in anyway related to the recent drama.

The initial bad patch which broke things looks like v1.63 of the file. This was committed in 2001 by angelos.

Note: - angelos has a greek email address (for what it is worth) - 1.63 was committed in 2001; the allegations of backdoors seem to be from 2000 and 1999 - it appears to break things for all non-ipsec aware nics. This seems to broad an error for an intentional backdoor

It also looks like the code didn't make it to a release branch before being fixed - so if it was an attempted backdoor, it was not successful.

Disclaimer: I have no experience with BSD kernel code nor with IPSEC.

Edit: I initially thought that angelos also commited the fix as well. I think I need to get my eyes tested

Re: Security Fix in Open BSD

#10

Post by calloc » Thu, Dec 16, 2010, 11:29 PM UTC

ctcherry wrote: post #5

Could someone explain the significance of this change? What would this enable or disable in practice?

As Thomas Ptacek more accurately describes in his post, this disables the ESP Auth checks (after the fix) if the NIC has already completed them. Before the fix, the software ESP auth check would run only when the NIC had already done them, so never if the NIC had not done them.