Thanks to various airline problems, we had an open spot on the BSDCan schedule. Bob Beck filled in at the last moment with a talk on the first thirty days of LibreSSL. Here are some rough notes on Bob’s talk (slides now available).
LibreSSL forked from OpenSSL 1.0.1g.
Why did “we” let OpenSSL happen? Nobody looked. Or nobody admitted that they looked. We all did it. The code was too horrible to look at. This isn’t just an OpenSSL thing, or just an open source thing. It’s not unique in software development, it’s just the high profile one of the moment.
Heartbleed was not the final straw that caused the LibreSSL fork. The OpenSSL malloc replacement layer was the final straw. Default OpenSSL never frees memory, so tools can’t spot bugs. It uses LIFO recycling, so you can use after free. The debugging malloc sends all memory information to a log. Lots more in Bob’s slides, but this all combined into an exploit mitigation technique countermeasure. Valgrind, Coverity, and OpenBSD’s randomized memory tools don’t catch this.
Someone discovered all this this four years ago and opened an OpenSSL bug. It’s still sitting there.
LibreSSL started by ripping out features. VMS support, 16-bit Windows support, all gone.
As an example, how does OpenSSH (not LibreSSL, but another OpenBSD product) do portable?
- No ifdef maze
- No compromise on what the intrinsic functions actually do
- Standard intrinsics
- Don’t reimplement libc
How does OpenSSL do portable?
The result? “Chthulhu sits in his house in #define OPENSSL_VMS and dreams”
Removed scads of debugging malloc and other nasties.
What upstream packages call and use them? No way to tell. LibreSSL makes some of the very dangerous options no-ops. Turn on memory debugging? Replace malloc wrappers at runtime? These do nothing. The library internally does not use them.
Some necessary changes that were implemented in massive sweeps:
OpenSSL used EGD for entropy, and faked random data. OpenSSL gathered entropy from the following sources:
In LibreSSL, entropy is the responsibility of the OS. If your OS cannot provide you with entropy, LibreSSL will not fake it.
LibreSSL is being reformatted into KNF – the OpenBSD code style. OpenSSL uses whatever style seemed right at the moment. The reformatting makes other problems visible, which is the point. More readable code hopefully means more developer involvement.
The OpenSSL bug tracking RT has been and continues to be a valuable resource.
OpenSSL exposes just about everything via public header files. Lots of the API should probably not be used outside of the library, but who knows who calls what? OpenBSD is finding out through constant integration testing with their ports tree.
The LibreSSL team wants to put the API on a diet so that they can remove potentially dangerous stuff. Their guys are being careful in this by testing against the OpenBSD ports tree. Yes, this conflicts with the “drop-in replacement” goal.
Internally, LibreSSL uses only regular intrinsic functions provided by libc. OpenSSL’s custom APIs remain for now only to maintain compatibility with external apps.
Surprises LibreSSL guys in OpenSSL:
LibreSSL has added the following cipher suites under acceptable licenses – Brainpool, ChaCha, poly1305, ANSSI FRP256v1, and several new ciphers based on the above.
FIPS mode is gone. It is very intrusive. In other places governments mandate use of certain ciphers (Cameilla, GOST, etc). As long as they’re not on by default, and are provided as clean implementations under an acceptable license they will include them. They believe it’s better people who must use these use them in a sane library with a sane API than rolling their own.
If you want to use the forthcoming portable LibreSSL, you need:
You can’t replace explicit_bzero with bzero, or arc4random with random. LibreSSL wants a portability team that understands how to make it work correctly.
LibreSSL’s eventual goals:
There’s lots of challenges to this. The biggest is stable funding.
The OpenBSD Foundation wants to fund several developers to rewrite key pieces of code. They want to sponsor efforts of the portability team, and the ports people track the impact of proposed API changes.
They will not do this at the expense of OpenSSH or OpenBSD.
The OpenBSD Foundation has asked the Linux Foundation for support, but the Linux Foundation has not yet committed to supporting the effort. (I previously said that they hadn’t responded to the request, which is different. The LF has received Bob’s email and discussions are ongoing.)
If you’re interested in supporting the effort, contact the OpenBSD Foundation. The Foundation is run by Bob Beck and Ken Westerback, and they manage all funding. (While Theo de Raadt leads the OpenBSD Project, he actually has nothing to do with allocating funding.)