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Xz: Can you spot the single character that disabled Linux landlock?

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Re: Xz: Can you spot the single character that disabled Linux landlock?

#141

Post by saagarjha »

asvitkine wrote: post #129
hermitdev wrote: post #105

Earlier quoted context omitted.

That's kind of the point. It's feature detection code. If the code cleanly compiles, the feature is assumed supported, otherwise, it's assumed not present/functional. This pretty common with autotools. The gotcha here is this innocuous period is not supposed to be syntactically valid. It's meant to be subtle and always disable the feature.

Shouldn't whatever is depending on xz supporting landlock be verifying that it's the case through blackbox tests or something? Otherwise a check like this even without the bug could end up disabling landlock if e.g. the compiler environment was such that a given header wasn't available...

Yes, this is intentionally how autoconf is supposed to work.

Re: Xz: Can you spot the single character that disabled Linux landlock?

#142

Post by astrange »

Aurornis wrote: post #5
jstanley wrote: post #4

Earlier quoted context omitted.

What does the dot do?

The function is “check_c_source_compiles”. The comment indicates that the intention is to confirm that the Landlock functionality can be compiled on the system, in which case it will be enabled. The stray dot isn’t valid C, so it will never compile. By ensuring it can never compile, Landlock will never be enabled.

configure would print that it's not enabled, so it seems like the kind of thing people would eventually notice.

Re: Xz: Can you spot the single character that disabled Linux landlock?

#143

Post by usr1106 »

thrtythreeforty wrote: post #6
jstanley wrote: post #4

Earlier quoted context omitted.

What does the dot do?

Fails the build, so that Landlock support is never enabled.

I don't think it fails the build. It's part of a test, trying to compile a bit of code. If it compiles the test is true and a certain feature is enabled. If the compilation fails the the feature is disabled.

This is quite common in build systems. I had such a test produce incorrect results in the kernel build system recently. The problem is that the tests should really look carefully for an expected error message. If the compilation fails with the expected message the test result is false. If the compilation fails for some other reason the build should fail so the developer is forced to investigate.

Disclaimer: I have not studied the xz build system in detail, just what I saw from the diff plus a bit of extrapolation.

Re: Xz: Can you spot the single character that disabled Linux landlock?

#144

Post by deckard1 »

Dalewyn wrote: post #127
kristopolous wrote: post #110

Earlier quoted context omitted.

Ok there's a larger question here about the bazaar software development method. How can we ensure say, that Microsoft doesn't pay someone to throw a wrench in libre office development or Adobe to sabotage Gimp? There's lots of deception strategies for bad faith actors and given the paucity of people who actually do the work, it's really really hard to be picky. Especially with the complexity of library dependencies.…

>How can we ensure say, that Microsoft doesn't pay someone to throw a wrench in libre office development or Adobe to sabotage Gimp? Microsoft and Adobe have reputations to uphold long into the future. Is that infallible? Hell no it isn't, but consider that Jia Tan only needed to uphold his reputation insofar as getting his backdoor onto everyone's systems. Once that is done, his reputation or the lack thereof becomes…

You say all this after recent documents were revealed about Facebook intercepting and analyzing Snapchat encrypted traffic via a man-in-the-middle conspiracy.

Re: Xz: Can you spot the single character that disabled Linux landlock?

#145

Post by db48x »

Denvercoder9 wrote: post #82
kllrnohj wrote: post #73

Earlier quoted context omitted.

Hey, leave C++ out of this. This is a C problem. https://en.cppreference.com/w/cpp/feature_test

That only works for language features though, it doesn't allow detecting OS/library features.

Very true, but don’t forget that Autoconf checks for “interesting” compiler choices as well as library and OS features. And then there is libtool, which abstracts out the differences between how compilers generate shared libraries so that you only have to understand one way of doing it and it will work on all of them.

Re: Xz: Can you spot the single character that disabled Linux landlock?

#146

Post by bawolff »

kristopolous wrote: post #132
Dalewyn wrote: post #127

Earlier quoted context omitted.

>How can we ensure say, that Microsoft doesn't pay someone to throw a wrench in libre office development or Adobe to sabotage Gimp? Microsoft and Adobe have reputations to uphold long into the future. Is that infallible? Hell no it isn't, but consider that Jia Tan only needed to uphold his reputation insofar as getting his backdoor onto everyone's systems. Once that is done, his reputation or the lack thereof becomes…

Those companies are famous for skullduggery. They can secure the dominance of their offering against the open source competition for well under 500k a year. It's a no brainer. What this might look like would be say, poorly discernable icons, clumsy UI design, or an unstable API that makes plugins constantly break. Large volumes of documentation that are inadequate or inaccurate in critical places, etc. If I was malic…

> Those companies are famous for skullduggery

There are levels of skull duggery. Hiring someone to pretend to work for a competitor while secretly sabotaging them is a whole other level of skullduggery with a lot of liability attached. I don't think that would be worth it to them.

Re: Xz: Can you spot the single character that disabled Linux landlock?

#147

Post by esafak »

deckard1 wrote: post #144
Dalewyn wrote: post #127

Earlier quoted context omitted.

>How can we ensure say, that Microsoft doesn't pay someone to throw a wrench in libre office development or Adobe to sabotage Gimp? Microsoft and Adobe have reputations to uphold long into the future. Is that infallible? Hell no it isn't, but consider that Jia Tan only needed to uphold his reputation insofar as getting his backdoor onto everyone's systems. Once that is done, his reputation or the lack thereof becomes…

You say all this after recent documents were revealed about Facebook intercepting and analyzing Snapchat encrypted traffic via a man-in-the-middle conspiracy.

What kind of a reputation do you think Facebook has?

Re: Xz: Can you spot the single character that disabled Linux landlock?

#148

Post by usr1106 »

Where/how was landlock supposed to be used?

I guess you cannot really use it in a generic library like compression/decompression. The library has no clue what the program is supposed to do and what should be restricted.

For a program it might be clearer.

The sshd attack was using liblzma as a library. So disabling landlock seems unrelated? A sign that there is more bad code waiting to be detected / had been planned to be inserted???

Re: Xz: Can you spot the single character that disabled Linux landlock?

#149

Post by bawolff »

CGamesPlay wrote: post #93

On an unrelated note, this malware team has assembled a great dataset for training AIs on identifying security problems. Every commit has some security problem, and the open source community will be going through and identifying them. (Thanks, maintainers, for the cleanup work; definitely not fun!)

I doubt it will generalize well. At best its just an arms race.

Re: Xz: Can you spot the single character that disabled Linux landlock?

#150

Post by db48x »

acdha wrote: post #84
db48x wrote: post #57

Earlier quoted context omitted.

Yea, it’s not impossible to do, just not standardized. If you use a library and it provides useful version information, then definitely use it. It’s just that the language or the tooling doesn’t force libraries to have that kind of metadata. Compare that with Rust, where every library you use must come with a standardized manifest that includes a version number, and where they tell library authors up front that they…

> It used to be the case that any program targeting Unix had to either spend a lot of time and energy tracking the precise differences between dozens of different commercial Unices, or use autoconf. Autoconf was the project that combined all of that lore into a single place, so that most people didn’t have to know every single detail. As a data point, the place I worked for in the mid-90s had a single codebase with s…

Ah, wacky fun. https://youtu.be/yHPvOeahQnc?t=87
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