Comment by viraptor
3 years ago
I'd say this MR is a bad approach in general. The headers say what interfaces are known, not what features are available. You should be able to compile with landlock support on a system which doesn't enable it. Same situation as seccomp and others. Your build machine doesn't have to match the capabilities of the target runner.
But yeah, to test it, you can have a mock version of landlock which responds with the error/success as you want, regardless of what the system would normally do. It relies on the test not being sabotaged too though...
Read the code of the check again. It mostly checks that the required SYS_* constants are defined to be able to use the syscalls. You can compile this on a system that does not have landlock enabled in the running kernel, but the libc (which imports the kernel system call interface) has to provide the syscall numbers.
You're right. I didn't see SYS... symbols being actually used, but they are: https://git.tukaani.org/?p=xz.git;a=blob;f=src/xz/sandbox.c;...
This doesn't change my opinion in general - that version should be exposed through a library call and knowing about the specific syscalls shouldn't be needed in xv.
I see your point, but suggesting adding an additional library dependency while we're discussing a supply chain attack is quite ironic.
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