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Comment by girvel | Hacker News Reader

This is an interesting thought. Currently, it is unsafe and intended to load only the files you trust. I should definitely include a warning into README.

Overall, it would be nice to make it safer. I don't think switching to non-Lua format would make it safer, because it is intended to serialize functions too, which can have arbitrary code even if everything else would be stored as data. Maybe it is possible to make a function like `ldump.safe_load` restricting `load`'s environment, so it wouldn't have access to debug/os/io modules.

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You could take a look at SELÖVE, a (severely out of date) fork of LÖVE that is intended to make it safe to run arbitrary .love games. (It used to be on bitbucket, but it looks like it's gone? I'm not sure if I have the repo locally :/)

Running arbitrary code was such a problem that I just completely ruled it out for bitser. Instead of serializing functions, you can register safe functions as resources. This doesn't solve the upvalue problem, though.

I looked into it, and Lua allows limiting the environment when `load`ing -- through `env` argument since 5.2 or through setfenv before. I will add a helper function to produce a minimal needed environment for safe loading and a documentation page about safety.

Note that loading (maliciously crafted) bytecode is generally not safe in Lua; sandboxing can be escaped in more ways than what's possible when loading plaintext sourcecode, and there are no full mitigations for this currently as far as I know (and would probably be highly interpreter/version sensitive anyway)-- the only "real" mitigation strategy is to just not `load` bytecode at all.

But this is probably a non-issue for a lot of usecases.

See e.g.

https://gist.github.com/corsix/6575486

https://www.corsix.org/content/malicious-luajit-bytecode

This is fascinating. I wonder if this issue exists in Lua5.2+, where there is no jit and `load` is able to restrict used environment.

Yes, exists. Here is an example for 5.2:

https://ia903205.us.archive.org/15/items/ARMArchitectureRefe...

Yeah, you would need an allowlist for functions. Using bytecode would make it much harder, I haven't given deep thought yet.

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