Disallow mounting folders on the guest's root for WASIX modules

[Arshia001]

No description provided.

[promptless]

📝 Documentation updates detected! A separate PR for documentation updates has been made here: wasmerio/docs.wasmer.io#122

[charmitro]

Maybe a helper function for this? It is used in fs v2 and v3. Something like (not tested),

fn check_volume_path(
    mount_path: &PathBuf,
    package: &str,
) -> Result<(), Error> {
    if mount_path.as_path() == Path::new("/") {
        bail!(
            "The \"{package}\" package wants to mount a volume at \"/\", but that's not allowed",
        );
    }
    Ok(())
}

[Arshia001]

if only the code was that clean to begin with... it has been my experience that attempting to make clean implementations in code that's not clean by design usually leads to more complexity down the line, so when I see duplicate code, I also duplicate mine, to at least keep the code consistently unclean.

[charmitro]

I'd love a const about "/", const ROOT_PATH: &str = "/"; or similar. What do you think?

[Arshia001]

I'd happily approve of someone else doing that XD / is well-known enough to warrant not giving it a const of its own though.

[charmitro]

Also,

Tested-by: Charalampos Mitrodimas [email protected]

[syrusakbary]

This PR might have some implications, that we don't want. I remember other programs using mapdir=.:/ to make Python work for example. We may want to use that directory instead (and not mount any other dir) if / is provided. Lets follow up in a sync

[Arshia001]

@syrusakbary in fact, that's exactly what this PR is trying to prevent. Mounting things on / messes up a lot of assumptions in WASIX, including:

• We put commands from packages in /bin and /usr/bin. If / is mounted, those will get overwritten and be inaccessible.
• Packages mount volumes, which contain necessary files without which they won't run. Python is in fact a great example of this. If I were to just mount something on /, I'd lose all the data files that came with the python package, ending up with a broken application.
  • Same with PHP, if I mount a website's root on /, I lose all the openssl data files and HTTPS will be broken for example.
  • I do believe python was the motivation behind the custom behavior of mounting . on /home with --dir .. I think that's what you're thinking of as well.