Failure to start if /tmp is mounted noexec

[perkinslr]

This issue occurs when only Valkyrien Skies and addons are installed and no other mods

• I have tested this issue and it occurs when no other mods are installed

Minecraft Version

1.19

Mod Loader

Forge

Issue description

During early startup, VS unpacks the linux-native libKrunchJni64.so into /tmp and then tries to load it. The loading step fails if /tmp/ is mounted noexec. Security-minded installations often mount /tmp/ noexec because /tmp/ is generally an inappropriate place to store executable code, even briefly.

There are several alternative locations where the file could be stored. The most obvious would be in ${game_directory}/libraries/org/valkyrienskies/, ideally with a version number attached. ${game_directory}/libraries already must exist, and must have execute permissions or minecraft wouldn't be starting in the first place.

The second obvious option is ${natives_directory}, which likewise should exist and be executable. In practice, the default MC launcher creates this directory and populates it, for some versions, on the fly and removes it after the game exits. It is often possible to start the game without this existing, but if the goal is to have the native actually be transient, it's a solid choice.

After that, it's down to platform specific locations. It could go in ${XDG_RUNTIME_DIR} if the goal is to have it transient, but that might not be set on servers. It generally falls back to /tmp, which isn't ideal. Many programs stick this sort of thing inside ${XDG_STATE_HOME}, falling back to ${HOME}/.local/share if it is unset, so the usual directory would end up being ${HOME}/.local/share/valkyrienskies or similar. The obvious drawback is it leaves orphaned files outside of MC's usual paths, but at least they are in the correct location outside MC's usual paths. ${XDG_CACHE_HOME} (${HOME}/.cache) is another option, better by-spec than $DATA, but less often used by programs in the wild.

Issue reproduction

Set up MC+VS, server or client, on a Linux box.

Remount /tmp/ noexec

sudo mount -o remount,noexec /tmp

Start MC, observe the failure.

As an alternative, you can use a container (firejail, docker) to start MC, with a private /tmp/ configured noexec and observe the failure

firejail --noprofile --private-tmp --noexec=/tmp bash
# then start MC as usual.

Logs

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