Moving luac from position results in server crash

[Bastrabun]

Repro:

1. Place a luacontroller
2. Add this code:

interrupt(0.1,'')

3. Use Worldedit to remove the luacontroller

Another Repro:

1. Place luacontroller
2. Place a digilines piston next to it
3. Place a second luacontroller that would be moved by the extending piston
4. Add this code to the first luacontroller

digiline_send('',"extend")
interrupt(0.1,'')

This is what happens:

2021-06-02 07:39:09: ERROR[Main]: ServerError: AsyncErr: environment_Step: Runtime error from mod 'mesecons_luacontroller' in callback environment_Step(): .../.minetest/mods/mesecons/mesecons_luacontroller/init.lua:472: bad argument #1 to 'pairs' (table expected, got nil)
2021-06-02 07:39:09: ERROR[Main]: stack traceback:
2021-06-02 07:39:09: ERROR[Main]: 	[C]: in function 'pairs'
2021-06-02 07:39:09: ERROR[Main]: 	.../.minetest/mods/mesecons/mesecons_luacontroller/init.lua:472: in function 'create_environment'
2021-06-02 07:39:09: ERROR[Main]: 	.../.minetest/mods/mesecons/mesecons_luacontroller/init.lua:627: in function 'run_inner'
2021-06-02 07:39:09: ERROR[Main]: 	.../.minetest/mods/mesecons/mesecons_luacontroller/init.lua:686: in function 'run'
2021-06-02 07:39:09: ERROR[Main]: 	.../.minetest/mods/mesecons/mesecons_luacontroller/init.lua:753: in function 'action'
2021-06-02 07:39:09: ERROR[Main]: 	/home/mtlive1/.minetest/mods/digilines/internal.lua:106: in function 'transmit'
2021-06-02 07:39:09: ERROR[Main]: 	/home/mtlive1/.minetest/mods/digilines/init.lua:53: in function 'receptor_send'
2021-06-02 07:39:09: ERROR[Main]: 	.../.minetest/mods/mesecons/mesecons_luacontroller/init.lua:724: in function <.../.minetest/mods/mesecons/mesecons_luacontroller/init.lua:718>
2021-06-02 07:39:09: ERROR[Main]: 	...mtlive1/.minetest/mods/mesecons/mesecons/actionqueue.lua:137: in function 'old_execute'
2021-06-02 07:39:09: ERROR[Main]: 	/home/mtlive1/.minetest/mods/mesecons_debug/overrides.lua:7: in function 'execute'
2021-06-02 07:39:09: ERROR[Main]: 	...mtlive1/.minetest/mods/mesecons/mesecons/actionqueue.lua:111: in function <...mtlive1/.minetest/mods/mesecons/mesecons/actionqueue.lua:73>
2021-06-02 07:39:09: ERROR[Main]: 	...ve1/5.4.1/Minetest_live/bin/../builtin/game/register.lua:422: in function <...ve1/5.4.1/Minetest_live/bin/../builtin/game/register.lua:406>
2021-06-02 07:39:09: ERROR[Main]: stack traceback:

This is how it can be fixed:

 local function run(pos, event)

+       if string.sub(core.get_node(pos).name,0,36) ~= "mesecons_luacontroller:luacontroller" then
+               return false, "Luac does not exist anymore"
+       end
        local meta = minetest.get_meta(pos)
        local code = meta:get_string("code")
        local ok, errmsg = run_inner(pos, code, event)

Thanks to Test_User who discovered it and whosit who debugged it and found a solution.

For my reference: #610

[numberZero]

Doesn’t sound like our bug but as defensive coding, the workaround can be accepted. I’d also check for the controller ID, to not run the code on a wrong controller should there be one.

[fluxionary]

it seems that the crash here has been mitigated by a nil check since the bug was reported:

code, as it was when this was reported:

mesecons/mesecons_luacontroller/init.lua

Lines 470 to 472 in d356f90

	local vports = minetest.registered_nodes[minetest.get_node(pos).name].virtual_portstates
	local vports_copy = {}
	for k, v in pairs(vports) do vports_copy[k] = v end

code, as it is now:

mesecons/mesecons_luacontroller/init.lua

Lines 477 to 484 in 54de66b

	local node_def = minetest.registered_nodes[minetest.get_node(pos).name]
	if not node_def then return end
	local vports = node_def.virtual_portstates
	if not vports then return end
	local vports_copy = {}
	for k, v in pairs(vports) do vports_copy[k] = v end

however i haven't tested whether there's still a crash if a luac is WE'ed or MVPS'ed, there might be other problems.

[numberZero]

it seems that the crash here has been mitigated by a nil check since the bug was reported:

@fluxionary thanks for noticing! Tested with Mesecons piston and Digistuff piston. No crash or other problems.