[Crash/Fuzzing] RangeError in ssz library when parsing empty BeaconBlock

[pventuzelo]

Describe the bug

During fuzzing with beaconfuzz, I found this RangeError crash inside the ssz library when providing an empty beaconblock.

Expected behavior

Should detect and throw an Error.

Steps to Reproduce

crash_RangeError_block_lodestar.js:

var mainnet_1 = require("@chainsafe/lodestar-types/lib/ssz/presets/mainnet");

buf = Buffer.from('', 'hex')

mainnet_1.types.BeaconBlock.deserialize(buf);

Run:

$ npm i @chainsafe/lodestar-types

$ node crash_RangeError_block_lodestar.js
/home/scop/node_modules/@chainsafe/ssz/lib/backings/structural/container.js:99
        offsets.push(start + fixedSection.getUint32(index, true));
                                          ^

RangeError: Offset is outside the bounds of the DataView
    at DataView.getUint32 (<anonymous>)
    at /home/scop/node_modules/@chainsafe/ssz/lib/backings/structural/container.js:99:43
    at Array.reduce (<anonymous>)
    at ContainerStructuralHandler.fromBytes (/home/scop/node_modules/@chainsafe/ssz/lib/backings/structural/container.js:97:33)
    at ContainerStructuralHandler.deserialize (/home/scop/node_modules/@chainsafe/ssz/lib/backings/structural/abstract.js:55:17)
    at ContainerType.deserialize (/home/scop/node_modules/@chainsafe/ssz/lib/types/composite/abstract.js:112:28)
    at Object.<anonymous> (XXX/crash_RangeError_block_lodestar.js:6:29)
    at Module._compile (internal/modules/cjs/loader.js:936:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:947:10)
    at Module.load (internal/modules/cjs/loader.js:790:32)

Desktop (please complete the following information):

• OS: Ubuntu 18.04
• @chainsafe/lodestar-types: 0.8.0
• nodejs: v12.9.1